The American Journal of Tropical Medicine and Hygiene - Volume 23, Issue 5, September 1974

For many years members of our Society and scores of others here and abroad, with generous financial aid from many sources, have pursued research and published the results in miniscule detail. Many also have worked abroad in various public health and medical programs. The ultimate goal was to unravel Nature's secrets and benefit mankind, especially in the less developed parts of the world. The “rich” U.S. Government, 400 billion in debt, scores of foundations, solvent World Health Organization, industry, and the Church have participated in these activities. It is of these matters that I will speak after some 47 years of observing and participating in them. I shall give names of persons and countries only in connection with successes.

At the age of 24 I was the minor member, the Benjamin, of a hookworm research group, Rockefeller-supported, on the way to Nicaragua.

Mice infected with Plasmodium berghei yoelii responded poorly to pertussis vaccine when administered at peak parasitemia. This was shown by serum agglutinin titers and lack of protection against intracerebral challenge with virulent Bordetella pertussis.

Free-living amebas of the genus Naegleria, of world-wide distribution and long considered harmless, have been linked etiologically with 57 fatal cases of primary amebic meningoencephalitis during the last decade. Naegleria from cultures derived from one of these fatal cases in Richmond, Virginia, have been inoculated intranasally, intraorally, into the conjunctival sac near the inner canthus of the eyes, and into induced skin lesions in adult germfree guinea pigs. Of 33 animals inoculated intranasally with 18 to 31 amebas, 31 developed a fatal encephalitis. There was considerable destruction of tissues of the cerebellum and the cerebrum and including the olfactory lobes. The meninges were involved to varying degrees in most of the animals. None of the animals inoculated by the three other routes developed either symptoms or lesions.

During a 10-year period a series of 114 patients was studied to determine if Trypanosoma cruzi and arboviruses could be the etiologic agents of idiopathic cardiomyopathy (ICM) in Cali, Colombia. In this area, ICM (together with rheumatic and atherosclerotic cardiopathy) represents the second most frequent cause (determined by necropsy) among adult patients with cardiopathies, hypertension being the first. No association was observed between ICM and any of the arboviruses assessed by hemagglutination tests. Only 10 of 114 cases (8.7%) showed positive seroparasitological tests for T. cruzi. Autopsy was performed in 4 of these 10 cases; 1 had Chagas myocarditis and the other 3 were patients with noninflammatory ICM. In all 9 T. cruzi-negative cases the autopsies showed non-inflammatory ICM lesions. In contrast to typical Chagas cases, the most frequent EKG change in ICM is left bundle branch block rather than right. Since the EKG varies within either group, this distinction may not be valid in individual cases. Because of the similarities in clinical characteristics and variations in EKG between Chagas myocarditis and ICM, it is suggested that autopsies should be done in populations in endemic areas of T. cruzi to assess the frequency of ICM and its importance in the differential diagnosis of Chagas myocarditis.

A total of 3,523 wild caught monkeys from Panama was examined for blood parasites from August 1968 through June 1972. Trypanosomes or microfilariae were observed in the blood of 31.1% of the monkeys. Mixed infections, with microfilariae and trypanosomes, were detected in 6.6% of the animals. Trypanosoma cruzi was found in marmosets, Saguinus geoffroyi (12.2%), in white-faced capuchins, Cebus capucinus (5.0%), in squirrel monkeys, Saimiri sciureus (1.7%), and in black spider monkeys, Ateles fusciceps (1.2%). Trypanosoma rangeli was found in S. geoffroyi (55.8%) and C. capucinus (12.5%). Other trypanosomes found in Panamanian monkeys included T. minasense, and T. mycetae. Saguinus geoffroyi showed the highest infection rate (88.9%) with trypanosomes and/or microfilariae; trypanosomes were seen in 68.1%, and microfilariae in 73.0%, of the animals examined. The marmosets, white-faced capuchins, and squirrel monkeys should be considered as significant hosts of T. cruzi in sylvatic habitats and may serve as reservoir hosts of Chagas' disease in Panama. The microfilariae seen in monkeys from Panama were tentatively identified as larval forms of Dipetalonema gracile in Aotus trivirgalus; D. obtusa in C. capucinus and S. geoffroyi; and D. marmosetae in Alouatta villosa, C. capucinus, A. trivirgatus, S. sciureus, A. fusciceps, and S. geoffroyi.

In the reported cases of an infarct-like density caused by a filarial worm in a pulmonary artery the species involved usually was identified as a Dirofilaria. In most instances the worm was presumed to be D. immitis and was dead when discovered. In a recent such case the worm was identified as a sexually mature, infertile female Brugia, probably B. malayi, in a normal artery situated some distance from the lesion, and it apparently was alive when removed in resected lung tissue.

In the present case the findings were similar in that the worm was a living, sexually mature, infertile female lying free in a normal artery some distance from an infarct-like pulmonary density, but the morphological features evident in histopathological sections of the worm resembled those seen in Wuchereria bancrofti.

A survey carried out in Tonga, an area of hyperendemic subperiodic Wuchereria bancrofti filariasis, compared the diagnostic efficiency of the membrane-filtration and stained blood film techniques. Membrane filter concentration of 1 ml blood revealed a microfilaria rate that was approximately the same for all age groups, from 5 to 9 years old to > 50 years old, about 70%. The microfilaria rate by examination of stained 60 mm3 thick blood films was lower for all age groups. Membrane filter concentration detected 7.8 times as many infections as thick film diagnosis in the 5- to 9-year-old group, 4.8 times in the 10- to 14-year-old group, 2.4 times in the 15- to 20- and 21- to 50-year-old groups, and 1.6 times in the >50-year-old group. Concentration revealed the presence of microfilariae in the blood of 5 of 8 patients with gross elephantiasis, whereas microfilariae were found in the stained thick-film of only 1 of these individuals.

The in vitro diffusion of the organophosphate famphur from polydimethylsiloxane (PDS) capsules into plasma and their effects on Litomosoides carinii and Dipetalonema witei in jirds was studied. The in vitro rate of diffusion per 24 hours was constant and was directly proportional to the capsule lumen surface area and inversely proportional to the capsule wall thickness. One capsule implanted subcutaneously into each jird almost completely eliminated the microfilaremia of L. carinii while in situ (5 weeks) but had no effect on the levels of microfilaremia of D. witei. The adults of both species were unaffected. The capsules were well tolerated by the jirds and little tissue response to them was noted. The possibilities of using PDS-incapsulated drugs for prophylactic chemotherapy of canine and human filariasis is discussed.

Groups of 6 to 8 grivet monkeys (Cercopithecus aethiops aethiops), each of which had been exposed to 600 cercariae of Schistosoma mansoni, were killed 3, 6, and 31 months after exposure. Other groups of monkeys were repeatedly challenged with cercariae beginning 4 or 23 months after the initial infection, and were killed 31 months after the first exposure. Peripheral blood leukocytes, eosinophiles, and schistosome eggs passed in the feces were determined during the course of the infection. At autopsy, gross and histopathologic observations were made, worms were recovered by perfusion, and the number of eggs in the tissues was determined by digestion. Monkeys became acutely ill about 8 weeks after the initial exposure, and death was attributed to acute “toxemic” schistosomiasis in 4 of 46 infected animals. The symptoms and signs of the acute phase did not recur with reinfection. Most subsequent natural deaths were caused by Klebsiella infection, which occurred in both infected and control monkeys and did not appear to be related to the schistosome infection. Relatively stable infections were found after a single exposure to cercariae, with only a slight decrease in worm numbers and moderate decrease in egg passage after 31 months. With repeated reinfection, only 19% of challenge cercariae developed into adult worms. Oviposition by these worms was delayed and the rate of oviposition was substantially less than in monkeys infected only once. Eggs deposited in the tissues were rapidly destroyed. The calculated rate of oviposition varied from 658 eggs/day per female 3 months after a single infection to 299 eggs/day per female 31 months after repeated infections. Although very heavy infections were present in repeatedly infected monkeys, only slight hepatic fibrosis was seen and no portal hypertension or portal-systemic collateral circulation developed. Severe intestinal disease was present in only two monkeys. The remaining animals had little diarrhea after the acute phase, and there was only slight loss of plasma protein into the feces 31 months after exposure.

The course of a self-induced infection with about 100 Ancylostoma duodenale larvae was followed by twice-weekly blood and stool examinations. After a small initial increase, no further change in eosinophil counts occurred until the 33rd week of infection when they began to increase sharply. Seven weeks later, eggs were first observed in stools. Thus, in this infection, the prepatent period was five times the expected. It is suggested that a strain of A. duodenale exists which either 1) has an inherent, abnormally long prepatent period or 2) has a prepatent period which is susceptible to change depending upon the environmental conditions experienced by the free-living larvae. In either case, the third stage larvae probably enter a hypobiotic state within the host which lasts for about 8 months.

A 63-year-old, white, animal caretaker suffered intermittent abdominal pain and diarrhea of 3 weeks duration. Hematological findings included leukocytosis (18,600) with eosinophilia (73%). Fecal examination revealed Strongyloides rhabditiform larvae which on culture yielded a preponderance of filariform larvae and a few free-living adults. Thiabendazole therapy resulted in rapid recovery. Epidemiological investigation yielded no history of previous Strongyloides infection or exposure; his wife and pet dog were not infected, but about one-third of the dogs in the colony under his care were found to be discharging Strongyloides rhabditiform larvae in their feces. Strongyloides infection was successfully transmitted to specific pathogen-free pups using filariform larvae derived both from the human case and from the dog colony. Specimens recovered from one pup infected with filariform larvae of human origin were identified as Strongyloides stercoralis.

Investigations of schistosomiasis mansoni in 218 Yemeni agricultural workers in the San Joaquin Valley of California revealed a prevalence of 56%. In those infected, quantitative egg counts performed by the Kato thick smear method revealed that 57% had light infections (1–100 eggs/g), 27% moderate infections (101–400 eggs/g), and 16% heavy infections (>400 eggs/g; mean—918 eggs/g). The Yemeni had been migrating to the USA for the past 20 years, a period in which the prevalence of schistosomiasis had remained constant in the Yemen. The prevalence of schistosomiasis in those who had been away from Yemen for less than 5 years (up to 20 years) it was 32% with a mean egg output of 75 eggs/g. This is in spite of the fact that 75% of the latter had returned to Yemen for short visits. Statistical analysis by the Fisher's exact probability test revealed a significantly lower egg output in those away from Yemen more than 5 years. On the basis of these findings the mean life span of the Yemeni strain of Schistosoma mansoni in man was estimated to be between 5 and 10 years. The presence of disease was assessed in this population by traditional medical means without prior knowledge of the status of the infection in the individuals examined. Under these circumstances, there were no differences in symptoms such as weakness, diarrhea and abdominal pain among the uninfected proportion of the population, total infected group and a small subgroup of those most heavily infected. None of the patients had hepatomegaly and only two had splenomegaly—one lightly and the other heavily infected. Because of the toxicity of antischistosomal drugs and the lack of treatment facilities only the 22 most heavily infected (>200 eggs/g) of the 122 individuals with schistosomiasis mansoni were treated with niridazole. In addition, the two individuals with splenomegaly were treated with antimony dimercaptosuccinate. Side effects, though common, were not severe. Although follow-up in this migrant population was poor, the nine patients examined 3 to 7 months after treatment showed a mean decrease in egg output of 97%.

Of 433 schistosomiasis mansoni patients in St. Lucia who were treated with hycanthone (3 mg/kg of body weight), 190 were seen 2 years after treatment and 143 of these had attended all follow-up examinations at 6 weeks, 6 months, 1 year, and 2 years. Viable eggs were not detected in 86% at 1 year nor in 76% at 2 years. The reinfection rate, as judged by a significant increase in egg excretion, was 15% and was related to the geographic area to which the patient returned. Extremely high total reduction in egg excretion (98%) was achieved through 1 year, and even with reinfections this fell only to 87% at 2 years. Liver and spleen enlargement was related to intensity of infection and responded to treatment in 92% and 83% of instances, respectively. Among patients with hepatosplenomegaly, those 15 years or older showed less clinical response than younger patients but were too few for statistical comparison.

Plasmodium berghei yoelii infection in mice suppressed granuloma formation around Schistosoma mansoni eggs in the lungs. This suppressive effect was observed as early as 4 days after schistosome eggs were injected into malaria-infected mice and the maximum suppressive effect was seen by the 16th day. At that time granulomas in control mice were 58% larger than those observed in marlaria-infected mice. In addition, granuloma formation was found more consistently in control mice than in mice infected with malaria. These data suggest that malaria has a direct influence on an immunologic reaction of the delayed hypersensitivity type. There was no significant difference in the level of antibodies, specific for schistosome eggs, in the sera of the malaria-infected mice as compared to mice injected with S. mansoni eggs alone.

In Zaire, we studied 180 patients with Mycobacterium ulcerans infections and found 14 with a history of antecedent trauma at the site of the lesion (e.g., gunshot and land mine injuries, penetrating wood splinters, and scorpion stings). Two patients developed lesions following hypodermic injections. We believe that trauma is an important mode of transmitting M. ulcerans infections, or of introducing the etiologic agent into the dermis or subcutaneous tissue from superficially contaminated skin.

Eight patients from Zaire with Mycobacterium ulcerans infections were treated by the local application of heat to maintain a temperature of approximately 40°C in the ulcerated area. All lesions healed without surgical intervention and without local recurrences during follow-up periods of up to 22 months. This study shows that local heat promotes healing of M. ulcerans lesions. We postulate that the mechanism is primarily by direct inhibition of multiplication of M. ulcerans. Other possible contributory effects are discussed.

A skin infection survey of 1,084 people was carried out in two jungle villages in eastern Panama. Bacterial pyoderma was the most prevalent infection, affecting 25% of boys, 15% of girls, and 11% of those over 10 years of age. Streptococcus pyogenes and Staphylococcus aureus were recovered from 84% of pyodermas cultured. Nearly 60% of the cutaneous staphylococcal isolates were resistant to penicillin. Hippleates flies were seen feeding on purulent skin lesions and may have been important in transmission. Scabies, ringworm, candidiasis, and cutaneous leishmaniasis were rare in comparison with pyoderma, involving less than 1% of the population each. All of the ringworm infections were caused by Trichophyton rubrum.