History

CHAPTER III

Hookworm

Clyde Swartzwelder, Ph. D.

HISTORICAL NOTE

During World War I, there was no indication of acquisition of hookworm infection in oversea troops.¹ This conclusion was based upon a survey of 1,200 oversea and 300 home service troops in the U.S. Army. The oversea troops included men who had seen service mainly in France, with the exception of a few who had served on the Mexican border. Before World War II, oversea campaigns in the tropics were confined mainly to small-scale operations in Central America, Cuba, the Philippines, and Puerto Rico. Specific information concerning the military significance of hookworm infections in these campaigns appears to be lacking. Castellani² reported that hookworm infection did not constitute a problem in Italian troops during the Italo-Ethiopian War.

The two species of hookworm which produce intestinal infection in men are Nectar americanus and Ancylostoma duodenale. The American hookworm, N. americanus, occurs in the Southern United States, the Caribbean Islands, Central America, the northern part of South America, central and south Africa, southern Asia, Melanesia, and Polynesia. It is not endemic in Europe. The Old World hookworm, A. duodenale, has a geographic distribution which includes southern Europe, the north coast of Africa, northern India, northern China, and Japan. A. duodenale is not endemic in the United States. An assessment of the medicomilitary significance of hookworm infection during World War II, when U.S. Army troops were stationed in many of the aforementioned oversea areas, must be based upon the number of infections acquired, their clinical significance, and the possibility of troops` having implanted species of hookworm in areas where these species had not previously been endemic.

¹(1) Kofoid, C. A., Kornhauser, S. I., and Plate, J. T.: Intestinal Parasites in Overseas and Home Service Troops of the U.S. Army, With Especial Reference to Carriers of Amebiasis. J.A.M.A. 72: 1721-1724, June 1919. (2) The Medical Department of the United States Army in the World War. Washington: U.S. Government Printing Office, 1928, vol. IX, pp. 529-549.
²Castellani, A.: Medical Aspects of the Italo-Ethiopian War, October 3, 1935-May 9, 1936. Mil. Surgeon 81: 1-16, July 1937.

INCIDENCE OF HOOKWORM INFECTION IN WORLD WAR II

During World War II, large-scale military operations were conducted by U.S. Army troops for the first time in such tropical areas as Africa, India, China, and the South Pacific, where hookworm infection is heavily endemic. Large numbers of troops were exposed to this infection as they slept in foxholes, crawled through the jungle, occupied native villages, or otherwise came into intimate contact with soil previously contaminated by the excreta of infected inhabitants. The geographic areas in which the troops were deployed and the nature of combat during World War II resulted in exposure of many soldiers to hookworm infection.

Preliminary data indicated that during the years 1942 through 1945 there were 22,238 admissions to hospital and quarters for the treatment of hookworm infection (table 3). The number of admissions for hookworm infection increased from 2,526 in 1942 to 11,060 in 1945. This increase is probably explained by the expansion of the services and by the presence of a larger number of troops in tropical areas during the latter part of the war. The major increase in the number of admissions for hookworm infection was in the oversea forces. The number of admissions in the continental United States remained relatively constant except for the year 1944 in which admissions for these infections were fewer than in the preceding and following years. Since many troops were native residents of the Southern United States, where N. americanus is endemic, some of the hookworm infections undoubtedly were acquired before entrance into military service. Also, some infections acquired by individuals overseas probably were diagnosed on their return to the United States. The admission rates shown in table 3 support the view that the majority of hookworm infections were acquired in oversea areas. The rate for continental United States troops for the period from 1942 through 1945 was 0.53. In contrast, the rate for forces in oversea theaters was 1.35.

Data on admissions in oversea areas for 1944 (table 3) indicate that the Central and South Pacific and the Southwest Pacific areas, Latin America, and the Mediterranean and China-Burma-India theaters reported the largest numbers of cases, respectively. Areas with the highest admission rates per 1,000-man strength were Latin America, the Central and South Pacific, the Southwest Pacific, and the China-Burma-India theater, respectively. No deaths attributable to hookworm were reported in U.S. Army troops.

The total number of admissions for hookworm infection, 22,238, and the admission rate of 0.87 per 1,000 average strength for all Army troops (table 3) indicate a relatively low incidence of infection. This interpretation seems justifiable in view of the large number of troops sent to the tropics and the nature of their military activities which frequently resulted in unavoidable exposure. This appraisal seems more tenable when it is realized that these figures include some hookworm infections in persons who resided in the Southern United States before military service and in troops from Latin America.

TABLE 3.-Admissions for hookworm infection in the U.S. Army, by theater or area and year, 1942-45

Theater or area	1942-45		1942		1943		1944		1945
Theater or area	Number	Rate	Number	Rate	Number	Rate	Number	Rate	Number	Rate
Continental United States	7,783	0.53	2,201	0.83	2,258	0.44	1,249	0.31	2,075	0.71
Overseas:
Europe	382	.09	1	.01	41	.15	130	.08	210	.09
Mediterranean¹	264	.18	---	---	50	.11	179	.28	35	.10
Middle-East	27	.18	1	.17	8	.15	13	.28	5	.12
China-Burma-India	737	1.68	---	---	44	1.11	178	1.06	515	2.33
Southwest Pacific	8,207	4.47	15	.21	1,031	5.43	1,161	2.15	6,000	5.79
Central and South Pacific	3,201	2.55	58	.38	266	.91	1,217	2.77	1,660	4.42
North America²	138	.28	8	.08	24	.12	96	.74	10	.15
Latin America	1,469	3.85	242	2.37	341	2.82	361	4.21	525	7.21
Total overseas³	14,455	1.35	325	.55	1,806	1.07	3,339	.87	8,985	1.93
Total Army	22,238	.87	2,526	.78	4,064	.59	4,588	.59	11,060	1.46

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

Surveys of Troops for Hookworm Infection

There is much evidence that there was an active interest in the prevention of hookworm infection in troops, in the assessment of its military significance during the war, and in the minimization of the possibility of implanting A. duodenale in the United States where this species was not endemic. Numerous surveys were conducted among oversea and repatriated troops and among natives who represented reservoirs of infection and who were living near troop concentrations. A few of these are cited to indicate the nature of the hookworm problem. Apparently, all surveys of troops for hookworm infection utilized a flotation technique for detection of the organism. Usually, the zinc sulfate flotation method was employed.

Most and others³ reported an 11.5-percent prevalence of hookworm infection in 2,500 patients at Moore General Hospital, a tropical disease hospital at Swannanoa, N.C., among men who had returned from service in various Pacific islands. In contrast, prevalence of 6.2 percent was found in 4,300 men who had seen service only in the United States. Sixty-five percent of 169 infections, in which the species of hookworm was determined after treatment, were due to A. duodenale. The higher incidence of infection in troops with oversea service was believed to be largely due to A. duodenale. Hookworm

³Most, H., Hayman, J. M., Jr., and Wilson, T. B.: Hookworm Infections in Troops Returning From the Pacific. Am. J.M. Sc. 212: 347-350, September 1946.

infections in 100 malarial and surgical cases studied were subclinical in nature and did not represent hookworm disease.

A survey of hookworm infection in 4,000 male separatees at Fort McPherson, Ga., conducted under the auspices of the Tropical Disease Control and Laboratories Branch, Office of the Surgeon General,⁴ revealed a prevalence of 13.5 percent in troops with oversea service, in contrast to 7.5 percent in those with service in continental United States only. Very few infected troops had egg counts exceeding 5,000 per gram. The prevalence of hookworm infection in troops who served in the following theaters was as follows: European theater, 13.8 percent; Pacific, 13.0 percent; China-Burma-India theater, 11.3 percent; and Western Hemisphere tropics, 7.4 percent. Among troops who served in the European theater and in the Pacific areas, the incidence was 12.7 percent.

Prevalence of 39.2 percent hookworm infection in the 13th Engineer Battalion, 7th Division, on Okinawa, was reported.⁵ This organization had previously been in combat on Leyte. Rogers and Dammin⁶ reported that, although they had no reliable data on the actual incidence of hookworm infection among troops in north Burma during the summer and fall of 1944, the amount of infection of troops who served in forward areas there must have been considerable. A relatively acute syndrome of abdominal pain, anorexia, nausea, vomiting, diarrhea, and weight loss was observed in soldiers who had high eosinophilia and hookworm infection. A. duodenale infections predominated. The severity of clinical symptoms was considered disproportionate to the worm burden which was judged to be small in most cases. A survey of intestinal parasites of troops in the 32d Division in New Guinea, conducted in 1943, revealed an increasing prevalence of 5.8 percent in April, 13.5 percent in May, 12.7 percent in June, 18.1 percent in July, and 17.5 percent in August.⁷

Hookworm infection in the South Pacific appeared to have been acquired largely during combat.⁸ The extent of infection among troops was in direct proportion to the length of the time they had spent in combat. It was increased among those who had occupied native villages and captured enemy bivouac areas. As an example, an infantry division which served in both the Guadalcanal and the New Georgia campaigns had a much higher incidence than divisions which had battle experience only in the latter campaign. In combat, troops lived on the ground and slept in foxholes. Clothing was damp most of the time from the wet foxholes, rain, or perspiration. Bathing was

⁴Survey of Intestinal Parasites in Soldiers Being Separated From Service. Bull.U.S. Army M. Dept. 6: 259-262, September 1946.
⁵Medical Bulletin No. 19, Office of the Surgeon, Headquarters, Army Service Command I, Okinawa, 17 Sept. 1945.
⁶Rogers, A. M., and Dammin, G. J.: Hookworm Infection in American Troops in Assam and Burma. Am. J.M. Sc. 211: 531-538, May 1946.
⁷Report, 3d Medical Laboratory, August 1943, subject: Survey of Intestinal Parasites of the 32d Division.
⁸(1) Liebow, A. A., and Hannum, C. A.: Eosinophilia, Ancylostomiasis, and Strongyloidosis in the South Pacific Area. Yale J. Biol. & Med. 18 : 381-403, May 1946. (2) Hookworm Infection in South Pacific Area. Bull. U.S. Army M. Dept. 4: 372-373, October 1945.

impossible for periods as long as 30 days. Frequently, no change of clothing was possible. Socks were issued on occasion, but in 2 or 3 hours they were wet. Shoes deteriorated rapidly because of the constant dampness. Feces were disposed of by digging individual holes with entrenching tools; some deficiency was noted in this respect. It was to be expected that infantry troops which had the most intimate foxhole contact with the soil would have the highest incidence. The stretcher bearers of medical detachments of infantry battalions had a similarly high rate of infection. The incidence in headquarters, field artillery, and service and garrison troops was lower than in infantry and combat medical troops.

The hookworm burden among troops generally was relatively light, as indicated by the fact that Stoll egg counts averaged between four and eight thousand eggs per cubic centimeter. The majority of infected individuals made no complaints of symptoms. Evidence of acquisition of hookworm infection in troops in Pacific islands was also reported by Zarrow and Rifkin⁹ and by Zinneman.¹⁰ May¹¹ reported a 35-percent prevalence of hookworm infection in 400 U.S. soldiers interned for more than 3 years by the Japanese. Prevalence ranging from 20 to 48 percent was recorded in insular troops assigned to the Panama Canal Department and in Puerto Rican troops stationed in California. Infections in most cases were light, since routine stool examination and anthelmintic therapy had been given following induction. Had such examinations not been made, the infection rate and hookworm burden probably would have been much higher.¹²

Relation Between Eosinophilia and Hookworm Infection

The relationship between hookworm infection and eosinophilia was the subject of several investigations in the South Pacific. On the basis of these studies, it was concluded that, despite inaccuracies due to eosinophilia from other causes, eosinophilia could be used as an indirect criterion of the incidence of hookworm infection, when mass stool examination was impracticable.¹³ An eosinophilia of 6 percent or higher was taken as sufficient evidence of hookworm infection to justify treatment. Studies including two stool examinations made at the 39th General Hospital, Auckland, New Zealand,

⁹Zarrow, M., and Rifkin, H.: Intestinal Parasites Diagnosed at an Army General Hospital in the South Pacific. Am. J.M. Sc. 212: 289-293, September 1946.
¹⁰Zinneman, H. H.: Ankylostomiasis. Nebraska M.J. 32: 185-186, May 1947.
¹¹May, E. L.: Parasitologic Study of 400 Soldiers Interned by the Japanese. Am. J. Trop. Med. 27: 129-130, March 1947.
¹²(1) Professional History of Internal Medicine in World War II, 1 January 1940 to 1 October 1945, The Panama Canal Department, vol. II, pp. 251-254. [Official record.] (2) Report, G. H. Houck, P. L. Burlingame, M. S. M. Watts, and J. T. Marconis; 4th AA Command, 5 Aug. 1945, San Francisco, Calif., subject : Report of Disinfestation Program in 762d and 891st AA Gun Bns. (3) Letter, Lt. Col. J. L. Crary, Adjutant, 37th Antiaircraft Artillery Brigade, Coast Artillery Corps, to Commanding Officer, 891st and 762d Antiaircraft Artillery Gun Battalions, 29 June 1945, subject: Disinfestation of Personnel With Intestinal Parasites. (4) History of Medical Department Activities, Antilles Dept., Preventive Medicine, pp. 58-65. [Official record.]
¹³Stevens, Frank W.: [History, World War II] Medicine-South Pacific Area, pp. 24-25. [Official record.]

upon troops long in combat in the Solomon Islands, showed that 79 percent of those with an eosinophilia of 9 percent or above had hookworm ova in their stools. The blood studies indicated that at least 236 out of 1,000 in the command probably were infected with hookworm. In a smaller series of 50 selected soldiers studied at the 8th General Hospital, Dumbea Valley, New Caledonia, the range of eosinophilia was from 4 percent to 77 percent. Examination of three stools from each of these soldiers revealed hookworm infection in 98 percent of the group.

Brig. Gen. Earl Maxwell, Surgeon, USAFISPA (U.S. Army Forces in the South Pacific Area),¹⁴ directed that, in view of the apparent prevalence of hookworm in troops in South Pacific islands, it was important that all patients admitted to a hospital have a differential leukocyte count and at least one examination of the stool for parasites. In the presence of eosinophilia of 6 percent or above, presumptive evidence of hookworm was strong, and repeated examinations of the stool were indicated. It was the policy in this theater to investigate and treat hookworm disease in combat troops during periods of rehabilitation. However, surgeons responsible for the medical care of service troops and small combat organizations were urged to arrange eosinophilic surveys as soon as possible. Surgeons were directed to arrange for blood examinations to be made in permanent medical installations. In large numbers of troops thus surveyed, an eosinophilia of 6 percent or above was considered sufficient evidence of hookworm disease to justify treatment.

Psychoneurosis.-The differentiation of manifestations of hookworm infection and of psychoneurosis created a diagnostic problem in some areas. Denhoff¹⁵ reported that a large Army station hospital with 36 months` service in the South Pacific and Southwest Pacific had a substantial number of patients with high degrees of eosinophilia, the causes of which were not being determined by routine methods. During the period 1944 to 1945, while located in New Guinea, the medical and laboratory services established a ward for cases of unexplained eosinophilia in order to study hospital patients on whom laboratory studies did not clarify the cause of eosinophilia. Fifty-nine U.S. soldiers were studied in this group. Forty-seven (80 percent) were found to have intestinal helminths. Forty-two (71 percent) had hookworm infection. Five (8 percent) were infected with Strongyloides stercoralis. Twelve (20 percent) presented no demonstrable cause of the eosinophilia. The majority of patients were admitted to the hospital with abdominal complaints. A substantial number were classified as psychoneurotic prior to study. The predominant symptoms were intermittent cramplike epigastric pain, anorexia, nausea, vomiting, weakness, fatigue, nervousness, and weight loss. It was the opinion of Denhoff that the diagnosis of psychoneurosis may not have been warranted in troops with the syndrome described above.

¹⁴Medical Circular Letter No. 15, Office of the Surgeon, Headquarters, USAFISPA, 2 Feb. 1944, subject: Hookworm.
¹⁵Denhoff, E.: The Significance of Eosinophilia in Abdominal Complaints of American Soldiers. New England J. Med. 236: 201-206, February 1947.

The Problem of Ancylostoma duodenale

From the examples of studies and experiences with hookworm infection in U.S. Army troops stationed overseas, it is apparent that infections with A. duodenale were numerous. Although there is evidence that some of the infections were clinically significant, the majority of cases were asymptomatic and did not constitute a military problem of great magnitude. Provision of an adequate diet sufficient in iron probably helped to keep many hookworm infections at a subclinical level and to prevent the development of severe hookworm disease. According to Lt. Col. (later Col.) Francis R. Dieuaide, MC,¹⁶ it is unlikely that the health of military patients suffered in any significant degree from this infection. Hookworm infections are rarely serious for the individual who receives adequate treatment such as was given in the Armed Forces. As for the potential military significance of hookworm infection, Maj. (later Lt. Col.) Averill A. Liebow, MC, and Lt. Clair A. Hannum, SnC,¹⁷ speculated that subclinical hookworm infection might become hookworm disease if dietary intake of troops should become bad. Reexposure by repeatedly sending troops already infected in mass into new campaigns on contaminated soil might also reduce the efficiency of the military machine significantly.

Native populations in areas where sanitation was inadequate provided a reservoir of hookworm infection and constituted a hazard to troops stationed near their villages. Surveys conducted before World War II, recording the geographic distribution of hookworm infection in tropical Pacific islands, were summarized by Mumford and Mohr.¹⁸ During the war, medical laboratories, and particularly malaria survey units, conducted numerous surveys for intestinal parasites among natives in areas of troop concentrations. A survey of the 32d Malaria Survey Unit¹⁹ demonstrated a 91-percent prevalence of hookworm infection in a native labor camp at Nadzab, New Guinea. Of 282 fecal examinations from the civilian population adjacent to Tacloban airstrip in the Philippines, 74 percent were positive for hookworm ova.²⁰ Following the Makin and Kwajalein operations in 1944, a survey for intestinal parasites was conducted among the natives and prisoners of war. The series included 83 Japanese prisoners and 244 Korean laborers from the Gilbert and Marshall group. The prevalence of hookworm infection for the two groups was 26.5

¹⁶Dieuaide, F. R.: Wartime Experience With Tropical Diseases and Their Future Significance. Tr. A. Life Insur. M. Dir. America 30: 220-238, October 1946 (1947).
¹⁷See footnote 8 (1), p. 18.
¹⁸Mumford, E. P., and Mohr, J. L.: Manual on the Distribution of Communicable Diseases and Their Vectors in the Tropics, Pacific Islands Section, pt. I. Am. J. Trop. Med. 24: (Supp.) 1-26, May 1944.
¹⁹(1) Letter, Karl V. Krombein, Headquarters 32d Malaria Survey Unit, Unit I, to Commanding General, Far East Air Force, 25 June 1944, subject: Survey of Native Populations in the Nadzab Area for Intestinal Helminths, I. Native Laborers at the ANGAU Native Labor Camp, Nadzab. (2) Bern, H. A., and Hansen, M. F.: Parasitic Infections Among Natives of the North Markham Area. New Guinea J. Parasitol. 36: 103-106, April 1950.
²⁰Semimonthly Report of Activities of the 19th Medical Service Detachment (General Laboratory), 1-15 Mar. 1945.

and 34.4 percent, respectively.²¹ It is obvious that a potential source of hookworm infection for troops was present in many tropical areas.

The medical services stationed overseas and in the United States were kept informed of the frequency with which troops were acquiring hookworm infection. The common modes of exposure of troops were explained. Information and recommendations for the diagnosis, management, and prevention of hookworm infection were disseminated by various circular letters,²² articles published in the Bulletin of the U.S. Army Medical Department,²³ and technical manuals.²⁴ The following factors, instructions, and policies were relied upon to prevent and to minimize the severity of hookworm infection in troops: Wearing of shoes, intake of an adequate diet to compensate for blood loss and thus prevent or reduce clinical manifestations, avoidance insofar as possible of intimate contact with moist ground, avoidance of the use of native villages and abandoned or captured enemy bivouac areas as campsites, treatment of infected troops including mass treatment during periods of rehabilitation between combat engagements, and proper disposal of excrement even under combat conditions. During the war, consideration was given to research on control of hookworm infection through treatment of soil. Soil fumigants were considered impracticable for field use. Therefore, since other projects had higher priority and greater promise, no research along this line was undertaken.

Precautions against importation of A. duodenale into the United States.-The danger of implanting A. duodenale, the Old World hookworm, in the United States, where it was not endemic, was stressed by many persons including Wright,²⁵ Loughlin and Stoll,²⁶ and McCoy.²⁷ This matter was of public health importance in the United States. A. duodenale is more harmful to the host and less amenable to treatment, and its free-living stages are more resistant to climatic conditions than are those of N. americanus. It was estimated that 1 in 15 servicemen returning from the Pacific was infected with A. duodenale. Also, an analysis of hookworm infections in U.S. servicemen from the South suggested the persistence in young adulthood of faulty hygienic habits acquired in childhood. In returned servicemen, the occurrence of a significant incidence of A. duodenale infection, combined with evidence

²¹History of Internal Medicine in the Central Pacific in World War II, pp. 219-225. [Official record.]
²²(1) See footnote 14 (p. 20). (2) Circular Letter No. 33, Office of the Surgeon General, U.S. Army, 2 Feb. 1943, subject: Treatment and Control of Certain Tropical Diseases.
²³(1) Hookworm Infection in the Pacific Area. Bull. U.S. Army M. Dept. No. 78, pp. 3-4, July 1944. (2) The Management of Hookworm Infection. Bull. U.S. Army M. Dept. 4: 660-661, December 1945.
²⁴War Department Technical Manual 8-210, Guides to Therapy for Medical Officers, sec. VI, Treatment and Control of Certain Tropical Infections, par. 59, Hookworm Infections, 20 Mar. 1942.
²⁵Wright, W. H.: Present and Post-War Health Problems in Connection With Parasitic Diseases. Science 99: 207-213, March 1944.
²⁶Loughlin, E. H., and Stoll, N. R.: Hookworm Infections in American Servicemen With Reference to the Establishment of Ancylostoma Duodenale in the Southern United States. J.A.M.A. 136: 157-161, January 1948.
²⁷McCoy, O. R.: Precautions by the Army to Prevent the Introduction of Tropical Diseases. Am. J. Trop. Med. 26: 351-355, May 1946.

of continuance of practices favorable for dissemination of hookworm, increased the suspicion that this species of hookworm may have an opportunity to establish itself in endemic areas of N. americanus infection in the South.

McCoy pointed out that an attempt to remove every single hookworm from troops returning to the United States was not considered practicable because of the difficulties of examining and treating such a large group of men and because repeated treatment may be necessary to effect complete cure. However, it was realized that the possibility of establishment of A. duodenale in extensive areas in this country would be materially lessened if the number of worms introduced by returning troops was kept to a minimum. Consequently, survey and treatment of troops, especially those in combat units exposed to infection, were encouraged before departure from abroad. Also, McCoy recommended that individuals who had been treated for hookworm in the previous 6 months should be examined at time of discharge and given additional treatment if hookworm eggs were found. On 1 October 1945, a letter was addressed to the Commander in Chief, USAFPAC (U.S. Army Forces in the Pacific), by The Surgeon General, in which the following steps were suggested to minimize the possibility of introduction and establishment of A. duodenale infections in the United States from the Pacific: (1) Survey of representative samples (5 to 10 percent) of units to determine those in which an appreciable amount of hookworm infection had been acquired, (2) stool examination of all individuals in units in which the survey showed a prevalence of infection of more than 5 percent, and (3) treatment of all individuals found positive on stool examination. Col. Paul I. Robinson, MC, Deputy Chief Surgeon, USAFPAC, directed on 17 October 1945 that the hookworm detection and removal procedures suggested in the 1 October 1945 letter from The Surgeon General should be effected as far as practicable in troops departing for the United States.

SUMMARY

Between 1942 and 1945, there were 22,238 admissions for hookworm infection in the U.S. Army. The hookworm burden in most of the troops was light, but some of the infections were clinically significant. The majority of patients admitted for hookworm became infected overseas. Admission rates were 0.53 for soldiers in the continental United States and 1.35 for oversea forces. Many troops acquired infection with A. duodenale, the Old World hookworm, which was not endemic in the United States. Areas with the highest admission rates were the Southwest Pacific, Latin America, the Central and South Pacific, and China-Burma-India. No deaths in U.S. troops were attributed to hookworm disease. Admissions for hookworm may be considered relatively low. This interpretation seems justifiable in view of the large number of troops sent to the tropics, the nature of their military activities which frequently resulted in unavoidable exposure, and the prevalence of infection in

sometroops who had resided in endemic hookworm areas in the Southern United Statesand Latin America before military service.

Hookworm infection in theSouth Pacific appeared to be acquired largely during combat. Infantry troops andcombat medical troops acting as stretcher bearers had the highest infectionrates. Occupation of native villages and captured enemy bivouac areas resultedin increased infection. In combat, troops lived on the ground and often slept inwet foxholes. Under frontline combat conditions in the tropics, intimate contactwith moist soil was unavoidable. Some deficiency in proper excreta disposalwas reported.

Eosinophilia was used in onetheater as an indirect criterion of hookworm infection when mass stoolexamination was impracticable. An eosinophilia of 6 percent or higher was takenas sufficient evidence of hookworm infection to justify treatment. Thisprocedure, though expedient, would result in missing many other causes ofeosinophilia, particularly strongyloidiasis. In the South Pacific, combat troopswere surveyed and treated for hookworm infection during periods ofrehabilitation. The differentiation of manifestations of hookworm infection andof psychoneurosis created a diagnostic problem in some areas. The provision ofan adequate diet for Army troops probably contributed significantly to theprevention of severe hookworm disease. If the dietary conditions of troopsshould become inadequate, subclinical hookworm infection might reach the levelof hookworm disease.

It has been estimated that 1in 15 servicemen returning from the Pacific was infected with A. duodenale. ThePreventive Medicine Service, Office of the Surgeon General, was cognizant of thepossibility of introduction of this species of hookworm in the United States byrepatriated troops. Treatment of heavily infected oversea units prior to theirreturn was urged to minimize the possibility of establishment of A. duodenale inthe United States. No endemically acquired infections with this species in theUnited States were reported during the war years.

Important measures whichwere employed to minimize the medicomilitary significance of hookworm infectionwere as follows: Wearing of shoes, avoidance insofar as possible of intimatecontact with moist ground, avoidance of the use of native villages andcaptured enemy bivouac areas as campsites, proper disposal of excreta evenunder combat conditions, survey and treatment of infected troops duringrehabilitation periods between combat engagements, intake of an adequate diet toprevent or reduce clinical manifestations, and instruction of troops and ofline and medical officers in proper preventive and control measures.

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