The American Journal of Tropical Medicine and Hygiene - Volume 39, Issue 3, September 1988

Last April I received a telephone call from Lawrence K. Altman, who identified himself as a science writer, and who wanted to discuss two subjects dealing with material that had appeared on the Editor's pages of the JOURNAL. We had a long, usually amicable, discussion and a few weeks later one of these topics was noticed by him in a newspaper article. Excerpts are:

“Another problem involves the failure to provide promised backup data for important assertions.

“Two years ago a paper in The American Journal of Tropical Medicine and Hygiene reported that acute respiratory infections were the leading cause of death in children in developing countries. The paper relied heavily on another paper the Journal said would be published later. But the Journal did not publish the second paper and the reference in the first paper still stands.

“Dr. William D. Tigertt, the Journal's editor, said he did not publish the second paper because of differences of opinion about its writing style, not its scientific merit.

Synthetic, 21-base, DNA probes to the genome of Plasmodium falciparum were either 32P-labeled or enzyme-conjugated for comparative field studies. The sensitivity of both probes was compared with microscopy in the examination of blood samples from 97 Thai villagers, 47 Thai Rangers, and 19 malaria-free Bangkok residents. The probes were also used to monitor the therapeutic response of 18 of the Rangers during 7 days of treatment. The probes proved highly specific. Both probes had lower limits of detection of about 100 parasites per µl blood. Thus, the low parasite densities in partially immune villagers from an endemic area were often missed, while higher parasite densities in the nonimmune Rangers were usually detected. As monitors of response to treatment, the probes paralleled microscopy in identifying reversion from positive to negative parasitemia. The enzymelabeled DNA probe as shown to perform similarly to the radiolabeled probe in populations with different malarial immune status and during curative treatment.

Most adults in highly malarious areas have antibodies to the repeat region of the circumsporozoite protein of Plasmodium falciparum. To determine if a T cell epitope on the repeat region stimulated T cell help for this antibody, we used R32tet32, a recombinant construct derived from the repeat region of the circumsporozoite protein of P. falciparum, to stimulate in vitro mononuclear cells from residents of an area hyperendemic for malaria. Three groups differing in the length of time they had resided in a malarious area were studied. The percentage of individuals in each group who had positive antibody responses to R32tet32 increased with increased exposure to malaria. However, antibody positivity was not correlated with in vitro lymphocyte proliferation responses to the antigen. Lymphocytes from 79% of the individuals showing serum antibodies to R32tet32 failed to respond in a lymphocyte transformation assay, suggesting that T cell helper activity in these individuals was based upon the recognition of a T cell epitope not located within this peptide.

The activity of desferrioxamine (Desferal) and desferrithiocin (a newly developed oral iron chelator) was evaluated against the liver stage of Plasmodium yoelii and P. falciparum in the rodent and the human hepatocyte in vitro culture system. The two iron chelators were found to inhibit the liver schizogony of both the rodent and the human Plasmodium species at concentrations achievable in vivo. P. falciparum proved to be more sensitive (ic 95% below 20 micromol/l than P. yoelii (ic 95% 50–100 micromol/l). As assessed by electron microscopy, drug administration was associated with focal clarification of the cytoplasm thought to be reversible.

As desferrioxamine and desferrithiocin are known to be equally active on the blood stage of rodent and human plasmodia, iron chelators are deserving of further investigation as potential alternative candidates to existing drugs for radical cure of malaria.

Antibody responses to malarial antigens were determined in 614 serum samples collected from the Wopkaimin population of the Star Mountains of Papua New Guinea. In point prevalence surveys made in 1982–1983, 33.7% of the persons examined were infected with Plasmodium falciparum, P. vivax, or P. malariae. Of these, 72.9% were infected with P. falciparum. In a standard fluorescent antibody test, highest level responses were to P. falciparum, followed by P. malariae, P. vivax, and P. ovale. A strong correlation was found between results of the fluorescent antibody tests and those obtained in an enzymelinked immunosorbent assay using P. falciparum antigens. The failure of immune responses to eliminate these species of Plasmodium in this highly isolated population is discussed.

The cause of fetal loss in malaria is not known. We report that a small (1.5–5.0 µg) intravenous dose of recombinant human tumor necrosis factor (TNF) caused fetal death and abortion in 16 day pregnant mice that were carrying low densities of Plasmodium vinckei. In contrast, 50 µg human TNF did not cause fetal death or abortion in uninfected 16 day pregnant mice. Endogenous TNF, which was not detectable in plasma of low parasitemia animals, pregnant or not, was present (1.6 ± 0.9 ng/ml) in samples from malarial pregnant mice when, on day 17, parasitemia was high and the first signs of impending abortion were evident. No TNF was detectable in the plasma of uninfected mice at day 17 of pregnancy.

A small dose of TNF also caused fetal death in 16 day pregnant mice that had received an intravenous injection of Coxiella burneti extract 9–10 days earlier. Thus, TNF-induced abortion may occur in a range of infections in which systemic macrophage activation occurs and a trigger for TNF release is present.

Pyrazolopyrimidines, particularly allopurinol, allopurinol riboside, and other purine analogues, show promise as experimental therapeutic compounds for the treatment of leishmaniasis. The combination of these agents with pentostam may produce an improved therapeutic effect. We report here on strong synergistic activity between pyrazolopyrimidines and pentavalent antimonials in a human macrophage tissue culture system infected with Leishmania donovani and L. braziliensis.

This paper addresses the issue of how physiological properties of Leishmania determine the pattern of development of disseminated leishmaniasis in the mammalian host. It presents direct experimental evidence from in vivo studies that species of Leishmania differ in their capacity to multiply in cutaneous and visceral sites which results in differences in the pattern and rate of development of leishmaniasis. It was found that Leishmania mexicana amazonensis begins to multiply in the cutaneous site of inoculation within 7 days. Parasites, detected in the liver and spleen at 4 weeks, increased 100-fold during the next 4 months. However, the slow multiplication of L. mexicana amazonensis in the liver and spleen was more apparent than real. Parasites implanted in those organs of athymic nude mice by an intravenous injection were rapidly eliminated with a half-time of 16 hr. Thus, the parasites found in small numbers in the liver during the development of disseminated cutaneous disease in mice are most likely those which have been recently removed from the blood. Those few parasites that are not removed from the blood can establish metastatic foci in distant cutaneous sites, and replicate progressively once there.

Studies on the phlebotomine fauna related to the leishmaniasis endemic foci of the Colombian Pacific Coast were carried out in the municipalities of Tumaco and Buenaventura. In Inguapí del Guadual, Tumaco, Lutzomyia trapidoi and Lu. gomezi were the predominant anthropophilic species; Lu. panamensis and Lu. hartmanni were less frequent. In Bajo Calima, Buenaventura, Lu. trapidoi represented over 94% of the anthropophilic sandflies. Continuous sampling from 1800 to 0600 hours in Inguapí del Guadual demonstrated that Lu. trapidoi bites mainly at dusk and dawn whereas Lu. gomezi remains active throughout the night. In Inguapí del Guadual, promastigotes were found in 0.1% (2/2, 305) of Lu. trapidoi, 0.2% (3/140) of Lu. gomezi, and 0.2% (1/424) of Lu. panamensis samples collected. In Bajo Calima, 1.9% (8/429) of Lu. trapidoi were found to be infected. Leishmania braziliensis panamensis, the most common Leishmania subspecies in the human population of this endemic focus, was isolated from 1 Lu. trapidoi from Inguapí del Guadual. Parasitological and entomological findings suggest that Lu. trapidoi could be the main vector of Leishmania in these areas, although Lu. gomezi and Lu. panamensis were also predominant.

Six Leishmania isolates from 3 indigenous Kenyans (2 isolates from one patient) and 2 Canadian visitors in Kenya were characterized by cellulose acetate electrophoresis. The isolates were compared among themselves and with reference strains of Leishmania donovani, L. aethiopica, L. major, L. tropica, and L. arabica using 9 enzymes: malate dehydrogenase (MDH), malic enzyme (ME), phosphogluconate dehydrogenase (6PGD), glucose-6-phosphate dehydrogenase (G6PD), aspartate aminotransferase (ASAT), adenylate kinase (AK), mannose phosphate isomerase (MPI), glucose phosphate isomerase (GPI), and phosphoglucomutase (PGM). Enzyme migration patterns of isolates from the 3 indigenous Kenyans were indistinguishable from those of 2 L. tropica reference strains. The isolates from the 2 Canadians yielded migration patterns of 7 enzymes that were indistinguishable from those of 2 L. tropica reference strains. However, migration patterns of 2 enzymes, PGM and ME, differed from all migration patterns of the 10 reference strains. Balb/c mice were inoculated with stationary phase promastigotes cultured from 3 stabilates from the lesions of 2 of the Kenyan patients. The mice developed no gross pathological lesions in 6 months time.

All of the study patients developed cutaneous leishmaniasis while living in or visiting districts in Central and Rift Valley Provinces, Kenya. This is the first report of human cutaneous leishmaniasis caused by L. tropica indigenous to Africa south of the Sahara.

A standardized enzyme-linked immunosorbent assay (ELISA), performed directly on monolayers of mouse peritoneal macrophages or L 929 fibroblasts, was used to evaluate the activity of chemotherapeutic agents against four different stocks of Trypanosoma cruzi. Absorbance readings, performed in an automatic ELISA reader, were directly related to the number of intracellular parasites as determined by microscopic examination of tissue culture slides run in parallel. Results were highly reproducible in replicate wells and in repeated experiments. Results with nifurtimox, ketoconazole, and formycin B, compounds known to have in vivo activity against T. cruzi, revealed that the ELISA technique was capable of detecting small dose-response variations in the rate of phagocytosis of different life cycle stages of T. cruzi by normal and activated mouse macrophages.

Entamoeba histolytica trophozoites were centrifuged into mucus gels harvested from in vivo loops of rat cecum and proximal colon. Frank ameba movement was not detected in the colonic mucus, but attenuated motility was measured in the cecal mucus. The harvested rat cecal mucus had significantly lower apparent viscosity and neutral glycoprotein concentration values than the colonic mucus. A shape factor method was developed to assess the motility of amebae in mucus gels and intact mucus blankets. Shape factor data obtained from harvested mucus gel and intact mucus blanket experiments indicated that such mucus severely attenuated trophozoite movement with the attenuation being greater with colonic than with cecal mucus. Entamoeba trophozoites are known to be able to generate a pseudopod force of 3.3 × 10-6 Newtons. Latex microspheres of the size range of Entamoeba trophozoites were forced through cecal and colonic mucus gels under gravity. Colonic mucus gels could withstand a force of 3.3 × 10-6 Newtons while cecal mucus could not, suggesting that the ameba movement that was observed in cecal mucus involved mechanical penetration of the mucus by the ameba pseudopodia and did not require prior gel dissolution by Entamoeba enzymes.

Immunoaffinity-purified antibodies against soluble Schistosoma mansoni egg antigens (SEA) were isolated from the sera of patients with schistosomiasis mansoni. Similarly, antibodies against Trypanosoma cruzi epimastigote antigens were obtained from sera of patients with Chagas' disease. These antibody preparations were used in culture to demonstrate the presence of anti-idiotypic T lymphocytes in peripheral blood mononuclear cell preparations from patients with either schistosomiasis mansoni or Chagas' disease, or with both of these infections. Only cells from patients with schistosomiasis or both infections proliferated upon exposure to the anti-SEA antibodies. Conversely, only cells from patients with Chagas' disease or both infections responded to anti-epimastigote antibodies. Western blot analysis of SEA and epimastigote antigens, developed by patients' sera or by immunoaffinity-purified antibody preparations, substantiated that anti-SEA immunoaffinity-purified antibodies only reacted with components of SEA, and anti-epimastigote immunoaffinity-purified antibodies only reacted with components of epimastigote antigenic preparation. These studies demonstrate the presence of anti-idiotypic T lymphocytes in the peripheral blood of patients with schistosomiasis or Chagas' disease which are specific for idiotypes generated during these infections.

To determine the effect of targeted field administration of oral chemotherapeutic agents on the prevalence, intensity, and morbidity of Schistosoma haematobium infections, we initiated a long-term school-based program in the Msambweni area of Kwale District, Coast Province, Kenya. Prior to treatment, 69% of the children examined (ages 4-21, n = 2,628) were infected; 34% had moderate or heavy infections (> 100 eggs/10 ml urine). Infected individuals were randomized to receive, during one year, either metrifonate (10 mg/kg × 3 doses) or praziquantel, (40 mg/kg × 1 dose). At the end of the first year, prevalence of infection fell to 19%; only 2% of the pupils remained in the moderately and heavily infected groups. Corresponding decreases in the prevalence of hematuria (54% in 1984 vs. 16% in 1985) and proteinuria (56% in 1984 vs. 26% in 1985) were noted. These were associated with significant declines in bladder thickening and irregularities noted during ultrasound examinations, but not with decreases in hydronephrosis. There was no significant difference in the post-treatment prevalence or intensity of infection after treatment with metrifonate as compared with praziquantel. These results demonstrate that field-applied chemotherapy with either agent offers a practical strategy for the control of S. haematobium infection and its associated morbidity.

We studied 39 patients envenomed by the Philippine cobra (Naja naja philippinensis). Neurotoxicity occurred in 38 cases and was the predominant clinical feature. Respiratory paralysis developed in 19 patients, and was often rapid in onset—in 3 cases apnea occurred within 30 min of the bite. There were 2 deaths, both in patients who were moribund upon arrival at the hospital. Three patients developed necrosis, and 14 individuals with systemic symptoms had no local swelling. Both cardiotoxicity and reliable nonspecific signs of envenoming were absent.

Bites by the Philippine cobra produce a distinctive clinical picture characterized by severe neurotoxicity of rapid onset and minimal local tissue damage.

This paper describes a case of severe encephalitis in a 3-year-old Panamanian boy infected with the Indiana serotype of vesicular stomatitis virus. The virus was recovered from the child's throat on the fifth day of illness and a rise in neutralizing antibody titer was demonstrated in paired serum specimens. This is the second report of childhood encephalitis associated with vesicular stomatitis virus infection. These suggest that infection with vesicular stomatitis viruses may cause severe disease. Human infection with vesicular stomatitis viruses is common throughout the tropical Americas.

This technical manual was produced in response to the recommendation of a World Health Organization Bi-regional Working Group of Filariasis. The contributors to this manual have produced an excellent, practical guide not only for those who plan, manage, and implement lymphatic filariasis control activities, but also for those in research whose projects include field studies.

The manual is organized into three parts. Part 1 is a very useful capsule of general information on lymphatic filariasis beginning with the life cycle and vectors of Wuchereria bancrofti, Brugia malayi, and B. timori. This is followed by the distribution, clinical manifestations, and available methods of diagnosis and treatment of lymphatic filariasis. This information should be of considerable assistance to those new to the field.

Part 2 outlines strategies for the control of lymphatic filariasis. It provides the planners and implementors of such projects the framework for community oriented strategies for lymphatic filariasis control programs.