The American Journal of Tropical Medicine and Hygiene - Volume 46, Issue 3, 1992

Ladies and gentlemen, colleagues and friends, I have two good reasons to be delighted to introduce this year's Presidential address. First, of course, is that our President, Scott Halstead, is an old friend and mentor-indeed, it seems that hardly a Thanksgiving went by in Bangkok without Scott sharing our tom yam and turkey. Secondly, I have read his prepared speech, and I can assure you that it is sublime.

Scott began his life in a time zone opposite this one and over the ensuing 60 years, he, his household goods, and his family have repeatedly careened to and fro between Asia and the northeast United States. However, it can reasonably be argued that through it all Scott has simply been following his destiny. His parents were Methodist missionaries in Lucknow, India, where Scott was born and raised as a toddler. In an article written on their return to New York, a local newspaper referred to Scott's father as a “Young Exponent of the Ghandi Movement.”

Nearly forty years ago, the American Society of Tropical Medicine and Hygiene (ASTMH) was formed from its parent societies, The American Society of Tropical Medicine (ASTM) and the National Malaria Society (NMS). The Tropical Medicine Society was itself nearly 50 years old, having been founded in 1903 by several clinical faculty members of Philadelphia medical schools who wished to learn and teach more about the diseases of the tropics and to stimulate research on them. It may surprise some to learn that our American Society is four years older than its British counterpart, the Society of Tropical Medicine and Hygiene, which was instantly larger than our fledgling Society and has been under royal patronage since 1921.

At the dawn of what some would call “The American Century,” there is little reason to doubt that our Philadelphia founding fathers were influenced by the recent successful conclusion of the Spanish-American War and the US acquisition of and responsibility for new territorial possessions in the Caribbean and the Far East.

The Volunteer Collaborator Networks (VCNs) of Latin America are one of the oldest and most successful examples of community participation in malaria control. They are made up of unpaid community volunteers, known as Volunteer Collaborators, who are selected by their neighbors and are trained and supervised by a member of the National Malaria Service (NMS). When a febrile patient visits the home of a Volunteer Collaborator, the volunteer worker takes a thick blood smear, completes a patient report form, and administers a presumptive treatment for malaria. The blood smear is examined in an NMS laboratory, and if malaria parasites are found, a radical or curative treatment is forwarded to the Volunteer Collaborator so that it can be administered to the patient. There is no charge for either the blood smear or the antimalarial medication.

The VCN of Guatemala was established in 1958. Currently, more than 5,000 Volunteer Collaborator posts are operating throughout the malarious areas of the country. The volunteers range in age from 12 to 76 years old and 61% are men. Approximately 15% have no formal education, and only 27% have a sixth grade or higher education. The median length of service is 35 months (range three months to 26 years); 33% have worked for five or more years. Male Volunteer Collaborators had significantly lower turnover rates than females, as did married Volunteer Collaborators when compared with single volunteers. An inverse relationship was noted between the amount of education a Volunteer Collaborator had and his length of service.

With modifications tailored to meet the objectives of a malaria control program and the local epidemiologic setting, the VCN can serve as an excellent model for community participation in malaria case detection and treatment in other regions of the world. In particular, in areas where the primary goal of the malaria program is to prevent mortality and morbidity through the provision of readily accessible, appropriate drug therapy, VCNs are an attractive alternative to self-medication and an effective adjunct to treatment of malaria at health posts which are often located at a considerable distance from the patient's village. Experience gained with this system can be valuable in developing approaches to community involvement in other efforts to improve the health of villagers in developing countries.

To evaluate the effectiveness of the Volunteer Collaborator Network (VCN) of Latin America as a community-based malaria case detection and treatment system, we conducted a study of the VCN of Guatemala. Volunteer Collaborators took 72.6% of all blood smears and identified 81.3% of all malaria cases reported by the Guatemalan National Malaria Service. The average volunteer treated 5.8 patients per month (range 0–32.8). In contrast, passive case detection (PCD) posts in government hospitals and health centers treated an average of 12.5 patients per month (range 0.5–91.4). The slide positivity rate of blood smears taken by Volunteer Collaborators was 16.2% compared with 9.7% for PCD posts in health centers and 10.3% for malaria workers during active case detection. The average delay between the date a blood smear was taken and examined ranged from 18.1 days on the Pacific coastal plain to 26.3 days in the less accessible northern region of the country. An additional 14.5 to 47.6 days elapsed before the radical treatments were initiated in these two regions. Seventy percent of the patients completed their radical treatments.

In a survey conducted on the Pacific coastal plain of Guatemala, of 1,021 patients with chills and/or fever who believed they had malaria, 20.0% had visited a Volunteer Collaborator and 4.9% were treated at a government health center. Thus, the PCD network detected only 25% of all patients with symptoms suggestive of malaria. Most of the remaining patients treated themselves with antimalarial medications purchased in stores and pharmacies, but less than 15% of these patients used adequate courses of therapy. Furthermore, the rate of detection of symptomatic patients with malaria varied considerably from one community to another. Thus, data from the VCN are probably most useful when groups of communities or geographic areas are stratified for malaria control activities because at this level, variations between individual Volunteer Collaborator posts will be minimized. In spite of these problems, the VCN remains an excellent source of epidemiologic data for malaria control programs and the most practical means available for providing timely, appropriate antimalarial therapy to febrile patients in rural areas.

Three hundred sixty-three fecal specimens were collected from infants and young children with gastroenteritis over a 13-month period in Jeddah, western Saudi Arabia. Rotavirus was detected in 46% of the 363 specimens tested using an enzyme-linked immunosorbent assay (ELISA), and in 40.7% of 113 specimens using a latex agglutination test. One hundred nine of the 113 specimens that were positive by the latex agglutination test were also positive by ELISA. Electron microscopy was used to examine some specimens to demonstrate the presence of the virus. Rotavirus was detected throughout the 13-month study period, with an increase in the frequency of infection in the cooler months. Infection with this virus was more frequent among infants and children less than two-years old, with a maximum incidence among children 13–15 months old. In the 363 stool specimens tested, rotavirus was found in mixed infections with bacteria in 0.44%, with parasites in 1.31%, and with yeast in 0.66%.

Serologic surveys for Toxocara canis and Strongyloides sp., as well as stool examinations for intestinal parasites, were conducted in a home for mentally retarded adults. Evidence of parasitic infection was found in 30 (28.3%) of 106 residents; nine (8.5%) had positive toxocaral serology (enzyme-linked immunosorbent assay[ELISA]), 1 (0.9%) had positive serology for Strongyloides sp. (ELISA), and 21 (19.8%) had parasites in stool (including Strongyloides stercoralis in the patient with positive serology). Most of the residents with positive toxocaral serology lived in the same apartment and used to play with dogs. Parameters found to be significantly associated with positive toxocaral serology were pica behavior and eosinophilia (P < 0.05). Mental retardation requiring institutionalization appears to be a risk factor for toxocariasis and other parasitic infections in adults as it is for children.

Two species of sand flies were collected by various methods from sites in the Dominican Republic. Lutzomyia cayennensis hispaniolae was the more common of the two. It was found in wooded habitats from sea level to an elevation of 442 m. This species was observed feeding on lizards (Anolis sp.) in the wild. In the laboratory, it fed only on lizards and only under lighted conditions. The other species, Lu. christophei was only found in the vicinity of seven leishmaniasis case sites. It readily fed on or probed rodents and humans. Although no naturally infected sand flies were collected, in the laboratory Lu. christophei was readily capable of transmitting the Dominican Leishmania parasite to uninfected BALB/c mice. We collected 167 specimens of three species of rodents and three Herpestes auropunctatus (mongoose) from the vicinity of two case sites. All four species are non-endemics introduced in post-Columbian times. Although we were unable to isolate parasites from any of these specimens, four of 44 Rattus rattus from one case site were seropositive for antibodies against Leishmania by indirect fluorescent antibody testing. This represents the first report of transmission of the Dominican Leishmania parasite by a sympatric species of sand fly and suggests that commensal rodents may play a role in the epidemiologic cycle.

Central nervous system toxoplasmosis is a major opportunistic infection in patients with acquired immunodeficiency syndrome. The standard therapy for this infection is pyrimethamine (PYR) and sulfonamides. To assess in vivo if PYR alone could adequately treat toxoplasmosis, a murine model of acute toxoplasmosis was used. The CD1 strain of mice was infected intraperitoneally with 104 parasites of the RH strain of Toxoplasma gondii. Pyrimethamine was administered in mouse chow at concentrations of 0, 0.03125, 0.0625, 0.125, 0.25, or 1.0 mg of PYR/g of food, which provides the following daily PYR dosages: 0, 6.25, 12.5, 25, 50, and 200 mg/kg/day. No sulfonamides were administered. Serum PYR levels proved more accurate than mg of PYR/g of food in predicting survival. Mice with serum PYR levels ≥ 500 ng/ml (2 µM) survived and had no parasites present on peritoneal lavage. Mice with serum PYR levels < 100 ng/ml (0.4 µM) had a 100% mortality rate and the average parasite count was 3 × 107 organisms in the lavage fluid. At a PYR level of 370 ng/ml, six of 11 mice survived and the lavage fluid contained 2.5 × 105 organisms. Previously, using 3H-uracil in an in vitro assay, PYR at a concentration of 500 ng/ml was shown to be as effective in inhibiting Toxoplasma growth as the combination of PYR (100 ng/ml) and sulfonamides 25 µg/ml). These data suggest the potential usefulness of PYR for monotherapy of toxoplasmosis and are consistent with previously described in vitro assays.

The presence of circulating microfilariae has been associated with alterations in B and T cell functions. In this study, we compared the influence of diethylcarbamazine (DEC) and ivermectin on filarial antigen-specific immune responses in a Haitian population. Both drugs were effective at reducing microfilaremia levels to less than 10% of pretreatment levels for up to one year. This reduction in microfilaremia was associated with two phases of altered cellular responsiveness monitored with in vitro assays. Five days post-treatment, cellular proliferation in response to both filarial and nonfilarial antigens was significantly increased, as was the background response in the absence of any antigen. At both nine months and one year post-treatment, the filarial antigen-specific reactivity of both DEC- and invermectin-treated patients was significantly increased over baseline levels. No differences were observed between the two treatment groups in terms of humoral or cellular reactivity to filarial antigens, despite evidence suggesting a role for DEC in adult worm killing. These results provide additional evidence that microfilariae modulate antifilarial immune reactivity.

Pentavalent antimonial compounds have been the mainstay of the treatment of visceral, cutaneous, and mucosal leishmaniasis for approximately half a century. Pentostam (sodium stibogluconate) is the pentavalent antimonial compound available in the United States (through the Centers for Disease Control). As dosage regimens for treating leishmaniasis have evolved, the daily dose of antimony and the duration of therapy have been progressively increased to combat unresponsiveness to therapy. In the 1980s, the use of 20 mg/kg/day (instead of 10 mg/kg/day) of antimony was recommended, but only to a maximum daily dose of 850 mg. The authors have concluded on the basis of recent efficacy and toxicity data that this 850-mg restriction should be removed; the evidence to date, which is summarized here, suggests that a regimen of 20 mg/kg/day of pentavalent antimony, without an upper limit on the daily dose, is more efficacious and is not substantially more toxic than regimens with lower daily doses. We recommend treating all forms of leishmaniasis with a full 20 mg/kg/day of pentavalent antimony. We treat cutaneous leishmaniasis for 20 days and visceral and mucosal leishmaniasis for 28 days. Our judgment of cure is based on clinical criteria.

A Plasmodium falciparum antigen gene coding for a 220-kD glutamate-rich protein (GLURP) has been cloned, and the 783 C-terminal amino acids of this protein (GLURP489–1271) have been expressed as a β-galactosidase fusion protein in Escherichia coli. The encoded 783 amino acid residues contain two areas of repeated amino acid sequences. Antibodies against recombinant GLURP489–1271, as well as against a synthetic peptide corresponding to GLURP899–916, and against a synthetic peptide representing the major glutamate rich repeat sequence from the P. falciparum ring erythrocyte surface antigen (Pf155/RESA) (EENV)6 were examined in 423 individuals (age range 30 days-78 years) living in a malaria holoendemic area of Liberia. In the 5–9-year-old age group, subjects with anti-GLURP489–1271 antibody concentrations greater than the mean value of the group had lower parasite densities than those with low antibody concentrations (P = 0.0151). High levels of anti-GLURP899–916 antibodies did not correlate with low parasite densities. However, high levels of anti-(EENV)6 antibodies were associated with significantly lower parasite densities in the 2–4-year-old age group (P = 0.0189). There was no correlation between the anti-GLURP489–1271 and anti-(EENV)6 antibody responses. The data provide indirect evidence for a protective role of antibodies reacting with recombinant GLURP489–1271 as well as with the synthetic peptide (EENV)6 from the Pf155/RESA.

A direct, double- and triple-staining immunoenzymatic method detected and differentiated sporozoites by color in Anopheles stephensi salivary glands and in mixed sporozoite slide preparations. A double-staining method used beta-galactosidase- and alkaline phosphatase-labeled monoclonal antibodies to the circumsporozoite (CS) proteins of Plasmodium berghei and P. falciparum in mosquito salivary glands. The CS proteins were distinguished clearly by the blue-green and red substrate products of beta-galactosidase and alkaline phosphatase, respectively. A triple-staining method differentiated by color among a mixture of P. falciparum and two strains of P. vivax sporozoites. Monoclonal antibodies to the CS proteins conjugated to beta-galactosidase (P. falciparum), alkaline phosphatase (P. vivax variant), and horseradish peroxidase (P. vivax predominant) readily color differentiated sporozoites by the blue-green, purple-blue, and orange-brown substrate products, respectively. This assay may have potential use in malaria transmission studies, genetic crosses of variant strains of plasmodia to determine assortment of CS antigen alleles, and as a technique to determine the fate of the CS antigen in infected mosquitoes.

The circumsporozoite (CS) protein of Plasmodium vivax consists of a central repeat region flanked by highly conserved non-repeat regions. Serum samples from 33 individuals with naturally acquired infections of P. vivax were tested for antibodies to four antigens representing the vivax CS protein. Three recombinant proteins containing different overlapping sequences in the non-repeat regions and either the entire central repeat region (vivax-1 and vivax-2) or two of the repeat sequences (vivax-3) were used as antigens in an enzyme-linked immunosorbent assay (ELISA). Antibodies to two other proteins, one (NS181 V20) containing the entire predominant repeat region (GDRAA/DGQPA) and the other (Pvk247) containing the variant repeat sequence (ANGAGNQPG) that was recently reported from Thailand were also measured by ELISA. Immunoglobulin G antibodies to the antigen representing the predominant repeat were present in 15% of the patients on the first day of treatment (day 0) and in 24% of the patients two weeks later (post-treatment). Six and 12% of the patients had IgG antibodies to the antigen containing the variant repeat on day 0 and post-treatment, respectively. A larger proportion of the sera had antibodies to the three antigens containing the non-repeat sequences; on the first day of treatment and two weeks later, 79 and 97% of the patients, respectively, had antibodies to vivax-1, vivax-2, and vivax-3. In this sample of Peruvians naturally infected with P. vivax, the most prevalent antibody responses were targeted to epitopes in the non-repeat region of the CS protein rather than to epitopes in the repeat region. The exact location of the non-repeat epitopes and their relevance to immunity to sporozoites deserve further investigation.

To determine the duration of immunity to Plasmodium vivax following immunization, six Saimiri sciureus boliviensis monkeys were vaccinated with irradiated sporozoites of P. vivax and challenged multiple times with sporozoites. Over a period of almost four years, complete protection from repeated challenge with infective sporozoites was demonstrated in one monkey; protection in two monkeys was obtained on eight of nine occasions, in one monkey on seven of nine occasions, in one monkey on six or nine occasions, and in one monkey on four of eight occasions. Five of six monkeys were protected against infection during the last six challenges. Inoculation with blood-stage parasites at the end of the trial indicated that all animals were susceptible to infection. These results suggest that protection against sporozoite challenge may be strongly reinforced by subsequent exposure to viable sporozoites.

The polymerase chain reaction was used to amplify the highly variable region of the kinetoplast minicircle of Trypanosoma cruzi directly in biological samples (feces of infected Triatomine bugs, blood samples of experimentally infected mice, and artificially infected human blood samples). Hybridization of the amplified DNAs with reference stocks representing different genotypes (natural clones) enabled us to characterize the stocks infecting the biological samples under study. The main interest of this new approach is the diagnosis of T. cruzi infection and simultaneous direct identification of the different natural clones circulating in vectors and mammalian blood without isolation of the stocks. The suitability of this technique for epidemiologic studies is also discussed.

To analyze the characteristics of Leptospira strains HY-1, HY-2, and HY-10, which were isolated from patients with leptospirosis in Korea in 1985, 12 monoclonal antibodies (MAbs) against strain HY-1 and six MAbs against serovar lai strain 017 were produced, and their properties were determined by the microscopic agglutination test. Genetic relationships among the leptospires were determined by restriction endonuclease DNA analysis. Three MAbs reacted with all strains of serogroup Icterohaemorrhagiae, but did not react with any strains of the other 10 serogroups. All MAbs reacted with strains 017, HY-1, HY-2, and HY-10 at nearly identical titers. Two MAbs reacted only with these four strains. These four strains also had the same restriction endonuclease cleavage patterns. Based on these results, strains HY-1, HY-2, and HY-10 were identified as serovar lai, which is one of the common serovars in China. It is suggested that serovar lai is one of the prevalent serovars in Korea, and that the Mabs produced in this study are useful for the accurate and rapid identification of this serovar.

Genomic DNA of Toxoplasma gondii was digested with the restriction endonuclease Hpa II and the resulting repetitive DNA sequences were visualized after electrophoresis on agarose gels and staining with ethidium bromide. Three repetitive DNA sequences were isolated and cloned in the plasmid pUC19. The recombinant plasmids (pTg8, pTg4 and pTg1) had inserts of 840, 440, and 180 basepairs, respectively. The estimated copy number of these cloned sequences in the T. gondii genome was approximately 800–1,000 for pTg4, 150–200 for pTg8, and 30–40 for pTg1. In dot-blot hybridization tests, pTg4 was able to detect as little as 80 pg of purified T. gondii DNA or 1,000 parasites in the presence or absence of 1.5 × 106 human or mouse leukocytes. No cross-hybridization was detected with 10 µg of either human and mouse DNA or 100 ng of DNA from other parasites (Eimeria tenella, E. acervularia, Trypanosoma cruzi, and Leishmania donovani), or among the three DNA probes. Each probe identified T. gondii tachyzoites in tissue (liver and spleen) obtained from experimentally infected mice in which histologic damage was detected. In addition, early detection of T. gondii in brain tissue and blood samples was possible with the pTg4 probe.

The multicellular parasite Schistosoma mansoni undergoes complex physiologic changes during development from infective cercariae to adult worms in the mammalian host. The present study examined changes in protein kinase C (PKC) activity in S. mansoni during parasite maturation. Activation of PKC required Ca+2, phosphatidylserine, and either diacylglycerol or phorbol ester similar to mammalian PKC enzyme. A nine-fold increase in total PKC activity was found in adult worms as compared with larval parasites. Transformation of infective cercariae to parasitic schistosomula was associated with translocation of PKC activity from the cytosolic to membrane fraction. Tegumental extracts demonstrated significant PKC activity, suggesting a signal transduction system in the surface of the parasite. These data indicate that PKC activity is differentially expressed during parasite development and may have critical roles in regulation of cellular events in S. mansoni.

Humans with inherited abnormalities of hemoglobin (Hb) synthesis have less frequent and less severe infections of malaria. This study sought to determine if karyotypic variation in the owl monkey was expressed as differences in Hb moieties and if it offered a selective advantage in susceptibility to malaria. Five karyotypes of owl monkey were evaluated on the basis of the electrophoretic mobility of their major and minor Hb components. The results of 40 owl monkeys of different karyotypes demonstrated that statistically significant differences exist among karyotype I animals and those with karyotypes II, III, and V, particularly with regard to their HbA2 concentrations. This finding is of interest in light of the fact that karyotype I animals are considered to be less susceptible to infection with human strains of Plasmodium falciparum than karyotypes II, III, and V, which are viewed as being highly susceptible.