The American Journal of Tropical Medicine and Hygiene - Volume 31, Issue 3, 1982

First I wish to thank Bob Shope for his kind introduction and all members of the Society for the privilege of serving as President and for the opportunity to address you.

In choosing a topic for this address, I, like my predecessors, was faced with two possibilities—one to discuss a specific scientific field related to my own research career and interests or instead, to consider a broader topic of interest to members of the Society.

In effect, the decision was made for me by the Charles Franklin Craig Lecture Committee and by the Craig lecturer of this year, Roy Chamberlain. First the Committee picked Roy and then Roy picked his topic—“Arboviruses—Then and Now.” This sequence of events in effect selected my topic.

As you all know, there is a common saying that if one dose of medicine is good, two are better; but we know that that assumption is usually false.

First of all, I want to thank the Charles Franklin Craig lecture Committee for inviting me here today. It's a great honor and one I shall always remember. Thanks also to all of you for showing up to hear me. And special thanks to my good friend, Dr. Thomas P. Monath, for his glowing, morale-raising introduction.

In the next 30 minutes or so I intend to give you a cursory view of arbovirology over the last 80 years, indicating the high points along the way which I feel have most strongly affected developments in this field. It will be biased, of course, in favor of mosquito-borne viruses, because that's all I know, and in favor of the Western Hemisphere, because that's where I'm from, but I hope I can be forgiven for that. Then in the wind-up, I'll present a number of basic concepts which attempt to explain, at least in part, why arboviruses behave the way they do and how they manage to survive.

Responses of parasitemia and fever in vivax malaria to standard doses of chloroquine and different dosage schedules of co-trimoxazole were compared in 165 children. Though both the drugs were effective, chloroquine was significantly faster in clearing parasitemia than all the dosage schedules of co-trimoxazole. No statistically significant difference was observed in rapidity of defervescence between chloroquine and the two high daily dosage regimens of co-trimoxazole. Gastrointestinal intolerance was persistantly higher with chloroquine. Asymptomatic sulphonamide crystalluria was seen in a large number of cases receiving the two high daily dosage schedules of co-trimoxazole.

Studies were initiated to determine whether or not transformation of lymphocytes isolated from individuals functionally immune to malaria would be a useful tool for the identification of protective antigens derived from continuous cultures of Plasmodium falciparum. Soluble antigen preparations stimulated lymphoproliferative responses in cells isolated from immune and nonimmune individuals. To rule out the possibility that those nonspecific responses were mixed lymphocyte reactions or other, undefined stimuli due to the heterologous nature of the lymphocyte culture system, subsequent experiments were conducted using extracts from parasites cultured in erythrocytes obtained from the same donors whose lymphocytes were tested. Soluble parasite extracts from continuously cultured P. falciparum produce nonspecific lymphocyte blast transformation responses in immunologically naive individuals. Such mitogens should be identified and removed from antigen preparations before a vaccine against malaria can be developed.

A case of congenital Chagas' disease in which intracranial calcifications were observed on examination at the age of 5 months is described.

Antibody levels to Trypanosoma cruzi were compared in asymptomatic individuals infected with the parasite as well as those with different forms of chronic Chagas' disease of varying severity. The following three serologic tests were used: complement fixation, direct agglutination with previous treatment of the serum with 2-mercaptoethanol, and the enzymelinked immunosorbent assay. The clinical groups tested included individuals with (a) a positive serology but no symptoms and without evidence of chronic disease (indeterminate form); (b) mega disease (groups I, II, III, and IV); (c) cardiomyopathy (mild, moderate, and severe); and (d) those with both mega disease and cardiomyopathy (combined form). The mean enzyme-linked immunosorbent assay and complement fixation antibody levels among the various clinical groups showed no statistical differences. With the direct agglutination test patients with mega disease and those with severe cardiomyopathy had slightly higher mean titers than patients in the indeterminate group and those with mild or moderate cardiomyopathy. While there may be possible reasons for these differences, the biological relevance of the findings was concluded to be of dubious significance.

Standard courses of pentavalent antimonials frequently fail to cure cutaneous, mucocutaneous, and visceral leishmaniasis, and characteristically fail to cure diffuse cutaneous We have determined the in vitro sensitivity of clinical isolates of Leishmania to pentavalent antimony to determine if inherent drug resistance of the parasite is responsible for treatment failures in human beings. Intracellular amastigotes resulting from promastigote-initiated infection of human macrophages were exposed to pentavalent antimony for 6 days at 34.5–35°C. Amastigotes from clinically sensitive simple cutaneous lesions exhibited a range of in vitro sensitivity. Four strains were ≥90% eliminated and two strains were 70–75% eliminated in vitro by concentrations of antimony (15–20 µg Sb/ml), comparable to peak achievable serum levels in humans. Amastigotes from initially clinically resistant simple cutaneous lesions showed a wider range of sensitivities. Five strains were ≥90% eliminated, but one strain was only 40% eliminated and another strain was completely insensitive in vitro. The clinically resistant diffuse cutaneous strain was 61% eliminated. The techniques described herein permit determination of the in vitro antimicrobial susceptibility of Leishmania from all major human forms of leishmaniasis. The data from this series indicate that in a minority of initially resistant cases, parasite resistance to the drug may be contributing to clinical resistance, and use of non-antimonial drugs might be recommended for future therapy.

Routine stool examinations for eggs and parasites have been recommended for Southeast Asian refugees seeking medical care for any reason. Calculations show that the direct dollar cost of diagnosis and treatment of pathogenic intestinal parasites in asymptomatic adults exceeds the direct dollar cost of disease prevented. However, it is also recognized that a more definitive analysis would require presently unavailable data on morbidity and trans-mission rates in untreated parasitized adults. Final decisions on screening benefits should consider, but not be limited to, direct dollar cost considerations.

The effects of benzimidazole anthelmintics in murine strongyloidiasis were examined. Thiabendazole 50 mg/kg daily produced a 91% reduction in the numbers of Strongyloides ratti larvae in the feces. A similar suppression was seen when thiabendazole was given during the intestinal phase, but no effect was noted when the drug was administered during the phase of larval migration. Thiabendazole had no effect on larvae in the skin or lungs, did not inhibit maturation of worms, and did not expel adult worms from the gut, but did reduce fecundity of adult worms in the intestines by 84%. Mebendazole and cambendazole 50 mg/kg daily totally suppressed excretion of S. ratti in the feces. A similar suppression was seen when the two drugs were given during the phase of larval migration or during the intestinal phase. They had no effect on larvae in the skin, and the reduction in larval numbers in the lungs was not statistically significant. When given during the migratory phase and early intestinal phase, they reduced the numbers of fourth stage larvae recovered from the gut by 95%. Mebendazole and cambendazole totally eliminated intestinal adult worms. Dose response studies indicated that in terms of the orally administered dose, cambendazole was 100–1,000 times more active than mebendazole. Thiabendazole and mebendazole had no significant effect on S. stercoralis larvae in the muscles. In contrast, cambendazole 50 mg/kg daily for 4 days eradicated S. stercoralis larvae from the muscles. It is concluded that cambendazole may have significant advantages over both thiabendazole and mebendazole in the treatment of strongyloidiasis.

Antimicrofilarial immunity was studied in Dirofilaria immitis-infected doges in order to better understand amicrofilaremic filariasis in man. Sera from dogs with amicrofilaremic infections contained IgG antibodies specific for microfilarial surface antigens detectable by immunofluorescence and in vitro leukocyte adherence. In vivo immune mechanisms were studied by injecting 51Cr-labeled microfilariae (MF) into infected and uninfected dogs. Injected MF were concentrated in lung, liver, spleen, and kidneys of normal and microfilaremic dogs, but circulated throughout the 5-hour study period. In contrast, injected MF were rapidly cleared (15–30 min) from the blood of amicrofilaremic-infected dogs. Tissue radioactivity and histopathology indicated that injected MF were trapped and destroyed in the lungs of these dogs. Antibody-dependent clearance and destruction of MF is a potent antihelminth effector mechanism in canine dirofilariasis. Similar events are likely to occur in amicrofilaremic filariasis in humans.

Examination of 75 blood samples (Knott preparation) collected in Puerto Inírida, Coco, and Pajuil, in the Comisaría del Guainía, Colombia, disclosed 26 microfilaria carriers. Eighteen persons harbored only Mansonella ozzardi microfilariae, three were infected with M. ozzardi and Dipetalonema perstans and five harbored only D. perstans. M. ozzardi infections were found in whites, and in Indians belonging to the Curripaco, Puinave, Tukano, Guanano and Saliva tribes, but D. perstans was found only in the Curripaco Indians. Numbers of circulating microfilariae (mf) were low, 73% of the carriers had less than 200 mf/ml of blood: persons who harbored only D. perstans had less than 310 mf/ml. These results confirm the presence of D. perstans in Colombia, and suggest that its prevalence and distribution in the Comisaría del Guainía and neighboring areas may be far greater than has been hitherto suspected.

Seventy-four villages in eastern Sierra Leone, West Africa, many having a recently developed rice swamp, were surveyed for the presence of schistosomiasis and onchocerciasis, and their vectors. Prevalence rates for Schistosoma haematobium and S. mansoni were low, although the infections were widespread. There is some evidence that S. mansoni is extending its range in Sierra Leone although this is problematical because of the apparent absence of Biomphalaria pfeifferi, the recognized snail vector, from areas where the disease now occurs. The characteristics of the rice swamp environment now being created in Sierra Leone are described and results of snail collections, which were with few exceptions small, are presented. Reasons for the apparent unsuitability of the developed rice swamp as a snail habitat are discussed. Onchocerciasis was found in all villages and the prevalence rate, almost 50%, was high. The rice swamp is not a suitable breeding site for Simulium damnosum s.l., but the study area is crossed by several major rivers and all villages in the area are within flying distance of potential breeding sites. There was no positive evidence that expansion of swamp rice farming will increase the incidence of water based/related diseases but a control program for onchocerciasis, which is a major rural health problem, would seem to be a national priority.

Six Schistosoma mansoni strains from Belo Horizonte (three from patients with the toxemic form of schistosomiasis and three from patients with the chronic intestinal form) have been experimentally compared. The following characteristics of infection were analyzed in the laboratory in mice: length of prepatent period, infectivity, total and differential white blood cell count, recovery of eggs in tissues, distribution of eggs in the viscera, and response to specific treatment. While significant differences existed among these six strains, those from patients with the toxemic form did not present a characteristic behavior that could clearly differentiate them from strains from non-toxemic patients. These results strongly suggest that the development of the toxemic form in man is not due to specific characteristics of the S. mansoni strain.

Developing larvae of Schistosoma mansoni migrate through various tissues en route to the liver and mesenteric veins of their definitive host. Regional (lymph node) and systemic (spleen) blastogenic responses to cercarial, adult and egg antigens were measured in CBA/J mice at various times after exposure to normal or irradiated S. mansoni cercariae. Among the separate lymph node groups studied were those draining the tail, thoracic region, intestines, head and neck, and the pelvis. Blastogenic responses were assayed by a micromethod requiring 105 cells in 20 µl volumes per culture. Up to 5 weeks post-cercarial exposure the pattern of responses in lymphoid tissues of infected mice coincided with the migratory route of the parasites. Following oviposition, cellular reactivity was pronounced in all lymph node groups. The reactivity of mice exposed to irradiated cercariae followed a pattern suggestive of a sustained antigenic stimulus only in the nodes draining the tail and lungs. Splenic (systemic) reactivity was roughly comparable between the two exposure groups. These data show the independence and vast differences in the host regional responses following normal or irradiated cercarial exposure.

Rabbits were infected with Schistosoma japonicum of Japanese origin between 1973 and 1979. The distribution of lesions and eggs in the small intestine and colon changed significantly twice during that period, and the number of eggs per worm pair passed in the feces changed at least once. The shift in egg distribution and that in egg passage occurred at different times and appeared not to be causally related. The number of eggs per worm pair retained in the tissues of chronically infected rabbits was consistently greater in rabbits with colonic bilharziomas. We postulate that differences in the schistosome population were responsible for the alterations in worm behavior. These differences may have been caused by the introduction of new isolates from the field, or by selection during laboratory passage.

Studies have been done to determine the levels of human urinary granulocyte colony-stimulating factor in Egyptian patients with active bilharziasis. Colony-stimulating factor levels were measured by a semi-solid tissue culture colony assay with murine bone marrow as the target cell source. The levels in urine from patients with bilharziasis (mean 118) were found to be significantly elevated above control values found in normal human urine (mean 72) derived from the same population. This is the first demonstration of an effect of parasitic infection in man on the granulocyte regulatory system, and opens the way for future studies in this area.

Three cases of cerebral lesions due to Paragonimus mexicanus in Costa Rica are reported, two of which were fatal. At autopsy a hemorrhagic, well circumscribed lesion was found in the hemispheres which microscopically consisted of a recent hemorrhage surrounded by a halo of eosinophils, with giant cell granulomas and Charcot-Leyden crystals. Eggs of P. mexicanus outside the brain were demonstrated in both fatal cases—in an eosinophilic pericarditis in one and in the other in multiple lesions of the liver and lungs. The third patient had a hemorrhagic cerebral lesion which was surgically evacuated; the patient recovered. Eggs were demonstrated in serial sections of the material resected.

Bracken Cave, a large natural cavern located 25 miles northeast of San Antonio, Texas, serves as nursery roost for millions of Mexican free-tailed bats (Tadarida brasiliensis). Ten days after spending several hours in the cave in early May 1979, three graduate students presented with signs and symptoms compatible with acute pulmonary histoplasmosis. A study was initiated to determine the presence and location of Histoplasma capsulatum in the cave and its inhabitants. The fungus was cultured directly from guano at five of nine sites sampled. Sentinel mice left for several hours at one of three positive sites developed histoplasmosis within 30 days after exposure. Autopsy was done on a total of 28 bats and their lungs, liver and spleen were cultured for viable H. capsulatum. In addition, sera from 58 bats were tested for antibodies to H. capsulatum, using a double diffusion test employing commercial reagents. All bat cultures and sera were negative. We conclude that the students were infected by massive exposure to viable H. capsulatum in aerosols created by disturbing guano deposits near the mouth of the cave. Tadarida brasiliensis contributes to a suitable environment for fungal proliferation, but does not appear to play an active role in the maintenance or dissemination of the fungus in Bracken Cave.

The IgM and IgG responses of 103 patients from the Pescadores Islands of Taiwan with typical signs and symptoms of scrub typhus, from whom Rickettsia tsutsugamushi had been isolated, were studied by the indirect microimmunofluorescent antibody test. Some aspects of the non-antigen specific cellular response were also investigated in a subset of these patients. Two distinct types of anti-rickettsial antibody responses were encountered. In 78 patients (Type 1 responders) the initial response, generally appearing by 8 days after onset of illness and rapidly increasing in titer, was IgM. IgG did not appear until 12 days and increased in titer more slowly. In 25 patients (Type 2 responders) the initial response, detectable by 6 days, was IgG, while the IgM response, detectable in only 16 of these patients, was variable in development and persistence. The IgA response, tested only in six patients of each group, was transient and occurred almost exclusively in the Type 1 responders. In later convalescence (>40 days after onset) IgG was the predominant anti-rickettsial antibody class in both groups and lasted approximately 1 year. The specificity of serological reactions towards the Gilliam, Karp, and Kato serotypes was more clearly shown in the IgM response of both groups of patients. During the course of the study, 14 patients from both groups exhibited serological evidence of subsequent reinfection, not accompanied by clinical disease. The cellular response was characterized by depressed levels of activated T cells (A-T cells) during acute illness (0–7 days post onset) and the early phase of convalescence (8–15 days after onset) in the Type 1 responders, and by elevated A-T cell levels in both groups during the later stages of recovery. Type 1 and Type 2 responders also differed in age and in the clinical manifestations of disease. Type 1 responders were younger, exhibited a higher incidence of rash and conjunctivitis, and a somewhat greater incidence of transient fever and relapse, following tetracycline or doxycycline therapy. Type 2 responders exhibited a higher incidence of generalized lymphoadenopathy. These results suggest that the Type 1 response reflects primary infection, while Type 2 indicates reinfection. The Type 2 response was comparable to that of the 14 cases of reinfection documented only by their antibody response. It is concluded that reinfection with R. tsutsugamushi is a relatively common occurrence in highly endemic areas, and that cell-mediated immunity, as evidenced by marked A-T cell responses in both patient groups, may play an important role in recovery from scrub typhus.

During July–September 1980, an epidemic of acute hemorrhagic conjunctivitis (AHC) occurred in several refugee camps and transit centers in Southeast Asia. Of 2,356 refugees examined in Bangkok, 200 (8.5%) had conjunctivitis, including 116 (58%) with hemorrhagic signs. Because increasing numbers of refugees were arriving in the United States with conjunctivitis, a program of surveillance and control was implemented. Enterovirus 70, not previously reported from patients in the Western Hemisphere, was cultured from four arriving refugees. A fourfold rise in titer to enterovirus 70 was found in 10 others, either in the United States or Thailand. After control measures were instituted, the prevalence of conjunctivitis in arriving refugees declined from 49.8 per 1,000 to 3.8 per 1,000. Follow-up of cases after arrival in the United States revealed only one possible secondary case. Extensive epidemics of AHC in the Western Hemisphere are most likely to occur following importation into the humid, coastal areas of Central and South America.