History

CHAPTER VI

Schistosomiasis

Malcolm S. Ferguson, Ph. D., and Frederik B. Bang, M.D.

The first human schistosome was discovered by Bilharz in Cairo, Egypt, in 1851. Later it was found that Schistosoma haematobium was the cause of hematuria, then a common condition in the fellaheen population. Schistosomiasis, however, is an ancient disease; eggs of S. haematobium have been found in mummies dating back to 1250 B.C. During the Middle Ages, hematuria was described by Arabian physicians, but it is not certain that they referred to the type endemic in Egypt. That an endemic disease was related to hematuria in the Nile Valley was first mentioned in 1808. In 1847, the oriental type of schistosomiasis was recognized by Fujii as being endemic in Japan; this was a half century before the discovery of Schistosoma japonicum by Fujinami and Katsurada. The third human blood fluke, Schistosoma mansoni, was finally differentiated from S. haematobium in 1915, but it is of interest to note that Bilharz had described its lateral-spined eggs more than 70 years earlier.

Although schistosomiasis resulting from infestation with S. haematobium is an ancient disease and presumably has affected soldiers for centuries in times of both war and peace, it was not until the 18th century that the disease manifested its military importance. During Napoleon's Egyptian campaigns between 1799 and 1801, his troops suffered severely from hematuria. A century later, British and Australian troops acquired schistosomiasis during the Boer War. The British list more than 300 cases from this campaign; during the period from 1901 to 1911, more than 600 infections were diagnosed in troops who had served in endemic areas of South Africa. An outbreak of schistosomiasis occurred in Egypt among British garrison troops in 1912. During World War I, only a few dozen British troops acquired the disease in Egypt and Mesopotamia, but service in the Middle East during this period accounted for 157 recognized cases among Australian soldiers. After the war, in 1921, 31 men of a British garrison became infected while they were camped along the Euphrates River in Mesopotamia. Only five cases of schistosomiasis were listed as having been acquired by Italian troops during the Ethiopian campaign in 1935.

The Germans were aware of the problem of schistosomiasis in north Africa. From 1940 to 1942, while their troops were in that area, they studied methods of preventing the infection. A few cases of the disease occurred

among German prisoners of war who had become infected in the Sweet Water Canal. The most extensive experience of the British with the disease during World War II was in the West African Force in which 432 British and 1,279 African troops developed clinical symptoms after exposure in a lagoon in southern Nigeria immediately before they were transported to India.

Elsewhere, during World War II, British troops acquired a few infections. There were 42 cases among soldiers in the Middle East and 2 cases in the British North African Force. In Africa and the Middle East, Australian troops contracted very few infections. During the liberation of the Philippines in 1944, however, 144 men developed schistosomiasis japonica.

Experience of U.S. military personnel with schistosome infections before World War II was negligible, having been confined to a few cases among naval personnel from ships stationed in Chinese inland waters and among Puerto Rican members of U.S. Armed Forces. Early in World War II, the Preventive Medicine Service of the Surgeon General's Office and civilian scientists recognized that U.S. troops would probably be called upon to operate in areas where human schistosomes were endemic. Publications disseminated information concerning the three schistosome infections (their distribution, etiology, epidemiology, diagnosis, treatment, and prevention) and speculated on the likelihood that some U.S. troops would become infected, either during battle operations or while off duty. As late as July 1944, in spite of warnings by the Preventive Medicine Service,¹ certain line officers considered schistosomiasis to be a disease of nonmilitary importance in the Philippines and one likely to affect only a small number of troops. The first operation for the liberation of the Philippines (later in 1944) resulted in the exposure on Leyte of thousands of U.S. troops to the infective stage of S. japonicum. All three species of human blood flukes were encountered during the period from 1941 to 1945, but, fortunately, only oriental schistosomiasis proved to be of military importance.

Geographic distribution of human schistosomes.-According to the estimates of Stoll, there may be as many as 114 million human schistosome infections throughout the world.² S. japonicum occurs in vast areas of China, in five small foci in Japan, in several islands of the Philippines, in Formosa, and in one known region of the Celebes (map 1). The strain which occurs in Formosa apparently is not well adapted to man. S. haematobium and S. mansoni overlap somewhat in distribution, but infestation with the latter is much more widespread. S. mansoni occurs in Africa, principally in a band across the central region of the continent; in Madagascar; in South America, in Brazil, Surinam, and Venezuela; and in some of the islands of the West Indies, especially Puerto Rico (map 2). S. haematobium occurs more extensively in Africa than does S. mansoni. S. haematobium is present

¹War Department Technical Bulletin (TB MED) 68, 18 July 1944.
²Stoll, N. R.: This Wormy World. J. Parasitol. 33 : 1-18, February 1947.

MAP 1.-Geographic distribution of Schistosoma japonicum.

throughout the continent of Africa and in Madagascar, as well as in southern Portugal and in Israel, Iran, Iraq, Syria, Saudi Arabia, and Yemen.

Life cycle of human schistosomes.-The adults of S. haematobium, S. mansoni, and S. japonicum all live in the blood vessels and there deposit large number of eggs which reach the outside of the body either in urine

MAP 2.-Geographic distribution of Schistosoma haematobium and Schistosoma mansoni.

or feces. S. haematobium inhabits principally the vesical and pelvic venous plexuses, and eggs deposited in the blood vessels of the bladder escape into the lumen and are eliminated in the urine. If worms are present in the rectal venules, eggs may also be found in the feces. Both S. mansoni and S. japonicum live usually in the mesenteric veins, and eggs deposited in large numbers in the veins of the wall of the small and large intestine leave the body in the feces.

The life cycles of the three human schistosomes are similar and are not complicated trematode life histories, since only two hosts are required-man, or certain other mammals, and a few species of fresh-water snails (fig. 3). However, maintenance of the cycles depends largely on the sanitary practices of man with regard to the disposal of his body wastes. For survival and development of the parasite, urine or feces containing eggs must reach fresh water shortly after leaving the body. There, the larvae (miracidia) hatch almost immediately from the eggs and invade the appropriate species of snail if it happens to be present. Within the snail host, the miracidium develops into a mother sporocyst which gives rise to large numbers of daughter sporocysts, each of which may produce thousands of fork-tailed larvae called cercariae. These cercariae escape from the snail and can swim actively in water. One infected snail may release large numbers of cercariae over

FIGURE 3.-The epidemiology of schistosomiasis and the infection of military

many weeks. Capable of living in water for a day or two, the cercariae are infective for man and can penetrate the skin on contact. The cercariae lose their tails during penetration, invade the blood vessels, follow a migration route in the body, and eventually reach the veins (mesenteric, vesical, or pelvic) in which they grow into either male or female blood flukes ranging in length from 10 to 25 mm., depending on the sex and species. The females of S. mansoni and S. japonicum lay their eggs in the venules of either the small or large intestine; S. haematobium deposits its eggs in the bladder.

ACTIVITIES IN ZONE OF INTERIOR

The Army was concerned with human schistosomes both within the Zone of Interior and in oversea areas. During the period 1942 to 1945, inclusive, there were recorded approximately 2,500 cases of schistosomiasis (table 8). Activities in the United States consisted of conducting certain laboratory studies, of publishing and disseminating information concerning, schistosomiasis, and of taking precautions against the introduction of schistosomiasis into this country by returning servicemen who were infected.

Outside the continental limits of the United States, the Army was concerned primarily with the prevention of schistosome infection in troops operating in endemic areas. Field and laboratory investigations of the schistosomiasis problems were also carried on in endemic areas.

TABLE 8.-Incidence of schistosomiasis in the U.S. Army, by theater or area and year, 1942-45

Area	1942-45		1942		1943		1944		1945
Area	Number of cases	Rate	Number of cases	Rate	Number of cases	Rate	Number of cases	Rate	Number of cases	Rate
Continental United States	194	0.01	---	0	8	0	11	0	175	0.06
Overseas:
North America¹	---	---	---	---	---	---	---	---	---	---
Latin America	633	1.66	29	.28	79	.65	235	2.74	290	3.98
Europe	5	.00	---	---	---	---	---	---	5	.00
Mediterranean²	22	.01	---	---	1	.00	16	.02	5	.01
Middle East	---	---	---	---	---	---	---	---	---	---
China-Burma-India	19	.04	---	---	1	.03	13	.08	5	.02
Pacific Ocean Area	116	.09	1	.01	1	.00	4	.01	110	.29
Southwest Pacific	1,545	.84	1	.01	---	---	84	.16	1,460	1.41
Total overseas³	2,350	.22	31	.05	82	.05	352	.09	1,885	.41
Total Army	2,544	.10	31	.01	90	.01	363	.05	2,060	.27

¹Includes Alaska and Iceland.
²Includes North Africa.
³Includes 10 admissions on transports in 1945.

Educational Measures

The Preventive Medicine Service of the Office of the Surgeon General prepared a number of publications on the prevention and control of schistosomiasis for use by military personnel both in the United States and overseas. On 9 June 1941, The Surgeon General issued Circular Letter No. 56, in which the etiology, distribution, treatment, and prevention of schistosomiasis resulting from infestation with S. mansoni were discussed. This letter was intended for use in the Caribbean Defense Command. As yet, the United States was not at war with Germany or Japan. In February 1943, another circular letter dealing with all three types of schistosomiasis appeared. This material had been compiled after consultation with the Subcommittee on Tropical Diseases, Division of Medical Sciences, National Research Council, and with experts of the Navy and of the National Institute of Health, U.S. Public Health Service. Subsequently, during the period April 1944 to April 1946, inclusive, medical and sanitary data concerning Formosa, the Philippine Islands, Japan, southeastern China, and northeastern China, in all of which schistosomiasis occurred, were published in TB MED's (War

Department Technical Bulletins) 30, 68, 160, 171, and 220, respectively. It should be noted that in these publications schistosomiasis japonica was considered to be of potential military importance in China and Japan, whereas, in the Philippines, the disease was considered a serious one but of nonmilitary importance and likely to affect only small numbers of troops. Eventual experience in the Philippines showed that the dangers to troops had not been correctly appraised. Whether schistosomiasis japonica would have been a serious military problem in China or Japan is a matter of speculation.

After the appearance of hundreds of cases of schistosomiasis japonica in troops on Leyte, Philippine Islands, early in 1945, TB MED 167, a rather comprehensive discussion of this disease, was published in June 1945. This publication placed particular emphasis on the life history of the parasite and on the diagnosis, treatment, and prevention of the disease.

Early in 1945, the Preventive Medicine Service arranged that two motion pictures on schistosomiasis japonica be made in the United States, primarily from footage acquired in the Philippines. One production, a short training film on S. japonicum, was to be used for the indoctrination of troops scheduled to invade Japan. This film was not completed until October 1945, more than a month after the end of the war in the Pacific. The second production, a professional technical version in color for the instruction of personnel of the Medical Department, was begun in April 1945 but was not released until after the end of the war.

Sanitary Precautions

About the middle of 1945, the policy of the Army was to concentrate at two tropical disease centers, Harmon General Hospital, Longview, Tex., and Moore General Hospital, Swannanoa, N.C., soldiers who had been returned to the United States after being treated for schistosomiasis japonica overseas. At first, both the Army and the U.S. Public Health Service were concerned³ about the possibility that raw sewage from these hospitals flowing into streams might create a hazard if viable schistosome eggs were being discharged and suitable snail hosts of S. japonicum were present in these waters. No precautions were taken at Harmon General Hospital because the sewage flowed into brackish water, but at Moore General Hospital the raw sewage was chlorinated for a few weeks.⁴

In August 1945, the chlorination procedure was discontinued by the Corps of Engineers because it was believed chlorination could not be relied upon to kill viable eggs or miracidia and because no suitable snail host for S. japonicum had been shown to exist in the particular areas in question. History would appear to support this action, since no species of schistosome

³Letter, Thomas Parran, Surgeon General, U.S. Public Health Service, to Gen. Norman T. Kirk, The Surgeon General, U.S. Army, 11 Aug. 1945.
⁴Memorandum, Col. W. A. Hardenbergh, SnC, Director, Sanitary Engineering Division, Office of the Surgeon General, for Maj. Choice B. Matthews, 18 Aug. 1945, subject : Sewage Treatment at Moore and Harmon General Hospitals.

of man has ever become established in this country in spite of the facts that presumably thousands of people from Africa, China, the Philippines, and Japan who were infected with schistosomes have come to this country and that the conditions under which these people have lived in this country would not meet present-day sanitary standards.

Van Cleave⁵ was apprehensive that returning servicemen might be responsible for the establishment of human blood flukes in the United States. On the other hand, Stoll⁶ did not regard the introduction of schistosomes after World War II as a public health threat. He cites Peltier who, in 1929, noted that no autochthonous case of schistosomiasis had been known to occur in France, although infected soldiers had been entering that country for more than 100 years. Failure of the disease to become established there may be due to the lack of a suitable molluscan host. Brumpt and other French workers have exposed a large number of species of snails to schistosome miracidia without finding any that were susceptible. Returning soldiers were reported to have been responsible for the establishment of a limited, and now extinct, focus of infection in western Australia after the Boer War.⁷ However, because a snail host was never identified and the laboratory diagnosis may have been in error, Fairley suspects that an area of endemicity may never have existed in Australia.⁸ More recently in India, experiments with snails by two groups of investigators failed to demonstrate a species that would become infected with S. haematobium or S. mansoni derived from African troops stationed in that country.⁹

A note of caution should be added here, however, since it was found in 1945 that, under certain laboratory conditions, cercariae of S. mansoni develop in the American snail, Tropicorbis havanensis. Similarly, it was determined that S. japonicum develops in the laboratory in the American snail Pomatiopsis lapidaria.¹⁰ The field significance of these findings has yet to be demonstrated.

⁵(1) Van Cleave, H. J.: Some Influences of Global War Upon Problems of Disease. J. Am. Dietet. A. 21: 513-515, September-October 1945. (2) Van Cleave, H. J.: Returning Service Men, A Problem in National Health. Am. Sci. 32 : 243-253, January 1944.
⁶Stoll, N. R. : Changed Viewpoints on Helminthic Disease ; World War I vs. World War II. Ann. New York Acad. Sc. 44: 207-224, 30 Sept. 1943.
⁷Official History of the Australian Army Medical Services, 1914-18. Vol. 1, Melbourne : H. J. Green, Government Printer, 1930, p. 776. Vol. 3, Sidney : Halstead Press Pty. Ltd., 1943, pp. 266-267.
⁸Letter, N. Hamilton Fairley, Hospital for Tropical Diseases, London, to Dr. M. S. Ferguson, U.S. Public Health Service, 27 May 1952, subject : Bilharzia Disease.
⁹Mukerji, A. K., Bhaduri, N. V., and Narain, S.: Experiments on the Transmission of Human Schistosomiasis in India. Indian J.M. Research 34: 311-315, October 1946.
¹⁰(1) Cram, E. B., Jones, M. F., and Wright, W. H. : A Potential Intermediate Host of Schistosoma mansoni. Science 101: 302, March 1945. (2) Cram, E. B., Files, V. S., and Jones, M. F.: Experimental Molluscan Infection With Schistosoma mansoni and Schistosoma haematobium, Experiments With Schistosoma mansoni. In Nat. Inst. Health Bull. No. 189, January 1947, pp. 81-94. (3) Ward, P. A., Travis, D., and Rue, R. E.: Experimental Molluscan Infection With Schistosoma japonicum: Preliminary Small-Scale Experiments With Native Amnicolids During 1945. In Nat. Inst. Health Bull. No. 189, January 1947, pp. 95-100. (4) Berry, E. G., and Rue, R. E.: Pomatiopsis lapidaria (Say), an American Intermediate Host for Schistosoma japonicum. J. Parasitol. 34 (Supp.) : 15, December 1948.

Investigations

Numerous projects pertaining to schistosome problems were initiated in this country by the Preventive Medicine Service, particularly in the period 1943-45. During the war, these studies were classified, and observations resulting from them were circulated only among civilian schistosomiasis investigators, Army, Navy, and U.S. Public Health Service personnel, and other responsible individuals. The bulk of the research work was carried on by personnel at universities under contracts with the Office of Scientific Research and Development; the Naval Medical Research Institute; and the National Institute of Health, U.S. Public Health Service, which conducted extensive investigational programs. The Preventive Medicine Service had proposed many of these projects, and certain studies on schistosomes were conducted in Army medical laboratories. Contributions from Army installations resulted mainly from investigations on the preparation and testing of antigenic materials and on the detection of schistosome ova in feces. The latter research yielded several techniques of definite value in diagnosing schistosome infections.

Studies at centers other than those of the Army were concerned with-

1. A search for possible snail hosts of human schistosomes in the United States.
2. Research on the development of the schistosomes in experimental mammalian hosts.
3. The cercaricidal effects of water-treatment processes.
4. The effects of sewage treatment on schistosome ova.
5. The protective value of untreated and chemically treated cloth fabrics.
6. Repellent ointments to protect the skin from cercariae.
7. Intradermal and serologic tests to determine infection.
8. The chemotherapy of schistosomiasis.

In these investigations, the Army contributed information and advice from those members of the Medical Department who had had experience with schistosomiasis. It also supplied materials for the experiments and a continuous supply of live snails collected in the Far East.

Investigations with S. mansoni, particularly at the National Institute of Health, began in May 1943, when an infected monkey was imported from Puerto Rico. Two months earlier, eggs of the molluscan host in Puerto Rico had been received and used in establishing colonies of Australorbis glabratus in the United States. Tests of the susceptibility of American snails to infection with S. haematobium became possible when a baboon that had been infected in Egypt was received at New York University on 7 July 1944. The infected baboon had been brought to this country from Egypt by Dr. Claude H. Barlow, who had exposed himself a few weeks before to cercariae of S. haematobium. Dr. Barlow proposed to go about the United States with a trailer and use the ova being excreted in his urine to determine whether any native species of snails would become infected with this parasite in its natural habitat. It was thought that a human infection would give more

conclusive results than an infection in lower animals because man apparently is the only natural host in endemic areas and also because of the possibility that passage through laboratory animals might produce biological changes which would alter the susceptibility of snails to infection. It did not prove feasible for Barlow to use his infection for field studies in the United States.

As early as 3 April 1944, the U.S. Public Health Service requested that the Medical Department of the Army attempt to import into the United States from China live specimens of the molluscan host of S. japonicum.¹¹ Considerable effort was put into the project, but no Chinese snails were received in this country. It was not until 23 January 1945, some months after the invasion of Leyte, that dogs and live specimens of the snail host Oncomelania quadrasi, infected with S. japonicum, were received from the Philippines. Subsequently, when infected snails were collected by Army personnel and forwarded regularly from Leyte to the National Institute of Health, it was possible to initiate experimental work with the cercariae and adults of the oriental schistosome.

It should be mentioned at this point that the Preventive Medicine Service of the Office of the Surgeon General decided early in 1945 that it would be desirable for a group of specialists on schistosomes to go to the Philippines to undertake the study of a number of militarily pertinent problems concerning schistosomiasis japonica.¹² This project was approved by the theater commander, and in April 1945 a Subcommission on Schistosomiasis of the Commission on Tropical Diseases, Army Epidemiological Board, arrived on Leyte.

EXPERIENCE IN OVERSEA THEATERS

The bulk of the U.S. Army's experience with schistosomiasis and with the causative agents of the disease was in the Orient during 1944 and 1945. Before this, however, infection with both S. haematobium and S. mansoni had been encountered to a limited extent in U.S. troops in other theaters. As nearly as can be determined, no investigational work on S. haematobium was conducted by the Army during the war. On the other hand, several important studies on methods of diagnosing infections due to S. mansoni were initiated in Puerto Rico.

Schistosoma haematobium

During the North African campaign (Operation TORCH), which was begun in November 1942, U.S. troops came into the only region in which they encountered S. haematobium. Although troops were stationed in countries of Asia Minor where the parasite occurs, there were no known cases of infection. It may be significant to note here that Asia Minor was not a

¹¹Letter, R. E. Dyer, Director, National Institute of Health, to Brig. Gen. S. Bayne-Jones, Office of the Surgeon General, 31 Mar. 1944.
¹²Annual Report, Commission on Tropical Diseases, Army Epidemiological Board, 19 Apr. 1945?19 Apr. 1946.

combat area for U.S. soldiers. Since the disease occurs all across northern Africa from Morocco to Egypt, in both coastal areas and oases, it is surprising that so few cases of infection occurred during the fighting in Tunisia. The low incidence of infection with this parasite cannot be attributed to a special educational program regarding schistosomiasis or to supervisory efforts of medical personnel. Need for avoiding contact with untreated fresh water in endemic areas was stressed in an article in the Medical Bulletin of the North African Theater of Operations, May 1944, but schistosomiasis was not considered to be an important communicable disease.

Only about 22 cases of infection with S. haematobium were recorded for the U.S. Army in the Mediterranean theater; exposure data are available for 17 of these. During July 1943, 14 men from a U.S. Army Air Corps service squadron bathed in a fresh-water pool close to Gafsa, Tunisia. Subsequently, after repeated urine examinations, three of these soldiers were proved to be infected with S. haematobium. The infections were apparently light, since the men were asymptomatic.¹³ Also in July 1943, another group of U.S. Army Air Corps personnel swam in a fresh-water pond 5 miles east of Gafsa, Tunisia. These men had become separated from a convoy traveling from Oran, Algeria, and spent several days crossing the desert. With no medical officer to warn them, and understandably in the mood for contact with water, 35 of the 60 men went swimming. Of these 35 soldiers, 12 were later proved to have acquired schistosomiasis. The majority of the men developed clinical symptoms of the disease, only two being asymptomatic.¹⁴ The only other available records of the disease refer to two soldiers who developed hematuria after exposure to cercariae in the fall of 1943, one while bathing in a watering trough near Mateur, Tunisia, and the other while swimming in a river flowing through Mateur.¹⁵

No schistosome infections were acquired in the China-Burma-India theater. The small number of cases reported for this area were in men who had become infected with S. haematobium in north Africa or with S. mansoni in Puerto Rico.¹⁶

Schistosoma mansoni

Infection in troops.-The known distribution of S. mansoni is in areas of the world where the troops of the United States were not required to fight. It does not occur to any extent in north Africa and, therefore, was not encountered during Operation TORCH. Regulations were issued concerning contact with fresh water in Puerto Rico, but there was a disregard for them, and maneuvers were even held in endemic areas. However, only one U.S.

¹³Letter, Surgeon, North African Theater of Operations, to Surgeon, 557th Service Squadron, 43d Service Group, 7 Aug. 1944, subject : Cases of Schistosoma haematobium.
¹⁴Letter, Surgeon, U.S. Forces, India-Burma Theater of Operations, 11 Jan. 1945, subject : Reported Case of Schistosomiasis (enclosure I).
¹⁵Essential Technical Medical Data, Headquarters, North African Theater of Operations. U.S. Army, for April 1944.
¹⁶Blumgart, H. L., and Pike, G. M. : A History of Internal Medicine in the India-Burma Theater of Operations, 1945, p. 140. [Official record.]

soldier is recorded as having acquired the disease. This man became infected in Puerto Rico in 1943, about 2 months after reaching the island. No information is available regarding his method of exposure. On the other hand, medical officers of the Army did encounter a considerable number of cases of infestation with S. mansoni in Puerto Rican soldiers who were infected before being inducted into the service. Cases of the disease in Puerto Ricans within the United States and in oversea areas were also discovered during the war; for example, 55 men in an antiaircraft gun battalion stationed in California in 1945 were found to be infected. Medical records indicate that about 850 infections due to S. mansoni were diagnosed.

Before April 1943, Puerto Ricans were taken into the Army without any screening for schistosome infection. After that date, however, a man otherwise physically and mentally fit was rejected if he was found, on the basis of one stool specimen, to be passing eggs of S. mansoni. This screening led to the rejection of from 9 to 14 percent of the Selective Service registrants each month.¹⁷ There is evidence from autopsy records, skin tests, and repeated stool examinations that approximately 40 percent of the men in one group of Puerto Rican soldiers on duty in the Canal Zone were infected with S. mansoni.¹⁸ It should be pointed out that many of the troops in the Canal Zone had been inducted before the screening process for schistosome infections was inaugurated. Even so, it was estimated that about 10 percent of the infected men were missed by the screening process. This was possible because most of those eventually found to be infected were asymptomatic. The large number of infected troops led to a consideration of the possibility that schistosomiasis might be endemic in the Canal Zone and in the Republic of Panama, since an infantry regiment of Puerto Ricans had been stationed at Empire, Canal Zone, during and following World War I. No screening of these troops for schistosome infection had been done, and the men had bathed in natural fresh water in both the Canal Zone and the Republic of Panama. In 1943, with the arrival in the Canal Zone of known infected Puerto Rican soldiers, the question of the health hazard of S. mansoni was raised. Since there was no indication that the parasite had been introduced by Puerto Ricans during or after World War I, since Australorbis glabratus, the molluscan host of S. mansoni in the New World, has not been found in the Canal Zone, and since studies at the School of Tropical Medicine, San Juan, P.R., failed to show that any of several species of snails collected in the Canal Zone would become infected with S. mansoni, it was concluded that there was at that time no danger of the introduction of the disease.

Puerto Rican soldiers infected with S. mansoni were stationed in other areas of the Antilles Department, including Saint Lucia and Trinidad, Brit-

¹⁷Annual Report, Surgeon, Antilles Department, 1944.
¹⁸(1) Professional History of Preventive Medicine in World War II, 1 January 1940 to 1 October 1945, The Panama Canal Department, vol. I., pp. 120-121. [Official record.] (2) Weller, T. H., and Dammin, G. J.: The Incidence and Distribution of Schistosoma mansoni and Other Helminths in Puerto Rico. Puerto Rico J. Pub. Health & Trop. Med. 21 : 125-147, December 1945.

ish West Indies, and Curacao, Netherlands West Indies. The disease is endemic in Saint Lucia, but the only cases encountered in military personnel were in native-born Puerto Ricans.¹⁹

Air Corps personnel were stationed in Brazil, where schistosomiasis is widespread, but no cases of the disease in these men were reported. The presence of the disease there and means of avoiding it were stressed in directives.²⁰

Investigations.-Medical personnel in the Caribbean Defense Command (Antilles Department, including Puerto Rico, and Panama Canal Department) conducted a series of investigations on the occurrence and diagnosis of schistosomiasis, both independently and in collaboration with the School of Tropical Medicine, San Juan, P.R.

Personnel at the Antilles Department Medical Laboratory²¹ made a study of the prevalence and distribution of S. mansoni in Puerto Rico. On the basis of only one stool examination, 1,909, or 9.9 percent, of 19,139 Puerto Rican Selective Service registrants were shown to be infected with S. mansoni. These records also pointed up several new foci of the disease on the island. The infection was found to be almost twice as prevalent among craftsmen as among farm laborers.

In August 1944, antigen prepared from cercariae and adults of S. mansoni at the School of Tropical Medicine, San Juan, was used to skin test 1,000 Puerto Rican troops in the Panama Canal Department.²² Following this trial, it was proposed that the skin test be used on a larger scale, and in November all otherwise physically qualified selectees were skin tested at the Induction Station, Fort Buchanan, P.R. The program was purely investigative in character, and a positive reaction was not to be the basis for rejection for military service. The results of these studies were not conclusive because of difficulties with the sterility of the antigen and because many skin-test?negative individuals were found to have stools positive for S. mansoni.

Further research on diagnostic methods conducted by the Army consisted of a study of the acid-ether centrifugation and zinc sulfate flotation techniques as methods for the recovery of eggs of S. mansoni. In spite of inherent disadvantages, the acid-ether technique was found to be superior to the zinc sulfate flotation method.²³ A rectal scraper, another possible aid to the recovery of schistosome ova from infected persons, was developed and tested by the Army Medical Laboratory in San Juan.

¹⁹History of Medical Department Activities, Antilles Department, Preventive Medicine, pp. 61?65. [Official record.]
²⁰Essential Technical Medical Data, U.S. Army Forces, South Atlantic, for January 1944. Enclosure 2 thereto.
²¹See footnote 18(2), p. 56.
²²See footnote 17, p. 56.
²³(1) Weller, T. H., and Dammin, G. J.: The Acid-Ether Centrifugation and the Zinc Sulfate Flotation Techniques as Methods for the Recovery of the Eggs of Schistosoma mansoni. Am. J. Trop. Med. 25: 367-374, July 1945. (2) Weller, T. H., and Dammin, G. J.: An Improved Method of Examination of Feces for the Diagnosis of Intestinal Schistosomiasis. Am. J. Clin. Path. 15 : 496-500, November 1945.

Schistosoma japonicum

The Army's principal contact with blood-fluke disease occurred during the liberation of the Philippines. Troops were exposed to the larvae of S. japonicum on Leyte from October 1944 on into the early months of 1945. The subsequent outbreak of schistosomiasis was the signal for a more rigid enforcement of regulations regarding contact with fresh water and the invoking of other preventive measures, including a more intensive educational program. At the same time, U.S. medical personnel were afforded a unique opportunity to study the clinical aspects of this unfamiliar disease and to determine the value of therapeutic drugs in a large group of men who could be kept under close supervision for an extended period of time. The outbreak also provided additional incentive to those who had been working on laboratory and field aspects of the human schistosome problem in Leyte and led to the eventual development of three separate investigational programs on the island.

In retrospect, it must be recognized that on Leyte certain factors other than the preventive activities conducted by the Army were important in limiting the number of cases of the disease. First, the fighting had moved out of the endemic areas on the island before the first case of schistosomiasis was diagnosed late in December 1944, and, once an area was secured, camp sanitation practices such as the erection of showers using well water, eliminated most of the chance for exposure to water infested with cercariae. Combat activities involving contact with infested water were likewise over, since organized Japanese resistance had ended by late December. When soldiers began to come down with the disease, exhaustive inquiries were made to identify the waters in which they had been exposed. It became apparent that swamps, small streams, even fairly large rivers-in fact, all surface fresh water-should be avoided for swimming and for the washing of clothing and vehicles. The numerous laboratory and field investigations carried out were productive as sources of valuable information, but they contributed little to the actual control of schistosomiasis on Leyte.

In addition to the troops who acquired schistosome infections during the liberation of Leyte, about 30 percent of the U.S. prisoners of war who survived internment at the Davao Penal Colony on Mindanao, Philippine Islands, were infected with S. japonicum. The circumstances responsible for the exposure of these prisoners of war were different from those under which the troops became infected on Leyte and will be discussed separately.

Endemicity in the Philippines

In 1906, the first pathological observations of schistosomiasis japonica in the Philippines were reported, with the prediction that the disease would be found to be endemic in the islands. By 1941, nearly 30 papers reporting on

this disease had appeared, and it was then known that S. japonicum infected people on Leyte, Samar, Mindoro, and Mindanao. Later, it was determined that schistosomiasis is endemic in southeastern Luzon.²⁴

Schistosomiasis japonica among prisoners of war

At the Army Medical Department Professional Service School, Washington, D.C., late in 1945, five of the released U.S. prisoners of war who had been interned for many months at the Davao Penal Colony in southern Mindanao were found by members of the Department of Parasitology to be infected with S. japonicum.²⁵ Because of the high mortality among prisoners of the Japanese, the approximate number of men who contracted schistosomiasis near Davao will never be known.

Exposure to infested water probably occurred in most cases while the prisoners were working in labor details in the Mactan ricefields a short distance from the penal colony. Schistosomiasis was apparently not diagnosed in any of the prisoners before their release in 1945, but many of the prisoners, while interned, suffered from a syndrome called "Dapeco fever," the cause of which was not known. Many of the symptoms associated with this syndrome resemble those of schistosomiasis; for example, fever, eosinophilia, urticaria, and gastrointestinal disturbances. It is of interest to note that some of the Japanese guards also suffered from "Dapeco fever."

Before World War II, the only known endemic area of schistosomiasis japonica on the island of Mindanao was in the northeastern section in the province of Surigao.²⁶ It is of historical interest that the type specimens of Oncomelania quadrasi, the molluscan host of S. japonicum in the Philippines and described by Moellendorf in 1895, were collected in Surigao. Studies carried on by the United States in 1945 showed that the disease is much more widely distributed on the island.²⁷

²⁴Pesigan, T. P.: The Endemicity of Schistosomiasis Japonica in Sorsogon, Southeastern Luzon. J. Philippine M.A. 24: 19-27, January 1948.
²⁵Subsequent investigations conducted by the Army and Navy and, especially, a study sponsored by the Veterans' Administration have revealed that many of these unfortunate men had contracted the infection. In 1953, Dr. Harry Most, of the New York University College of Medicine, reported to the senior author that about 400 of the original 2,000 prisoners at the penal colony had survived internment and that 378 of the 400 had been studied since 1946. On the basis of one or more stool examinations, 116, or about 30 percent, of these men had been found to be passing viable eggs of S. japonicum. Repeated stool examinations and study of rectal biopsy specimens would probably have raised this percentage considerably, inasmuch as 50 percent of a small group of men studied shortly after their release from prison had been found positive.
²⁶Africa, C. M., and Garcia, E. Y. : The Distribution of Schistosomiasis Japonica in the Philippines. Philippine J. Pub. Health 2: 54-62, 1935.
²⁷Studies made by the Philippine Government since 1948 have also indicated that the disease is widely distributed on the island. It is now known to be present in every province except Misamis Oriental (Wright, W. H., McMullen, D. B., Faust, E. C., and Bauman, P. M. : The Epidemiology of Schistosomiasis Japonica in the Philippine Islands and Japan. II. Surveys for Schistosomiasis Japonica on Mindanao, Philippine Islands. Am. J. Hyg. 45: 164-184, March 1947). In addition, field investigators have found the molluscan host of the oriental blood fluke breeding in areas adjacent to the Mactan ricefields in which the prisoners of war had worked (Pesigan, T. P., Pangilinan, M. V., and Sarmiento, A. P. : Studies on Schistosomiasis : Further Surveys in Mindanao. J. Philippine M. A. 25 : 417-433, September 1949).

Preventive measures taken before invasion of Leyte

By the middle of 1944, plans were being prepared for the recapture of the Philippines, with an initial landing to be made in Sarangani Bay in southern Mindanao on 15 November. This operation was to be followed by an airborne assault against Misamis Oriental in northwestern Mindanao on 7 December and by landings on Leyte on 20 December. In mid-September, it was decided to abandon the landings on Mindanao and, instead, to invade Leyte on 20 October. For security reasons, strictest secrecy was maintained about the change in plans. Consequently, medical personnel responsible for health problems encountered by task forces were not informed of the change in plans until a short time before the invasion. While these medical officers knew that schistosomiasis was endemic on Leyte, there was no real awareness of the danger that lay in the path of the invading troops. There was also, among persons responsible for the indoctrination of combat troops, a definite lack of information regarding the incidence of and dangers of acquiring schistosomiasis. In many instances, responsible medical and line officers who had received information concerning the disease either carried out no indoctrination of troops or, if they did attempt to indoctrinate their men, failed to leave any impression on them regarding the disease.²⁸

Either before or at the time of the landings on Leyte, several higher headquarters issued information and directives concerning schistosomiasis. Included were the following :

1. A letter from Headquarters, Sixth U.S. Army, dated 1 October 1944, giving a brief description of schistosomiasis, together with instructions concerning the dangers of using stream or pond water for bathing, laundering clothes, or drinking.

2. A standing operating procedure from Headquarters, Base K [at Tacloban, Leyte], dated 1 October 1944, stating that unit commanders would designate areas along streams for obtaining drinking water, for bathing, for laundering clothes, and for washing equipment and vehicles.

3. A technical memorandum from the Office of the Chief Surgeon, USAFFE (United States Army Forces, Far East), dated 21 October 1944, containing a description of schistosomiasis, pointing out the dangers which were present in an area of proved or doubtful endemicity, and recommending that in these areas the following precautions be adopted insofar as the military situation permitted: (1) Fresh water from ponds, ditches, or streams should not be allowed to touch the skin nor be ingested, and troops should

²⁸The consequences of a lack of awareness of the dangers of fresh water in areas endemic for schistosomiasis and of the failure to act to avoid infection are well illustrated by the episode which led to the high incidence of the disease in the British West African Force in 1944. More than 1,700 cases were diagnosed among troops who had engaged in amphibious training exercises and who had bathed in a fresh water lagoon at Epe, Nigeria. Before the exercises, no studies of the lagoon or of the native population were carried out, and medical officers of the division involved even regarded the risk of contracting schistosomiasis to be negligible. After the epidemic broke out, an investigation revealed that 100 percent of the natives who were examined had the disease and were releasing ova of S. haematobium in the urine.

avoid wading, bathing, or washing clothes in such water; (2) water should be obtained from newly driven casings reaching a depth of 10 or more feet; (3) where water must be drawn directly from streams, rapidly running water should be given preference as a source; and (4) all water should be hyperchlorinated (5 parts per million) for 30 minutes and then should be dechlorinated, and isolated detachments should boil all water used.

4. Warning issued to the XXIV Army Corps at the time of their landing at Leyte.

5. The Soldiers' Handbook of the Philippine Army, issued to troops before landings, briefly noting schistosomiasis and its occurrence in Leyte.

As an additional precautionary measure, two investigators were ordered to Leyte. These men, from the 19th Medical General Laboratory, Hollandia, New Guinea, and the 5th Malaria Survey Detachment, then stationed in New Guinea, landed on the island within the first 4 days of the fighting, with orders to initiate immediate surveys in the Leyte Valley to determine the distribution of the snail host of S. japonicum in surface waters and the infection rate in these mollusks, to identify reservoir hosts, and to investigate the incidence of schistosomiasis in the civilian population.²⁹

Preventive measures taken after invasion of Leyte

On 27 October 1944, 7 days after the invasion, copies of reports on the 6-month schistosomiasis survey that had been carried out by the Philippine Government on Leyte during 1940 and 1941 were obtained in Tacloban, Leyte, from the Provincial Public Health Office. These reports, published by Tubangui and Pasco in 1941, provided the information regarding S. japonicum on the island, but this was the first time these studies had been seen by those responsible for indoctrination in the prevention of schistosomiasis. It was soon evident to the investigators that the endemic area extended over the entire Leyte Valley. With the cooperation of members of the Provincial Public Health Office, they located breeding places of the molluscan host, Oncomelania quadrasi, and observed the characteristics and habitat of this snail. On the basis of the new information obtained, a report incorporating pertinent facts not previously available was prepared by the senior author and submitted to the Surgeon, Sixth U.S. Army, about 1 November 1944. A new directive concerning schistosomiasis was not prepared.

With the facts obtained from the 1940-41 survey reports and from Filipino health personnel, it was possible for the special investigators and members of malaria survey detachments who had arrived on Leyte early in the campaign to initiate surveys of the breeding places of O. quadrasi and to carry on microscopic examination of stools to determine infection rates in the civilian population. These studies were limited to the localities of Palo, Tacloban, and Tolosa. During these first weeks, survey work was often re-

²⁹Quarterly Report, Surgeon, Sixth U.S. Army, Southwest Pacific Area, 1 Oct. to 31 Dec. 1944.

stricted by combat activities in the area. In early December, the studies expanded as additional malaria survey detachments arrived and went to work. The officers of these units were informed on the appearance and habitat of O. quadrasi at a meeting held in late November.³⁰ This meeting was attended by the chief malariologist of the theater and the malariologists of the Sixth and Eighth U.S. Armies and Base K, and plans were drawn up for carrying on systematic field surveys. New information acquired through these surveys was to be used by combat and supply medical personnel to improve the indoctrination of troops already on the island and of newly arriving troops.

Significant contributions were made by the 5th, 6th, 34th, 41st, 205th, and 211th Malaria Survey Detachments. The 6th Malaria Survey Detachment was particularly active with a schistosomiasis educational program, in which the personnel prepared and distributed a large number of posters and erected warning signs along certain ditches in which O. quadrasi were found. A number of signs were also painted and erected by the 93d Malaria Control Detachment (fig. 4). As a result of the limited educational program, a few

FIGURE 4.-Warning sign posted by a malaria control detachment. Note Filipino woman washing clothing in a stream

³⁰Letter, Lt. Col. G. L. Orth. MC, Chief Malariologist, Army Service Command, to Brig. Gen. G. B. Denit, Chief Surgeon, USAFFE, 21 Nov. 1944.

commanding officers became highly conscious of the hazards of infection among men exposed to fresh water and strictly enforced the directives from higher headquarters. For example, the entire camp area of the 11th Airborne Division stretching along the coast for more than a mile was posted with warning signs.

Schistosomiasis was a disease relatively new to U.S. medical officers. Plans were made in December 1944 to treat a number of Filipino patients in the 118th General Hospital, Tolosa, Leyte. It seemed desirable to study the efficiency of various drugs, for example, antimony compounds, and to obtain as much information as possible before troops might require treatment as a result of exposure either in the Philippines or elsewhere in subsequent campaigns. This program was actively sponsored by the theater medical consultant.

In early December 1944, this medical consultant also planned for a survey of troops of the 21st Regiment, 24th Division, to determine whether or not any of the men had contracted schistosomiasis.³¹ In late December, before any infected Filipinos were hospitalized or troops surveyed, the disease made its dramatic appearance among U.S. soldiers.³²

Before December 1944, interest in schistosomiasis had been to a certain extent academic. It was felt by some Medical Department personnel that the disease would not be of military importance in Leyte. The various letters and memorandums which had been issued, it was assumed, would prevent outbreaks.

In spite of the precautions taken before and after the invasion to prevent schistosome infection in troops, information concerning the disease was not generally disseminated. Troops who were aware of the dangers of exposing themselves to fresh water tended to minimize the hazard or to ignore it almost completely. Out of the first 100 consecutive patients with schistosomiasis treated in the 118th General Hospital, only about 15 percent admitted ever having heard of the disease or of blood worms or flukes.³³

There were several reasons for the exposure of large members of U.S. troops to schistosome cercariae on Leyte. Some of the various memorandums and letters ordering precautionary measures failed to reach units until several weeks after their arrival on the island. Wording of other memorandums made them unclear. Some streams declared to be free of the snail host of S. japonicum later proved to be infested. Some troops, especially combat engineers engaged in building bridges, were required to enter streams and swamps and to remain partly immersed for considerable periods of time.

³¹Letter, Col. Henry M. Thomas, Jr., MC, to Chief Surgeon, U.S. Army Services of Supply, Southwest Pacific Area, 13 Dec. 1944.
³²Thomas, H. M., Jr., and Gage, D. P.: Symptomatology of Early Schistosomiasis Japonica. Bull. U.S. Army M. Dept. 4: 197-202, August 1945.
³³Billings, F. T., Jr.: Experiences of the U.S. Army Medical Department With Schistosomiasis Japonica in World War. II. [Official record.]

Other causes of exposure of U.S. troops included the desire of the soldiers to wash their clothing and to go swimming, even though they were warned that fresh water might be dangerous. Also, excessive emphasis had been placed on the dangers of the ricefields, and many soldiers were of the opinion that these fields and swamps, rather than streams and fresh water, were the main sources of the infection. It was only when wells were dug and showers installed that stream water began to lose its attraction. Exposure of troops while laundering clothes was not so great on Leyte as on other Pacific islands, since most of the laundry was done by civilians (fig. 5). If clothing was

FIGURE 5.-Filipinos washing clothing in grassy marsh. Molluscan host of S. japonicum, O. quadrasi, was abundant here.

completely dry when worn, there was no danger from infection by cercariae that might adhere to the fabrics.

Outbreak of schistosomiasis japonica

During the period from the latter part of November through December 1944, the first patients with schistosomiasis were admitted to hospitals. These patients suffered from urticaria, cough, abdominal pain, diarrhea, and fever, and often had high eosinophil counts. Though the disease may have been suspected by some ward officers, it was not recognized. The first diagnosis of schistosomiasis in the area was made not in Leyte but on Biak Island, at

the 132d General Hospital, on 23 December 1944. Eggs of S. japonicum were found in a liver biopsy specimen taken from a soldier who had been evacuated from Leyte.³⁴ The second case was diagnosed on 29 December at the 19th Medical General Laboratory. The patient was a wounded soldier transferred from Leyte. It was not until the following day, 30 December, that the first cases were diagnosed on Leyte at the 36th Evacuation Hospital. Many other cases were identified within the next few days, and, by the end of January 1945, the number totaled about 70. By 1 March, over 300 cases had been admitted to hospitals.³⁵

When the first cases of schistosomiasis were identified on Leyte, the hitherto academic interest of Medical Department personnel in the disease immediately changed to an acute apprehension of the possibility that a real epidemic might be developing. Ward officers became alert to the symptoms of the disease, and the hospital laboratories soon were swamped with stool specimens for microscopic study. At the same time, the malaria survey detachments redoubled their emphasis on field investigations.

A study of hospital records revealed that certain units were supplying a large percentage of the cases. This led to an investigation of the activities of personnel of the units, and it was apparent that swimming and bridge-repair operations probably accounted for the exposure of most of these men. In the 50th Engineer Combat Battalion, which eventually had 102 proved cases, bridge repair had led to the majority of the exposures (figs. 6 and 7). Among the detachment personnel of the 118th General Hospital, with about 75 proved cases, exposure came as a result of swimming. Swimming also accounted for proved cases of the disease in 144 of 560 men in an Australian Air Force construction squadron which had spent only 16 days on Leyte.³⁶ It became apparent early that the infection rate among infantrymen was relatively low. Totals compiled on 31 May 1945, for known cases among Eighth U.S. Army troops, the majority of which had been diagnosed in January and February, revealed that, out of 575 cases, 203 were from a small number of engineer battalions and 189 from numerous infantry units.³⁷

Preventive measures taken after outbreak

Combat operations on Leyte passed from Sixth U.S. Army control to that of the Eighth U.S. Army during the last week of December 1944. In early January, with schistosomiasis now a very real entity, new and stronger directives concerning its prevention and calling for the disciplining of offend-

³⁴Letter, Maj. Maxwell G. Berry, MC, Chief of Medical Service, 117th Station Hospital, to Commanding Officer, 132d General Hospital, 24 Jan. 1945, subject : Treatment and Disposition of Patients With Schistosomiasis. First indorsement thereto with inclosure : Schistosomiasis Japonicum, Report of a Case.
³⁵Monthly report of Malariologist, Office of the Surgeon, Base K, Southwest Pacific Area, to Commanding General, U.S. Army Services of Supply, 6 Mar. 1945.
³⁶Dakin, W. P. H., and Connellan, J. D.: Asiatic Schistosomiasis : An Outbreak in the Royal Australian Air Force. M.J. Australia 1: 257-265, 1 Mar. 1947.
³⁷Sullivan, R. R., and Ferguson, M. S. : Studies on Schistosomiasis Japonica : III. An Epidemiological Study of Schistosomiasis Japonica. Am. J. Hyg. 44: 324-347, November 1946.

FIGURE 6.-Bridge built by combat engineers. Tributaries of this stream drained marshes in which the molluscan host of S. japonicum was plentiful

ers, were issued by Headquarters, USAFFE, major commands in the Pacific, and subordinate commands. Typical was the letter issued on 22 January 1945 by the commanding general of Base K, the administrative headquarters for service units on Leyte not assigned to Army or Air Corps headquarters. This letter read in part:

1. Experience with this dangerous tropical blood fluke reveals that it is extremely common in this Base. The civilian population is heavily infected, and many cases have occurred in Army personnel, some of which have been fatal * * *.

* * * * * *

3. * * *. The following precautions will be observed: (a) All water used by troops will be obtained from approved water points * * *. This is meant to include water used for drinking, bathing, laundry, and washing of vehicles or floors. (b) Wading, bathing, and washing of clothing by troops in any fresh water river, swamp, pond, or rice field is prohibited * * *.

4. * * *. All unit commanders will inform their personnel of the contents of this directive, and will be held responsible for the rigid enforcement of the measures in paragraphs 3 a and b.

FIGURE 7.-Combat engineers repair bridge over a stream choked with water hyacinth. Molluscan host of S. japonicum was plentiful here.

Now that the Leyte campaign was ended, the majority of the units on the island were better established in camp areas; showers had been installed, and practically all fresh water for bathing and laundering was being obtained from wells. Vehicles were also being washed with water from wells. Bridge building was still being carried on, but engineers, now aware of schistosomiasis, were beginning to provide their personnel with rubber boots and flat-bottomed boats for work in water. However, in February it was still not unusual to see men swimming and washing clothing or vehicles in streams. When inquiries were made of these men, the majority pleaded ignorance of the disease and of the mode of infection.

During late January 1945, an intensive educational program got under way. The Chief, Professional Services, Office of the Surgeon, USAFFE, was largely responsible for the direction of this program. He insisted it be emphatically stressed to the troops that they must stay out of all fresh water. Excellent, coordination work was also done by the Malariologist, Office of the Surgeon, Base K. Posters were distributed by Base K and the Office of the Surgeon, XXIV Army Corps. Of special interest and value was a cartoon published by the 81st Infantry Division (fig. 8). Numerous roadside signs were prepared and posted by the 5th Malaria Survey Detachment. Short, pertinent items regarding the disease were brought to the attention of troops by means of the radio and unit newssheets. The malaria detachments were

FIGURE 8.-Cartoon dealing with schistosomiasis. Used in educational program for prevention of schistosome infection conducted by the Office of the Surgeon, 81st Infantry Division.

asked to report to unit commanders any personnel found washing vehicles or bathing in fresh water and to be active in disseminating information about schistosomiasis through personal contact.

There was some discussion among Medical Department personnel responsible for this educational program as to the advisability of placing warning signs along streams, ditches, or swamps in which the snail host had been found. It was feared by some that troops might assume that an unmarked stream was free from infection. By this time, field studies were beginning to show that streams could apparently be infested with cercariae at points a mile or more below the breeding areas of the snails, which in most cases were swamps or vegetation-choked streams that drained into rivers. Epidemiological studies of outbreaks in certain units whose activities were known forced the conclusion, in the absence of the actual collection of cercariae, that active larval worms could be carried long distances in moving water from the point at which they emerged from the snail host. This is probably the most important conclusion drawn from the Army studies of the epidemiology of schistosomiasis japonica. Similar conclusions were to be found in the litera-

ture,³⁸ but the hazard of infection in streams in the absence of the snail host had not been emphasized.

A very significant contribution to the educational program was made by two mobile laboratories that were equipped and sent from unit to unit by the Office of the Surgeon, Base K, to acquaint troops with the disease. Two enlisted men, one the driver and the other a man qualified to discuss the disease, accompanied each truck and gave demonstrations and lectures before thousands of troops during a period of about 4 months (fig. 9). Schistoso-

FIGURE 9.-Mobile laboratory and lecturer giving a demonstration on the prevention of schistosomiasis before a group of soldiers

miasis, or "schisto" as the disease was commonly known, became a byword with the troops in the field. The adoption of this term permitted the men to avoid use of a long word that was difficult to remember and pronounce. It was also much more appropriate than the term "snail fever" that was first proposed by the U.S. Navy and later used by the Office of the Surgeon General in the preparation of posters for distribution overseas (fig. 10).

³⁸(1) Egan, C. H.: An Outbreak of Schistosomiasis Japonicum. J. Roy. Nav. M. Serv. 22: 6-18, January 1936. (2) Taylor, A. W. : An Inquiry into the Origin of an Outbreak of Schistosomiasis Among Europeans at Kagoro, Northern Nigeria. West African M.J. 5: 61-62, April 1932. (3) Ferguson, M. S.: Schistosome Infection by Cercariae Distant From Snail Foci. Kuba 3: 86-87, April 1947.

FIGURE 10.-Photograph of War Department poster prepared at request of Office of the Surgeon General for distribution to Army units in Far East

The whole program of control of schistosomiasis in troops was a preventive one; that is, it stressed the avoidance of infested water. Control of the disease in the civilian population and in animals would be a long-term project involving snail control, proper disposal of feces, treatment of infected individuals, and destruction or treatment of reservoir hosts.

By April 1945, the number of new cases of schistosomiasis had dropped to a low level. The educational program and directives leading to strong command action were remarkably effective in limiting the number of new infections acquired in 1945. A study of case histories would seem to indicate that the majority of the exposures had occurred in late October and in November and December 1944. This was the period of combat operations, when troops had to go into infested waters in line of duty and when shower facilities for bathing were scarce. It was also the season of greatest rainfall in eastern Leyte, a period favorable for the multiplication of snails and for their infection by schistosome miracidia. These heavy rains probably served to flush out swamps and small vegetation-choked streams in which O. quadrasi was abundant, and live cercariae could have been transported in flooded rivers to locations where they were encountered by troops. Moreover, November and December were months during which those in command of troops were not yet keenly aware of the disease and most of the Medical Department personnel had only a hazy concept of schistosomiasis and did not believe that it would be of military importance in Leyte.

During January and February 1945, depending on the policy of the particular hospital, some patients were evacuated to the United States as soon as the diagnosis of schistosomiasis was made while others were evacuated after one course of treatment with an antimonial drug. Other patients were treated and held under observation for long periods on Leyte. Finally, in July 1945, the Surgeon, USAFFE, directed that all patients with schistosomiasis japonica be evacuated to the United States within a period of 120 days after the diagnosis had been established. The haphazard evacuation policy existing during the early weeks of the outbreak was seized upon by a few individuals as a possible means of getting home. Some of these men were known to have willfully exposed themselves to infection by swimming in streams considered dangerous. Others who were patients in hospitals for other causes were known to have attempted to purchase stools positive for S. japonicum, so that these fecal specimens could be submitted as their own.

Maj. Gen. Norman T. Kirk, The Surgeon General of the Army, indicated in a letter dated 26 March 1945 to the Surgeon, Headquarters, USAFFE, that schistosomiasis was considered to be a serious disease from the point of view of the patient but that, on the basis of information then available, it appeared unlikely that the disease would create a very great military problem. Among the hundreds of thousands of men who served in the Southwest Pacific, for either short or long periods during 1944 and 1945, 1,544 cases of schistosomiasis were diagnosed. It cannot be ascertained whether all these

cases occurred in Leyte. Relatively, this is a small number; however, in view of the fact that the average duration of hospitalization for schistosomiasis cases in the Philippines during 1945 was approximately 6 months, the disease assumed real military significance. Of further significance was the low morale of these infected men due to the long periods of hospitalization, the uncertainty of the medical officers as to the value of antimonial drugs being used, and the possibility that the disease might later assume a chronic phase. The apprehensiveness of the men with schistosomiasis could not be entirely confined to hospital areas; it carried over somewhat to healthy troops as well. This was particularly true of men who had been exposed to fresh water, either in line of duty or while bathing, and who had developed no clinical symptoms.

Investigations pointed toward control

Mention has been made of the field and laboratory studies carried out by the malaria survey detachments and special investigators during the early weeks of the Leyte campaign. Some useful information regarding S. japonicum was obtained by these workers both before and after the disease appeared in troops. However, it was difficult to coordinate the activities of these individual units, which were often widely separated and were under officers with varying degrees of training and interest in the problem of schistosomiasis. Coordination was also impeded by the fact that the units were assigned to Army Ground Forces, Army Air Corps, or Base K headquarters, and the investigators never knew when they might be alerted to move on to another island. In addition, most malaria survey detachments had other duties, such as making mosquito surveys and investigating sanitation conditions.

After the disease appeared, it became apparent that a group of interested persons should be assigned to work full time on the investigation of means of preventing further infection in troops. To do this, a broad study would have to be made of the whole schistosomiasis problem in Leyte. Finally, in February 1945, the 5th Malaria Survey Detachment was reassigned from the Eighth U.S. Army to Base K headquarters and was designated as a schistosomiasis research unit, with the privilege of acquiring necessary equipment not included on the regular table of equipment of malaria survey detachments. About this time, the malaria research unit formed in Australia in 1943 arrived on Leyte and turned its attention from problems of malaria to those concerning schistosomiasis japonica. These two units set up adjoining laboratories at the 118th General Hospital near Tolosa and carried on a joint investigational program until after the end of the war in the Pacific.

On 25 April 1945, the Subcommission on Schistosomiasis, Commission on Tropical Diseases, Army Epidemiological Board, arrived on Leyte from the United States.³⁹ A laboratory was set up in Tacloban. The members of the

³⁹See footnote 12, p. 54.

Subcommission contemplated a program of study embracing the field and laboratory observation of the biology of O. quadrasi, the schistosome infection in the snail host, the emergence and longevity of the cercariae in water, and field trials of molluscacides. Studies of the epidemiology of schistosomiasis japonica were to be carried out, reservoir hosts were to be identified, laboratory methods of diagnosing the disease were to be investigated, and the protective value of clothing was to be determined.⁴⁰

When the Subcommission on Schistosomiasis was formed in the United States, there was the distinct possibility that U.S. forces would not only invade Japan but also would make landings along the coast of China, where schistosomiasis is a serious problem, especially south of the Yangtze River. Consequently, the investigations to be undertaken by the Subcommission were not intended to relate solely to the schistosomiasis problem as it existed in the Philippines.

In May 1945, three naval officers comprising an epidemiological team from Naval Medical Research Unit No. 2, located on Guam, came to Leyte. Since only 16 proved cases of schistosomiasis had appeared among Navy personnel,⁴¹ no extensive investigations were planned by this group.

The Subcommission on Schistosomiasis, the Malaria Research Unit together with the 5th Malaria Survey Detachment, and the Navy epidemiological team each planned and carried on their own respective investigational programs. There was some imperfection in the collaboration of the three groups, but cooperative projects were developed by the Subcommission in association with the 5th Malaria Survey Detachment and the Malaria Research Unit and by one member of the Navy team in association with the Army research groups. The latter were most fortunate in having Lt. R. Tucker Abbott of the Navy team, an expert on mollusks, work with them, for until the time of Lt. Abbott's arrival on Leyte there had been no one who could identify snails found in the fresh waters of the island.

The Army and Navy groups remained on Leyte until after the war ended in September. In late October, some of the members of the Subcommission on Schistosomiasis and the commanding officer of the Medical Research Unit proceeded to Japan, where studies were made of the distribution of the disease and its intensity in the natives in endemic areas.⁴²

Early in 1945, when the members of the Medical Research Unit and 5th Malaria Survey Detachment, all of whom had been overseas for nearly 2 years, undertook intensive schistosomiasis investigations, they were handicapped by lack of access to the literature. Exchange of information between these investigators and research workers in the United States was severely restricted because of the security regulations in the Southwest Pacific Area. Even

⁴⁰Annual Report, Commission on Tropical Diseases, Army Epidemiological Board, 19 Apr. 1945?19 Apr. 1946.
⁴¹Hunt, A. R.: Schistosomiasis in Naval Personnel, a Report of Sixteen Cases. U.S. Nav. M. Bull. 45 : 407-419, September 1945.
⁴²See footnote 12, p. 54.

reports that could have been of little value to the enemy were routinely classified as "Secret," and consequently copies of these reports that were forwarded to Washington were given limited circulation. The arrival of the Subcommission on Schistosomiasis and the Navy epidemiological team provided those who had been in the field a long time an opportunity to become acquainted with schistosome research programs then in progress in the United States and also a chance to examine additional literature relating to blood flukes.

The results obtained by the schistosomiasis research groups demonstrated that, in spite of the handicaps encountered in a combat area, much can be accomplished by field investigations. These findings are incorporated in a series of papers, the most important of which are briefly summarized in following paragraphs.

Survey and diagnostic methods.-Studies were made, and illustrations were prepared of the eggs of S. japonicum from the newly laid stage, through the development of the mature egg containing a motile miracidium, and including the degenerating stage.⁴³ These studies were prompted by the difficulties that certain hospital laboratories encountered in attempting to diagnose the disease in patients whose stools did not contain mature eggs. In several instances, positive diagnoses were made on men who probably did not have the disease, when objects that were believed to be eggs were merely artifacts such as plant cells and oil droplets. An instance of such a series of mistaken diagnoses was the outbreak reported among the personnel of a station hospital who, although resident in an endemic area on Leyte, had never made real contact with infested water.⁴⁴ Recovery of the eggs of the parasite from the stool, through the use of standard techniques or modifications of them, was found to constitute the only method of specific diagnosis of schistosomiasis japonica.⁴⁵

Serologic studies revealed that in intradermal tests antigen prepared from adults of S. mansoni gave a high percentage of positive reactions in Filipinos with chronic cases but negative results in recently infected U.S. soldiers. Whereas a high percentage of proved cases of schistosomiasis japonica in U.S. military personnel were positive on the flocculation test, 100 percent of the studied chronic cases in Filipinos were positive to this test. The formol-gel tests on blood serums from U.S. soldiers were all nega-

⁴³(1) Bulletin, Office of the Chief Surgeon, Headquarters, Army Forces, Pacific, 10 June 1945, subject : Guide for the Identification of the Ova of Schistosoma japonicum, pp. 1-6. (2) Faust, E. C.: The Diagnosis of Schistosomiasis Japonica. II. The Diagnostic Characteristics of the Eggs of the Etiologic Agent Schistosoma japonicum. Am. J. Trop. Med. 26: 113-123, January 1946.
⁴⁴( 1 ) Leavitt, S. S., and Beck, O. H.: Schistosomiasis Japonica ; A Report of Its Discovery in Apparently Healthy Individuals. Am. J. Trop. Med. 27: 347-356, May 1947. (2) Quarterly Report, Surgeon, 13th Station Hospital, Southwest Pacific Area, 1 April-30 June 1945.
⁴⁵(1) Bang, F. B., Hairston, N. G., Graham, O. H., and Ferguson, M. S.: Studies on Schistosomiasis Japonica. II. Methods of Surveying for Schistosomiasis Japonica. Am. J. Hyg. 44: 315?323, November 1946. (2) Faust, E. C., Wright, W. H., McMullen, D. B., and Hunter, G. W., III: The Diagnosis of Schistosomiasis Japonica. I. The Symptoms, Signs and Physical Findings Characteristic of Schistosomiasis Japonica at Different Stages in the Development of the Disease. Am. J. Trop. Med. 26: 87-112, January 1946. (3) Faust, E. C., and Ingalls, J. W.: The Diagnosis of Schistosomiasis Japonica. III. Technics for the Recovery of the Eggs of Schistosoma Japonicum. Am. J. Trop. Med. 26 : 559-584, September 1946.

tive; in contrast, a fairly high percentage of serums from Filipinos with chronic cases reacted positively to this test.⁴⁶

A liver index, the average enlargement of the liver in children ranging in age from 5 to 15 years, was found to be useful in assessing the endemicity of schistosomiasis japonica in an area and in giving a clue to the health of that community. Failure to find the molluscan host in an area was no evidence that the disease was not present, but the infection rate in reservoir hosts-for example, dogs, pigs, and rats-proved to be a good indicator that the people had schistosomiasis japonica.

Epidemiology.-Field studies revealed new areas of infection on Mindoro and Mindanao, Philippine Islands.⁴⁷

A detailed study of the infection in the 50th Engineer Combat Battalion and its relation to activities involving contact with fresh water was undertaken in January 1945. It was revealed that bridge building and repair were responsible for the majority of the 102 cases of the disease. Swimming was not an important factor. It was found that an eosinophil survey of the men in the battalion served as a useful case finder. One of the most important conclusions drawn from this study was that a stream may be infective at least a mile below the point where infected snails are located. This is possible since the cercariae come to the top of the water, attach to the surface film, and therefore can be carried downstream. Consequently, failure to find the snail host at a certain point in a stream is no criterion of safeness for swimming or activities involving contact with water.

Molluscan intermediate host.-Laboratory studies on the hatching of eggs of S. japonicum containing mature miracidia revealed that light has no effect on the process and that there was no diurnal or nocturnal cyclic frequency in the hatching rates. Best hatching was obtained when feces were comminuted in river water having a pH of 7.6.⁴⁸ It was likewise observed that the largest number of cercariae were released from infected O. quadrasi when the mollusks were placed in river water having a pH of 7.6. Cercariae were liberated cyclically, being discharged on 2 or 3 successive nights between 9 and 11 p.m., after which few larvae would emerge over the next 2 or 3 days.⁴⁹

Studies in prevention.-The eggs of O. quadrasi were found to be laid singly. They are cemented to the surface of damp, decaying vegetation and

⁴⁶Wright, W. H.. Bozicevich, J., Brady, F. J., and Bauman, P. M.: The Diagnosis of Schistosomiasis Japonica. V. The Diagnosis of Schistosomiasis Japonica by Means of Intradermal and Serological Tests. Am. J. Hyg. 45: 150-163, March 1947.
⁴⁷Hunter, G. W., III, Dillahunt, J. A. and Dalton, H. C.: The Epidemiology of Schistosomiasis Japonica in the Philippine Islands and Japan. I. Surveys for Schistosomiasis Japonica on Mindoro, P.I. Am. J. Trop. Med. 30: 411-429, May 1950.
⁴⁸Ingalls, J. W., Jr., Hunter, G. W., III, McMullen, D. B., and Bauman, P. M. : The Molluscan Intermediate Host and Schistosomiasis Japonica. I. Observations on the Conditions Governing the Hatching of the Eggs of Schistosoma japonicum. J. Parasitol. 35 : 147-151, April 1949.
⁴⁹Bauman, P. M., Bennett, H. J., and Ingalls. J. W., Jr. : The Molluscan Intermediate Host and Schistosomiasis Japonica. II. Observations on the Production and Rate of Emergence of Cercariae of Schistosoma japonicum From the Molluscan Intermediate Host, Oncomelania quadrasi. Am. J. Trop. Med. 28: 567-575, July 1948.

are covered with a layer of fine sand grains and organic matter. The biology and life cycle of the mollusk were carefully studied, and it was determined that this snail may reach maturity in from 4 to 5 months.⁵⁰ Laboratory tests showed that the eggs of O. quadrasi were killed rapidly by two dinitro compounds, dinitro-ortho-cyclohexylphenol and its dicyclohexylamine salt.

Field studies were conducted on the molluscacidal properties of 19 chemicals. Results indicated that the two dinitro compounds mentioned were promising.⁵¹ After the war, these experiments on molluscacides were continued in Japan. Any program of snail control is faced with the problems of the cost and application of materials and the effect of the molluscacide on vegetation and animal life in the water. It was evident from the beginning that control of schistosomiasis japonica through snail destruction would be a long-term project and therefore not a practical military procedure.

The cercaricidal effects of the Army's routine water chlorination methods were tested in the laboratory, and it was found that these procedures provided an ample margin of safety against the ingestion or penetration of live cercariae. If water had a residual chlorine strength of 1 p.p.m. after one-half hour, it was safe for drinking or bathing even though taken from an infested stream.

In Leyte, the question arose as to whether ocean bathing near the mouths of rivers carrying water from marshes and streams infested with O. quadrasi constituted a health hazard. It was determined that sea water with a 3-per?cent salinity killed cercariae of S. japonicum in less than 3 minutes and therefore was safe for bathing. Areas near the mouth of a river where sea water is diluted to less than 1.5-percent salinity were considered to be potentially dangerous.⁵²

Information was required by the Army regarding any preparation that could be applied to the skin to protect against the penetration of cercariae; for example, for use on the hands of men who were required to work in water. In vitro tests and in vivo tests with rats and mice suggested that troops could be afforded this protection by skin applications of the liquids, dimethyl

⁵⁰McMullen, D. B. : The Control of Schistosomiasis Japonica. I. Observations on the Habits, Ecology and Life Cycle of Oncomelania quadrasi, the Molluscan Intermediate Host of Schistosoma japonicum in the Philippine Islands. Am. J. Hyg. 45: 259-273, May 1947.
⁵¹( 1 ) McMullen, D. B., and Graham, O. H.: The Control of Schistosomiasis Japonica. II. Studies on the Control of Oncomelania quadrasi, the Molluscan Intermediate Host of Schistosoma japonicum in the Philippine Islands. Am. J. Hyg. 45: 274-293, May 1947. (2) McMullen, D. B., Komiyama, S., Ishii, N., Endo-Itabashi, T., and Mitoma, Y. : Results Obtained in Testing Molluscacides in Field Plots Containing Oncomelania nosophora, an Intermediate Host of Schistosoma japonicum. Am. J. Trop. Med. 31 : 583-592, September 1951. (3) McMullen, D. B., Komiyama, S., Ishii, N., Endo-Itabashi, T., Ozawa, K., Asakawa, T., and Mitoma, Y.: The Use of Molluscacides in the Control of Oncomelania nosophora, an Intermediate Host of Schistosoma japonicum. Am. J. Trop. Med. 31 : 593-604, September 1951. (4) Hunter, G. W., III, Ritchie, L. S., Freytag, R. E., Pan, C., and Potts, D. E.: "Operation Santobrite," a Schistosome Snail Eradication Program in Japan. J. Parasitol. 37 : 31-32, November 1951 (Supp.).
⁵²Ingalls, J. W., Jr. : The Control of Schistosomiasis Japonica. III. Studies on the Longevity of Cercariae of Schistosoma japonicum in Saline Solutions. J. Parasitol. 32: 521-524, December 1946.

phthalate, dibutyl phthalate, benzyl benzoate, Rutgers 612, and Indalone, or salves containing these insect repellents.⁵³

The protective value of military clothing required investigation. The protection afforded by rubber boots or waders to men who entered infested water was obvious. It was known by the Japanese that domestic animals could be protected from schistosome larvae by providing them with waterproof leggings or a double layer of cotton cloth with a mesh not more than 100 microns.⁵⁴ In vitro tests and in vivo tests with rats and mice suggested that all types of Army uniform cloth would afford considerable protection to the wearer. Old and worn uniform fabrics afforded less protection than new fabrics.⁵⁵

Army uniform clothing materials, when impregnated with the insect repellents dimethyl phthalate, dibutyl phthalate, benzyl benzoate, or emulsions containing one or more of these substances, were highly protective to animals. Some of the chemically treated materials continued to afford protection after several washings or after days of continuous soaking in water.⁵⁶

It was concluded, from the tests on applications to the skin and on impregnation of fabrics, that military personnel who had to enter water would be afforded a great degree of protection from schistosome cercariae if their hands were smeared with insect repellent or with salves incorporating a repellent, and if they wore chemically treated uniforms and socks and tucked trousers into the combat boots.

Treatment.-In any extensive study pointed toward the prevention of a disease, control through treatment of infected individuals should be considered, and the effect of a drug on the causative agent should be ascertained. The guinea pig was selected as an experimental animal, since the pathological pattern of schistosomiasis japonica in this animal was found to be similar to that in man. Fuadin, tartar emetic, and Anthiomaline were tested as chemotherapeutic agents. The effects of the drugs on the adult worm was first to cause the degeneration of the yolk glands in the female and then of the ovary and, finally, a shrinking of the whole worm. Treatment beyond 4 to 6 weeks killed large numbers of worms. The drugs had no effect on the eggs. Relapses occurred in the experimental animals and were due to a recovery by the females of their ability to produce eggs and

⁵³(1) Ferguson, M. S., Graham, O. H., Bang, F. B., and Hairston, N. G. : Studies on Schistosomiasis Japonica. V. Protection Experiments Against Schistosomiasis Japonica. Am. J. Hyg. 44: 367-378, November 1946. (2) Wright, W. H., Bauman, P. M., and Fry, N. H. : The Control of Schistosomiasis Japonica. VII. Studies on the Value of Repellents and Repellent Ointments as a Protection Against Schistosomiasis Japonica. Am. J. Hyg. 47: 44-52, January 1948.
⁵⁴Faust, E. C., and Meleney, H. E. : Studies on Schistosomiasis Japonica. Am. J. Hyg., Monographic Series, No. 3, 1924.
⁵⁵Hunter, G. W., III, Bennett, H. J., Fry, N. H., See, J., and Greene, E.: The Control of Schistosomiasis Japonica. V. Studies on the Penetration of Various Types of Unimpregnated Uniform Cloth by Cercariae of Schistosoma japonicum. Am. J. Trop. Med. 29: 723-737, September 1949.
⁵⁶Wright, W. H., Bauman, P. M., and Fry, N.: The Control of Schistosomiasis Japonica. VI. Studies on the Chemical Impregnation of Uniform Cloth as a Protection Against Schistosomiasis Japonica. Am. J. Hyg. 47: 33-43, January 1948.

return of adult female worms from the liver to the mesenteric veins.⁵⁷ It was concluded that relapse in man following treatment is nothing more than the recovery of reproductive functions by a surviving worm when the concentration of a drug is no longer damaging to it. These relapses may occur within a few weeks.⁵⁸ That adult schistosomes can recover from the effects of antimonial drugs (Fuadin and tartar emetic) and be productive of viable eggs 5 years later was demonstrated in followup studies of a group of U.S. Army veterans who had acquired schistosomiasis japonica in the Philippines. In a carefully studied group of five individuals, proved to have had the disease, four were demonstrated by rectal biopsy to be infected after this lapse of time. One man had had six courses of antimonial treatment during 1945. This continued egg productivity of S. japonicum for more than 5 years had been demonstrated similarly in untreated monkeys experimentally infected in Leyte and Japan in 1945 and brought to the United States for long-term study of the infection.⁵⁹ The fact that human beings, and possibly the reservoir hosts, may retain their infection for several years emphasizes the necessity of preventing feces of infected people and animals from reaching fresh water in areas where the appropriate snail host exists but where, as yet, schistosomiasis has not been introduced.

Directive on control

With the end of the war in early September 1945, preparations were made for occupation troops to proceed to Japan. In this connection, a directive, Circular No. 68, concerning the control of schistosomiasis japonica was issued by Headquarters, United States Army Forces, Pacific, on 11 September 1945. In addition to giving information about known areas of the disease in the Japanese islands, defining responsibility of unit commanders for indoctrination of troops, and ordering disciplinary action against violators of regulations pertaining to swimming, bathing, and so forth, in fresh water, the circular ordered the use of protective measures suggested in the investigational studies described. Bathing in sea water was to be permitted only when the salt content was 3 percent or above. Troops whose work required exposure to infested water were to wear uniforms made from cloth found to provide a barrier to cercariae and were to tuck their trousers into the combat boots. It was also stated that the protective value of the

⁵⁷Bang, F. B., and Hairston. N. G.: Studies on Schistosomiasis Japonica. IV. Chemotherapy of Experimental Schistosomiasis Japonica. Am. J. Hyg. 44: 348-366, November 1946.
⁵⁸(1) Letter, 5th Malaria Survey Detachment and Medical Research Unit, to The Surgeon General, 25 June 1945, subject: Report No. 5 : Reappearance of Ova in the Feces of Schistosomiasis Patients After Fuadin Treatment. (2) Most, H., Kane, C. A., Lavietes, P. H., Schroeder, E. F., Behm, A., Blum, L., Katzin, B., and Hayman, J. M.: Schistosomiasis Japonica in American Military Personnel : Clinical Studies of 600 Cases During the First Year After Infection. Am. J. Trop. Med. 30: 239-299, March 1950.
⁵⁹(1) Liu, C., and Bang, F. B.: Report to Veterans Administration. A Followup Study of Veterans Infected With Schistosoma japonicum. Five Years Previously. 1950 (unpublished). (2) Liu, C., and Bang, F. B.: The Natural Course of a Light Experimental Infection of Schistosomiasis Japonica in Monkeys. Bull. Johns Hopkins Hosp. 86: 215-233, April 1950.

clothing is enhanced by impregnation with insect repellent and that applications of insect repellent were to be made to the hands of those who were required to work in fresh water.

CONCLUSIONS AND SUMMARY

Down through the ages, military operations have been responsible many times for the exposure of troops to water containing schistosome cercariae; for example, in the crossing of streams and during the building or repair of bridges. Infested water was probably often used for drinking purposes. However, in view of the U.S. Army experience with schistosomiasis in the Philippines during World War II, the writers estimate that the majority of the cases of the disease acquired by soldiers in former times resulted from exposures while they bathed in or drank infested waters. Thus, if the means by which schistosomiasis was contracted had been known and the knowledge could have been applied, most of the infections could have been prevented.

When World War I broke out in 1914, the life history of S. japonicum was known. By 1915, the life cycles of S. mansoni and S. haematobium had also been elucidated. From then on, if troops were properly indoctrinated, there could be little excuse for their acquiring schistosomiasis as a result of swimming and the ingestion of untreated water. That schistosomiasis is a preventable disease is borne out by the experience of the Australians and British in the Middle East early in World War I. In Egypt and Mesopotamia, exposure was largely through swimming, sometimes in spite of repeated warnings regarding the dangers of entering fresh water. That schistosomiasis is a preventable disease in military forces was stated by Leiper, on the basis of his studies in Egypt in 1915.⁶⁰ He wrote: "With the information at the disposal of troops, bilharziasis should now be treated as one of those diseases for which the individual is mainly, if not entirely, personally responsible." However, the exposures that led to the infection of more than 1,700 men in the British West African Force in 1944 were apparently not the responsibility of the individual soldier. The important point to consider here is that the infections could have been prevented.

The importance of prevention of schistosome infections in troops is emphasized by the facts that there is no drug known to be prophylactic for schistosomiasis and that chemotherapeutic agents in current use are inadequate.⁶¹ The pathological consequences that may stem from the presence of living schistosomes in the blood vessels over a number of years also give emphasis to the importance of developing prophylaxis.⁶²

In connection with any military operation there are factors which tend to modify tile preventability of a disease such as schistosomiasis. Changes

⁶⁰Leiper, R. T. : Report on the Results of the Bilharzia Mission in Egypt, 1915. J. Roy. Army M. Corps 30: 235-260, March 1918.
⁶¹See footnote 58(2), p. 78.
⁶²See footnote 59(1), p. 78.

in tactics, military reverses, unavoidable accidents, the loss of protective equipment, and so forth, can make the amount of contact with infested water unpredictable. However, a study of the activities of the large number of combat engineers who became infected while building or repairing bridges on Leyte, work that called for long periods of exposure, indicated that most, if not all, of their disease could have been prevented if rubber boots, waders, flat-bottomed boats, and protective applications for the hands had been provided.⁶³ The length of time spent in infested water and the amount of clothing worn by the individual were found to be very important. Eight men from a medical unit who went swimming in a stream on Leyte for only half an hour all became infected. In contrast, of the thousands of fully clothed infantrymen who must have waded in streams, swamps, and flooded ricefields in the Leyte Valley, only a relatively small number developed clinical schistosomiasis. These observations suggest that clothing, even though not impregnated with chemicals, is highly protective against cercariae. The value of clothing in preventing infection was suspected in China by Laning even before the cercarial stage of S. japonicum had been identified,⁶⁴ and the Japanese have long recognized that protection is afforded by clothing.

When preparations are being made for operations in an area endemic for human schistosomes, knowledge of the distribution and intensity of the disease existing there is most important. The degree to which medical officers are aware of the available facts determines in great measure the success attending efforts to indoctrinate troops concerning the disease and its prevention. The medical officer has the important responsibility of seeing to it that the line officers with whom he is associated become keenly aware of the preventability of schistosomiasis; to accomplish this, he must be thoroughly familiar with the disease. Finally, preparations for a military operation in an endemic area should include plans on the part of medical personnel for conducting field research on schistosomiasis and its control.

Good schistosomiasis discipline on the part of troops demands an intensive educational program through which the men become adequately informed as to the dangers of exposure to fresh water in endemic areas. This training would require use of the varied mediums of communication; for example, printed matter, posters, films, lectures, demonstrations, the radio, and television. Troops must become thoroughly familiar with the slogan, "In Endemic Territory Keep Out of All Fresh Water." They must learn that under no consideration should they bathe in or drink fresh water from a stream. Responsible officers must realize that men should not be required to wade or work in water unless the exposed parts of the body are fully protected. In any educational program concerning the dangers of acquiring schistosomiasis and the means of preventing infection, the harmful effects of the disease must be stressed, and a little overemphasis is required. This will

⁶³See footnote 37, p. 65.
⁶⁴Laning, R. H.: Schistosomiasis on the Yangtze River, With Report of Cases. U.S. Nav. M. Bull. 8: 16-36, January 1914.

bea matter of concern to those who may already have acquired the disease and maycause some to become overly anxious, as was the case among U.S. soldiers whowere being treated for schistosomiasis in hospitals on Leyte.⁶⁵ However, aneffective educational program is essential, since it is concerned with thehealth and fighting capacity of the combat force in general.

Investigations onschistosomiasis carried on in the field during a military operation would ofnecessity be mainly concerned with prevention of the disease and treatment ofinfected troops. Since, in schistosome infection, there is a long period betweenthe time of exposure and the appearance of eggs in the feces, large numbers ofsoldiers could be infected before the disease was diagnosed. Therefore, sinceresearch requires time to yield results, field investigations, if they are to beuseful, must be pursued energetically from the time the troops enter an endemicarea. Because it has been amply demonstrated that the absence of the snail hostof schistosomes is no proof that the water in a stream or body of water is safe,investigators must make careful surveys to determine the breeding places andincidence of infection of the molluscan host. Studies on improved protectivemeasures for those who must come in contact with fresh water should be pursuedboth at home and in the field. This would also involve the search for an orallyadministered drug that is prophylactic for schistosome infection. Likewise,investigations on improved diagnostic methods, for example, for the recoveryof ova in stool specimens and serologic tests, would be necessary. Finally,there should be a continuing search for an adequate chemotherapeutic agent totreat those who might become infected.

As a result of World War II,approximately 2,500 cases of schistosomiasis were recorded for the U.S. Army.Approximately 850 of these infections were S. mansoni in Puerto Rican soldierswho had acquired blood flukes at home before entering military service. Onlyabout 20 cases of infestation with S. haematobium were identified in U.S.soldiers. These 20 soldiers became infected in 1943 during the North Africancampaign. An epidemic of schistosomiasis japonica developed in the Philippines,due to infections acquired on Leyte late in 1944 and early in 1945; 1,661 casesof this disease were diagnosed for the entire Pacific area. In addition, it hasbeen shown that, of the U.S. prisoners of war interned in southern Mindanao,120 or more contracted schistosomiasis japonica.

With the exception of troopswho acquired their infection in Puerto Rico and the prisoners of war who wereforced to work in infested water, U.S. troops were exposed to schistosomecercariae largely through swimming and other noncombat activities. Probably notmore than 10 percent of the infections resulted from combat activities.Therefore, in the light of the experience on Leyte, it may be concluded that, inmilitary forces, schistosomiasis is largely a preventable disease.

⁶⁵Frank, J. D.: Emotional Reactions of American Soldiers to an Unfamiliar Disease.Am. J. Psychiat. 102 : 631-640. March 1946.

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