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Chapter V




Harry Most, M.D.

Helminthic infections1 were acquired by a relatively large number of military personnel during World War II. The parasites discussed in this section may be classified as follows: (1) Those that enter the body as larvae via the skin or mucous membrane (hookworm and Strongyloides stercoralis) and (2) those that enter the body via the gastrointestinal tract (Ascaris lumbricoides, Trichuris trichiura, Trichinella spiralis, Enterobius vermicularis, and tapeworms).

Particularly in the Pacific islands, every possible condition existed to facilitate the dissemination of intestinal parasites. Infection in native and enemy troop populations was high, troops frequently operated in terrain containing human feces; facilities for fecal disposal were limited or nonexistent; and facilities for washing hands, bodies, clothing, and mess equipment were either limited or absent.

Table 21, compiled from data from seven surveys,2 shows the high incidence of parasitism in the various groups of natives and prisoners in areas where the U.S. Army operated under military conditions. The unsanitary living conditions made the acquisition of many of the parasitic infections almost inevitable.

Table 22, which represents the results of surveys done overseas and in the United States,3 shows the extent of infections in troops in the United States. The incidence was at least twice as great in troops who served in the Pacific as in those who served in the continental United States only; in general, probably, the incidence of infection overseas was actually greater than is indicated in the table. Examinations of single specimens of stool by direct smear only were frequent. Troops surveyed after returning to the United States may previously have had courses of treatment. Higher percentages were discovered in small groups who were not treated previously and in those in whom several stools were examined by concentration techniques.

1Schistosomiasis and filariasis which are discussed in chapters 3 and 4, respectively, are excluded from the discussion in this chapter.
2The various sources from which the data were compiled are listed in table 21.
3The various sources from which the data were compiled are listed in table 22.


TABLE 21.-Prevalence of parasitism in various groups of natives and prisoners, in tropical areas



The incidence of hookworm infections varied in different areas and frequently was related to the branch of service (being highest in the infantry) and to the duration of combat or to the length of residence in the area. A total of 800 cases were discovered among 2,000 Australian troops who had been in combat in New Guinea for periods of several weeks to months; 97 percent of one brigade was infected. In American troops serving in the Pacific, the prevalence was from 10 to 15 percent, according to several large surveys. After campaigns in the Solomon and Philippine Islands, as many as 20 to 40 percent infected might be found among those surveyed.


TABLE 22-Prevalence of parasitism in U.S. Army troops, oversea service and service in continental United States only

Area of service and of survey

Number of troops examined

Percent parasites recovered


Strongyloides stercoralis

Trichuris trichiura

Ascaris lumbricoides

Entamoeba histolytica

Schistosoma japonicum

(1) Solomon Islands








(2) South Pacific








(3) South Pacific








(4) Manila








(5) Leyte








(6) Leyte1








(6) Pacific1








(6) European and     Mediterranean1








(7) Pacific1








(7) European1








(7) United States2








(8) Pacific1








(8) United States2








1Area of service; the survey was conducted in the United States.
2Service in continental United States only.

NOTE.-Figures in parentheses identify source of data.
    (1) Essential Technical Medical Data, U.S. Army Forces, South Pacific Area, for February 1944, dated 7 Mar. 1944.
    (2) Essential Technical Medical Data, South Pacific Base Command, for March 1945, dated 15 Apr. 1945.
    (3) Essential Technical Medical Data, South Pacific Base Command, for April 1945, dated 15 May 1945.
    (4) Essential Technical Medical Data, U.S. Army Forces, Pacific, for October 1945.
    (5) Medical Bulletin No. 19, Office of the Surgeon, Headquarters, Army Service Command I, Okinawa, 17 Sept. 1945.
    (6) Hesselbrock, W. B., Lippincott, S. W., and Palmer, E. D.: Large-Scale Routine Examinations of Stool for Parasites; Practical Experience in a General Hospital in the Zone of Interior. Am. J. Clin. Path. 16: 264-269, April 1946.
    (7) Report, Fourth Service Command Laboratory, 3 Mar. 1946.
    (8) Most, 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.

Some infections disappeared spontaneously with the passage of time and many were eradicated by repeated courses of treatment, reducing the figure to about 10 percent by the time surveys were conducted in the United States.

Only about 5 percent of the troops who served in the European and Mediterranean theaters had hookworm. This was similar to the findings in men who served in the United States only, with the exception of one survey4 which was conducted at a separation center in the southern part of the United States, where the incidence of infection was notably higher (12.9 percent of those examined). Sanitary and combat conditions in the European and Mediterranean areas were often favorable to the acquisition of parasites. That infection did not occur more frequently may have been

4Report, Fourth Service Command Laboratory, 3 Mar. 1946.


due to low native and enemy troop infection in those areas, to particular combat conditions, or to insufficient time or temperatures for development of infecting larvae. Generally speaking, the infections discovered in men returning from the European and Mediterranean theaters were regarded as having been acquired in the United States before military service, although some may have been the result of local conditions overseas.

Hookworm infection in troops who saw no oversea duty was about 5 percent and was a reflection of the existence of hookworm in various southern States. A small number of infections due to Necator americanus may have been acquired during maneuvers in hookworm areas in the United States.

Nature and Severity of Infections

Few attempts were made overseas to recover adult hookworms after treatment, and few egg counts were done. At the 39th General Hospital, Auckland, New Zealand,5 stool egg counts in 39 patients varied from 350 to 71,000 per gram of feces, the majority being between 1,000 and 5,000. A total of 602 worms, all Ancylostoma duodenale, were recovered from 11 patients, 411 of the worms from the patient having the 71,000 stool count. The same parasite was recovered from 3 patients treated at the 8th General Hospital, Dumbea Valley, New Caledonia,6 and from 8 of 14 patients reported from India.7 The series from India included also two patients with Necator parasites and four with both varieties. The number of worms in the 14 cases in India varied from 8 to 100. These scattered figures indicate that Ancylostoma was responsible for a considerable number of mild infections.

Further studies in the United States have confirmed this impression. In one general hospital,8 out of 169 patients from whom adult worms were recovered after treatment, 87 had Ancylostoma, 69 had Necator, and 13 had both. The majority of hookworm infections acquired overseas were Ancylostoma, although a few men from northern nonhookworm areas picked up Necator (which is the variety endemic in southern United States), and some already infected with Necator acquired Ancylostoma as well.

On the whole, hookworm infections were not heavy. The number of worms recovered per patient in all but 14 of the 169 patients just mentioned was 25 or less. The maximum number of Necator was 86 and of Ancylostoma, 112. The average stool count for Necator infections was 1,900 (range 100 to 9,100) and for Ancylostoma, 2,295 (range 200 to 9,800). All

5Essential Technical Medical Data, U.S. Army Forces, South Pacific Area, for June 1944, dated 5 July 1944.
6Essential Technical Medical Data, South Pacific Base Command, for April 1945, dated 15 May 1945.
7Essential Technical Medical Data, U.S. Army Forces, India-Burma Theater, for June 1945, dated 1 Aug. 1945. Enclosure 4 thereto.
8Most, 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.


169 patients had had previous courses of treatment, but in another group not previously treated the average stool counts for Necator and Ancylostoma were 2,400 and 3,200, respectively. It is pertinent to recall here that A. duodenale lays almost twice as many eggs a day as N. americanus. Stool counts of the same order of magnitude have been reported in other series.

Whether Ancylostoma will become established in the United States, time will tell.9 Persisting infections will, presumably, be extremely light. An attempt was made to survey troops overseas and to treat the positives before they left. The pressure of demobilization, however, was so great that it was impossible to carry out this program.

Effect of Infection on the Host

As a rule, several hundred hookworms are necessary to produce symptoms. Since less than 25 worms were present in 90 percent of Army cases, it is not surprising that hookworm disease was a very uncommon manifestation of hookworm infection. Anemia was infrequent and usually mild, but leukocytosis and eosinophilia were common. Numerous courses of treatment were often required to eliminate all worms, resulting in prolonged hospitalization of patients. In occasional cases, clinical symptoms were disabling, and the basis for acute or chronic vague complaints was obscure until hookworm infection was discovered. These factors are discussed briefly.

Anemia.-Severe anemia did not occur in U.S. troops, and much of the mild anemia observed may have been due to tropical and military conditions rather than to hookworm infection. In one report,10 15 percent of 907 men without hookworm had erythrocyte counts below 4 million and 37 percent had a hemoglobin of less than 80 percent. Only 20 percent of 93 men with hookworm had erythrocyte counts below 4 million and 34 percent had hemoglobins less than 80 percent. The difference in the two groups is not significant. In one study11 of 74 patients with hookworm, 48 of whom had gastrointestinal symptoms, only 3 had anemia (hemoglobin 11 to 13 gm.). In another series,123 of 39 patients had anemia (red blood cells 2.9 to 3.8 million, hemoglobin 56 to 76 percent). In a general hospital in the United States, among 100 men who had hookworm as an incidental finding,13 there was none with anemia attributed to this infection.

White blood cells.-Leukocytosis and eosinophilia commonly occurred early in the course of hookworm infection. The persistence of the latter for many months was used in estimating the probable rate of hookworm infec-

9Up to 1953, no case of this parasite acquired in the United States has been reported.
10Essential Technical Medical Data, U.S. Army Forces, South Pacific Area, dated 1 Feb. 1944.
11Hodes, P. J., and Keefer, G. P.: Hookworm Disease; A Small Intestinal Study. Am. J. Roentgenol. 54: 728-742, December 1945.
12See footnote 5, p. 148.
13See footnote 8, p. 148.


tion in the 43d Infantry Division.14 When compared to positive stool counts, however, eosinophilia did not prove to be a very reliable criterion. Examination of one or two stools by brine flotation in judiciously sampled, representative small groups is a more satisfactory method. Eosinophilia occurred most frequently in infantry combat outfits and was directly related to the duration of combat or to the length of residence in the endemic area. The peak occurred 3 or 4 months after the greatest exposure and fell in a little over 8 weeks' observation. The highest eosinophilia observed was 68 percent and the greatest leukocytosis, 28,000. Eosinophilia, ranging from 10 to 70 percent, was found in other groups of patients with hookworm in India.15 An average eosinophilia of 10.2 percent in a group of 100 men in the United States,16 with hookworm as the only parasitic infection, attests to the persistence of this sign.

Clinical findings.-Hookworm disease was evident in only 5 of a series of 600 patients with hookworm infection.17 However, various clinical signs and symptoms were observed that were attributed to the infection. In India, abdominal pain and tenderness, nausea, vomiting and diarrhea, and eosinophilia in some patients were not explained until hookworm eggs were found in the stools. In 50 selected cases of apparently recent hookworm infection,18 the onset of symptoms was often acute, simulating gastroenteritis. The signs and symptoms noted in this group are as follows:

Signs and symptoms:



Diffuse abdominal pain, after meals and during the night



"Foxhole" cough without coryza or sore throat, appearing 1 to 2 weeks after ground itch and lasting 3 weeks



Abdominal tenderness



Diarrhea (average 6 stools per 24 hours) without blood or pus



Ground itch 4 to 6 weeks before onset of abdominal symptoms



Anorexia and weight loss


Low grade fever


The leukocytes numbered as many as 41,000 per milliliter, averaging 13,700 per milliliter. The maximum percentage of eosinophiles was 70 percent, averaging 34 percent. Eggs were found in a single direct smear examination of the stools in 21 percent and in 57 percent after repeated examinations. When concentration methods were used, 86 percent of first examinations were positive, and all were positive with three examinations. From 8 to 100 adult worms per patient were collected from 14 cases.

Treatment completely relieved 20 percent of the 50 patients of symptoms, improved 55 percent, and produced no change in 25 percent. Stools were positive after two courses of treatment in 63 percent of the men.

14Liebow, A. A., and Hannum, C. A.: Eosinophilia, Ancylostomiasis, and Strongyloidosis in the South Pacific Area. Yale J. Biol. & Med. 18: 381-403, May 1946.
15See footnotes 7, p. 148; 10, p. 149; and 11, p. 149.
16See footnote 8, p. 148.
17See footnote 14.
18See footnote 7, p. 148.


Complete gastrointestinal studies were conducted in a general hospital in Burma19  on 74 patients whose symptoms appeared several weeks after their arrival in that country. Of the 74 patients, 48 were hospitalized because of abdominal symptoms and the rest, for other reasons. The majority of the 48 patients complained of dull, cramping, or gnawing intermittent abdominal pain, most marked in the epigastrium or the midabdomen. In some patients, the onset was acute, marked by nausea, vomiting, pain and diarrhea, and occasionally fever with a temperature of about 100? F. Anorexia and bloating were common. The clinical diagnosis at onset was frequently peptic ulcer. Change from field rations to bland hospital diet brought no relief. In 54 acute cases, eosinophilia was between 10 and 70 percent, half being over 30 percent. The erythrocyte count and hemoglobin values were normal in all but three patients.

Roentgenographic studies.-Roentgenographically, the intestines of the 54 patients showed the following:

Distal duodenum.-No disturbance in tone or rugal pattern in mild infections. Moderate to marked thickening and prominence of mucous membrane in 26 patients. Irritability. Tenderness on palpation frequent.

Jejunum.-Tenderness on palpation in most cases. Rugal abnormalities, from slight prominence of the valvulae conniventes to severe coarsening of the mucosal folds in 60 percent of patients. Serrations between folds and height and contour of rugae variable. Normal intestinal tone in half the patients; increased tone in half, with narrowing of lumen and shortening of loops. Irritability.

Ileum.-Rugal prominence in contour similar to ileum but to a lesser degree. Normal mobility in majority; delayed mobility in 30 percent. Normal tone in half the patients; increased tone in half, producing bolus formation and segmentation.

These changes, which are those of a disordered motor function, appeared first in the proximal jejunum, then in the distal duodenum and distal jejunum, and finally in the entire ileum in severe cases. It was suggested that they resulted from disturbance in the intramural nervous mechanism of the myenteric and submucosal plexuses. Edema and cellular changes in the wall of the intestine associated with the presence of adult hookworms were of secondary importance. In a fatal case of scrub typhus, 260 Ancylostoma were found in the small intestine. Small erosions of the mucosa, edema, ecchymosis, and occasional worms in the submucosa were observed. After one or more courses of treatment, improvement was manifested by loss of tenderness to palpation, loss of hypermotility and irritability, and restoration of normal tone. Recovery was complete in mild cases within a few weeks after treatment, but X-ray changes sometimes persisted for months.

19See footnote 11, p. 149.



It was a disappointment to find that tetrachloroethylene was frequently unsuccessful in eliminating all hookworms. In one oversea hospital,20 only 46 percent were cured after a course of 4.0 ml. tetrachloroethylene, 74 percent after three courses, and one patient required seven courses before stools became negative. In a series of 50 in India,21 63 percent of the men had positive stools after two courses, while in another oversea area22 only 50 percent of 600 men were reported free of infection after 1 to 14 courses.

The unexpected failure of tetrachloroethylene was shown23 to be due to the relative refractoriness of Ancylostoma to the drug as compared to Necator. Stools were examined from patients with untreated hookworm before, and a week after, treatment, and the results correlated with the species of adult recovered. Only 25 percent of 35 patients with proved Ancylostoma infections were cured after one course of 4.0 ml. tetrachloroethylene, and 55 percent after two courses. This contrasts with 66 percent of 24 patients with Necator cured after one course of treatment and 85 percent after two courses. Since Ancylostoma accounted for three-fourths of hookworm acquired overseas, the resistance of this species explains the poor results obtained. Drug deterioration in the Tropics was not responsible since use of fresh drugs in the United States gave no better results. Of 100 men previously treated overseas, 42 percent were cured by one course of treatment in the United States, 79 percent were cured after three treatments, and 98 percent after six treatments. It is probable that Necator infections were largely eliminated by prior treatment and failures were due to the persistence of Ancylostoma. Increase of dosage of tetrachloroethylene to 5.0 ml. did not improve its efficacy.

No striking toxicity was observed after from 3.0 to 5.0 ml. doses in thousands of men. A combination of tetrachloroethylene and oil of chenopodium was not thoroughly tested. Hexylresorcinol apparently was relatively ineffective in eliminating hookworm infections, but no detailed studies were conducted.

Military Aspects of Hookworm Infections

Since the vast majority of hookworm infections were light, producing no anemia or symptoms, the military efficiency of U.S. troops was not impaired by such infections. Severe infections resulted in hospitalization of a small number of men, but for the most part hookworm infections were discovered incidentally in the course of surveys or hospitalization for other causes.

20See footnote 5, p. 148.
21See footnote 7, p. 148.
22See footnote 14, p. 150.
23See footnote 8, p. 148.


Failure of treatment often resulted in needlessly prolonged hospitalization of men who were clinically well but still had hookworm eggs in the stools or prolonged eosinophilia. At Fort Bragg, N.C., for example, 61 patients, in whom hookworm was discovered incidentally, lost an average of 14.4 days per man (longest 48 days) because of repeated courses of treatment.24 It was recommended from that station that 2 days on quarters' status was sufficient for treatment. A similar recommendation to minimize time lost from duty was made by an antiaircraft medical officer.25 Because most infections were subclinical and because Ancylostoma was often not eliminated by tetrachloroethylene, it was officially recommended in 194526 that treatment be limited to two courses.



Infections due to Ascaris lumbricoides did not constitute a clinical or military problem. Ascariasis was discovered in relatively few troops (1 to 3 percent) after their return from overseas. This is probably due to the short lifespan of this parasite and to the fact that hexylresorcinol, which is fairly effective against Ascaris, was frequently used in treating hookworm infections. However, Ascaris infection was rather prevalent in certain Pacific areas in which the local incidence was very high. It was found in 18 percent of 630 American troops in the vicinity of Manila and in 34.4 percent of 206 men in an engineer group on Leyte. Infections were not symptomatic and were easily eliminated with hexylresorcinol.27 Prolonged hospitalization was rare.


The incidence of strongyloidiasis in troops from the Pacific was from 1 to 3 percent. Strongyloides stercoralis were often found in patients who had hookworm. In 633 stools that were positive for hookworm or Strongyloides or both, 7.4 percent had Strongyloides.28 No reports of significant clinical symptoms caused by S. stercoralis are available, although severe diarrhea has been observed. Eosinophilia was common. No cases of chronic

24Williams, A. F., and Kinsman, J. M.: Management of Subclinical Hookworm Infestation in the Army. [Professional paper.]
25Report, G. H. Houck, P. L. Burlingame, M. S. M. Watts, and J. I. Marcones, 4th AA Command, San Francisco, Calif., 5 Aug. 1945, subject: Report of Disinfestation Program in 762d and 891st AAA Gun Battalions.
26The Management of Hookworm Infection. Bull. U.S. Army M. Dept. 4: 660-661, December 1945.
27Studies subsequent to the close of hostilities have shown the therapeutic value of piperazine hexahydrate (Antepar) in ascariasis. With daily administration of 50 to 75 mg. per kilogram for 5 days, the cure rate has been well above that observed following a single course of hexylresorcinol. Piperazine is also the drug of choice in treating pinworm infections.
28See footnote 14, p. 150.


infection or of pulmonary involvement have been reported. Discovery of this parasite in the stools or in material drained from the duodenum occasionally accounted for the existence of prolonged eosinophilia. Frequent failure of standard treatment with gentian violet medicinal (96 tablets, 0.03 gm. during 16 days) led to prolonged hospitalization. Intensive treatment via duodenal tube or gradual increase in daily dosage to the maximum tolerance (18 tablets daily) produced cures in one hospital. Differential diagnosis of strongyloidiasis and schistosomiasis japonica could often be facilitated by examination of liquid postcathartic stools or duodenal fluid.29


The incidence of trichuriasis in men from the Pacific was from 10 to 15 percent and closely paralleled the incidence of hookworm. Trichuris trichiura produced no symptoms or signs other than slight eosinophilia. One case of epileptiform convulsions, probably due to sensitivity to the protein of the adult worm, was observed by the author. Large amounts of anticonvulsant drugs were required for control, but after the elimination of worms with two courses of leche de higuer?n, convulsions ceased and did not return when anticonvulsants were omitted. Examination of stools for T. trichiura frequently led to discovery of other potentially more severe infections (Entamoeba histolytica). Common anthelmintics were not effective in eliminating whipworms, but, since these parasites were of no clinical significance, treatment was not attempted and hence prolongation of hospitalization did not ensue.

Creeping Eruption

A total of 19 cases of cutaneous infection with Ancylostoma braziliense larvae were reported from Camp Rucker, Ala., over a period of 2? years.30 The average time lost from duty was 27 days; the maximum, 77 days. Local freezing with ethyl chloride spray controlled the infection. Associated eosinophilia and pulmonary infiltration have been reported. The infrequency of this infection is somewhat surprising in view of the probability of exposure to terrain soiled by cat and dog feces.


For the years for which this information is available, a total of 14 cases of infections due to larvae of Taenia solium (cysticercosis) or Echino-

29Baroody, B. J., and Most, H.: The Relative Efficiency of Water Centrifugal Sedimentation and Other Methods of Stool Examination for Diagnosis of Schistosomiasis Japonica. J. Lab. & Clin. Med. 31: 815-823, July 1946.
30Annual Report, Camp Rucker, Ala., for 1944, dated 13 Jan. 1945.


coccus granulosus (hydatid disease) were reported in military personnel.31 

A small number of cases of dwarf tapeworm infections (Hymenolepis nana) were discovered incidentally to routine stool examination. Their origin may or may not have antedated military service. There were no clinical manifestations, and the infection was readily eliminated by several courses of oleoresin of aspidium. Dwarf tapeworms were present in some men who were on prolonged quinacrine suppression. This drug has been said to inhibit the development of a related parasite (Hymenolepis fraterna) in the mouse. Beef tapeworms (Taenia saginata) were very rarely found, possibly because of the use of federally inspected meat and, overseas, of large amounts of processed beef.


During World War II, a total of 285 admissions for trichinosis were reported in the U.S. Army. Of this total, 77 occurred outside the continental United States, giving an average rate of 0.01 per 1,000 average strength per year; the 208 admissions reported in the continental United States produced the same rate.

In May 1941, before the United States had entered World War II, a small outbreak of trichinosis occurred at Camp Edwards, Mass.,32 resulting in the hospitalization of 13 acutely ill soldiers. Diagnosis was proved in four cases by muscle biopsy. These patients were hospitalized for from 31 to 33 days. Skin tests were positive in 28 percent of the other 129 members of the same company who ate in the same mess. Thirty percent of these men also had eosinophilia above 10 percent, indicating that subclinical trichinosis may have been present in 25 percent of the company.


Parasitic infections occurred fairly extensively in World War II. This was principally due to operations in the Pacific islands where, with a high incidence among natives and enemy troops, living conditions and type of military operations presented a perfect background for infection.

Hookworm was the most common of the pathogenic helminths. In U.S. troops returning from the Pacific, the incidence of hookworm was at least twice that found in men who had served only in the United States or in Europe. Ancylostoma duodenale was responsible for the majority of infections. Infection was generally light, and hookworm disease was rare.

31According to sample tabulations of individual medical records, there were 13 admissions for echinococcus infection during 1942-45 reported among U.S. Army personnel, and 1 admission for cysticercosis in 1944 (none in 1945; data not available for 1942-43). Data on secondary cases, available only for the years 1944 and 1945, showed no cases for these diseases during the 2 years. All but one of the echinococcosis cases were admitted in the Zone of Interior; one in Hawaii. The cysticercosis case was admitted in the Mediterranean theater.
32Marble, A., Skoog, A. P., and Bucholz, D. J.: Trichinosis: Report of an Outbreak at Camp Edwards, Massachusetts. Mil. Surgeon 90: 636-643, 1942.


Tetrachloroethylene was not very effective in treating hookworm, particularly A. duodenale. Prolonged hospitalization of men without clinical symptoms, because of persistence of eggs in the stools, resulted in many days lost from duty. Military efficiency of U.S. troops was not impaired, but it is conceivable that a prolonged war in severely infected areas might result in heavy Ancylostoma infections of a more serious type.

Other common intestinal parasites were also prevalent, but these did not constitute an important medical or military problem.

Clothing and skin protection against larvae of hookworm or of Strongyloides, possible soil treatment for destruction of larvae or eggs, and development of more effective drugs for the treatment of Ancylostoma, Trichuris, and Strongyloides, remain to be achieved.