The American Journal of Tropical Medicine and Hygiene - Volume 45, Issue 1, July 1991

Yellow fever once ranked among the greatest of human afflictions, conquered attempts at colonial settlement and economic development, and caused epidemics with much suffering in towns and cities as far north as Boston and Swansea. The conquest of yellow fever began in 1900 with Walter Reed's decisive investigations that proved transmission of the virus by Aedes aegypti, expelled public fear and confusion about causation, and provided a practical recipe for combating the disease. By 1927, the yellow fever virus had been isolated. Within a decade, tests were generated for measuring human immunity, and the French neurotropic and 17D live, attenuated vaccines were developed. Although discovery of the jungle cycle of yellow fever transmission in 1935 dispelled hopes of ever eradicating the disease, widescale use of vaccines in the 1940s and systematic efforts to subdue Ae. aegypti brought yellow fever under control.

Two Saimiri monkey vaccine trials have been conducted comparing four recombinant Plasmodium vivax circumsporozoite proteins and irradiated sporozoites. Only a small number of animals immunized with certain recombinants or irradiated sporozoites became fully protected against sporozoite challenge. Preimmunization and postimmunization plasma samples obtained from 30 monkeys on the day of challenge were tested in an in vitro assay based on sporozoite development into exoerythrocytic stages in primary cultures of Saimiri monkey hepatocytes. The percentage of inhibition was determined by comparison of the number of exoerythrocytic stages developing from sporozoites preincubated with a preimmunization and a postimmunization plasma sample of each animal. The plasma samples of the day of challenge of nearly all the immunized animals had a variable, but significant inhibitory effect, when compared with the corresponding preimmunization sample. We found no correlation between the degree of in vitro inhibition of liver stage development, and the in vivo protection against sporozoite challenge of individual animals. The variable results of the incubation of sporozoites with “normal” plasma of different animals indicates that the in vitro results were affected by plasma factors unrelated to anti-sporozoite antibodies.

Two hundred and seventy-five Orang Asli volunteers living in nine villages in the Pos Legap Valley of Perak State, penisular Malaysia, participated in a prospective study designed to characterize the epidemiological, parasitological, and entomological characteristics of Plasmodium falciparum, P. vivax and P. malariae malaria transmission. Prevalence rates for the three plasmodial species at initiation of the study ranged from 56% in the 0-4-year-old age group to 0% in individuals over the age of 40. Entomological surveys were conducted, enabling us to determine mosquito salivary gland-positive rates and entomological inoculation rates of 1.2 infectious mosquito bites per person per month for P. falciparum, 2.4 for P. vivax, and 0.3 for P. malariae. Cumulative incidence rates over the 16 weeks of the study, following radical cure of all volunteers, were 22.5% for P. falciparum, 12.7% for P. vivax, and 1.5% for P. malariae. The median baseline antibody titer against the immunodominant repetitive B cell epitope of P. falciparum or P. vivax circumsporozoite protein was significantly higher for volunteers who did not become parasitemic. Volunteers were selected for further study if they had evidence of being challenged with P. falciparum sporozoites during the study, based on a two-fold or greater increase in antibody titer against the immunodominant repetitive B cell epitope of the circumsporozoite protein. Resistance to infection was seen in six of 10 individuals who had high (> 25 OD units) baseline ELISA titers, compared with only three of 24 individuals who had low baseline ELISA titers (x 2 P < 0.02). A similar analysis for P. vivax did not show a significant correlation.

An analysis of Plasmodium falciparum-specific antibodies was performed in pairs of maternal and cord sera from Gabon, a region endemic for malaria. All paired sera (n = 59) had P. falciparum-specific antibodies. Immunofluorescence assays detected parasite-specific IgG1, IgG2, and IgG3 in 100% of the tested pairs (n = 26) and IgG4 in 42% of them. The titers of specific IgG2 and IgG3 were significantly lower in cord than in maternal sera. All maternal sera had specific IgM. Of the seven P. falciparum-IgM positive cord sera, six were associated with malaria-related histological placental changes (MRHPC). In addition, higher titers of specific IgG1 in maternal and cord sera and of specific IgG3 in cord sera were associated with MRHPC.

Similar P. falciparum antigens were recognized by cord and corresponding maternal sera in radioimmunoprecipitation and Western blot assays (n = 40). Sixteen of 20 cord sera and 15 of 20 paired maternal sera significantly inhibited in vitro parasite growth. The extent of inhibition did not correlate with the titer of specific antibodies.

These data confirm the very effective placental transfer of anti-malarial antibodies. The presence of IgM in some cord sera raise the question of intrauterine sensitization to malaria antigens.

An epidemiologic study of susceptibility to frequent and high-grade parasitemia by Plasmodium falciparum revealed that age-dependent acquired protection developed within a two-year period of exposure to hyperendemic infection pressure. The study was conducted in a single village in northeastern Irian Jaya, Indonesia, where half the residents were native to the province and the other half were transmigrants from areas of Java, where there is little or no malaria transmission. Five separate measures of susceptibility to the asexual parasitemia of falciparum malaria were derived from results of four months of biweekly surveillance of 240 volunteers. Increasing protection as a function of age among the Javanese was a consistent pattern among the five estimates of susceptibility. These age-dependent functions of protection were quantitatively parallel to those among life-long residents of Irian Jaya. When hurnoral immune responsiveness to ring-infected erythrocyte surface antigen (RESA) was measured by ELISA, a similar pattern emerged; the relative level of antibody to RESA increased as parallel functions of age among the two subpopulations. Acquired protective immunity against P. falciparum was not the cumulative product of many years of heavy exposure to antigen. Instead, the full benefit of protection appeared to develop quickly. The degree of protection was governed by recent exposure and age, independent of history of chronic heavy exposure.

The occurrence of malaria infections due to Plasmodium vivax and P. falciparum was monitored in a population of 3,023 people living in six contiguous villages in Kataragama, an area of endemic malaria in southern Sri Lanka, over a period of 17 months. The annual incidence of malaria in this population during the study period was 25.8%. Malaria attacks were clustered, occurring more frequently than expected in certain individuals and housing groups and less frequently than expected in others. In one of these villages, the distribution of cases was examined in relation to locality and to the type of house construction. There was a strong association between the malaria incidence and house construction, independent of location. The risk of getting malaria was greater for inhabitants of the poorest type of house construction (incomplete, mud, or cadjan (palm) walls, and cadjan thatched roofs) compared to houses with complete brick and plaster walls and tiled roofs. Houses that were better constructed had a significantly lower malaria incidence rate (10.5%) than those that were poorly constructed (21.2%; P < 0.01, by Student's t-test). There was also a significantly higher number of indoor resting mosquitoes collected from the poorly constructed houses than from those better constructed; the average (geometric mean) of mosquito densities found in houses of better versus poor construction were 0.97 and 1.89 per collection in the dry season, and 1.95 and 3.42 per collection in the wet season, respectively (P < 0.05 in both seasons). This indicated that the higher malaria risk associated with poorly constructed houses was at least partly due to higher human-mosquito contact among their inhabitants.

This study describes neuropsychiatric side effects in patients after treatment with mefloquine. Reactions consisted mainly of seizures, acute psychoses, anxiety neurosis, and major disturbances of sleep-wake rhythm. Side effects occurred after both therapeutic and prophylactic intake and were graded from moderate to severe. In a risk analysis of neuropsychiatric side effects in Germany, it is estimated that one of 8,000 mefloquine users suffers from such reactions. The incidence calculation revealed that one of 215 therapeutic users had reactions, compared with one of 13,000 in the prophylaxis group, making the risk of neuropsychiatric reactions after mefloquine treatment 60 times higher than after prophylaxis. Therefore, certain limitations for malaria prophylaxis and treatment with mefloquine are recommended.

Pentavalent antimony has been considered to be the standard treatment for leishmaniasis, but more recently, the orally administrable agent allopurinol ribonucleoside has been the subject of several clinical trials. In this study, these two agents were evaluated in patients with Ecuadorian cutaneous leishmaniasis. Patients were randomly assigned to the two treatment groups. The mean reduction in lesion size for the 28 patients treated with Pentostam (20 mg Sb/kg/day intramuscularly for 20 days) was 61%, 23%, and 11% after one, two, and three weeks, respectively. There was a wide range in the individual values, and some lesions markedly enlarged in the first week of therapy. An initially healed lesion was defined as one that had > 80% re-epithelialized by the 1.5-month post-treatment followup. All Pentostam patients demonstrated this degree of lesion resolution (100% initial healing rate), but one patient showed evidence of relapse at the three month followup resulting in a 96% complete healing rate for the 12 month observation period. Patients in the untreated control group demonstrated a strikingly high rate of healing with 9 of 12 patients having re-epithelialized all lesions after 1.5 months observation (75% initial healing rate). The mean reduction in lesion size for the untreated patients was 56%, 29%, and 25% after one, two, and three weeks, respectively. Twenty-one patients received allopurinol ribonucleoside (1, 500 mg QID) plus probenecid (500 mg QID) for 28 days. Lesions in nine of these patients were healed at the time of the 1.5 month followup (41% healing rate).

It is clear that a low self-healing rate in South American cutaneous leishmaniasis can not be assumed, and that studies on potentially new therapeutic regimens will require observations on untreated patients with similar lesions. The wide range of clinical response after 1–2 weeks of treatment or observation, with lesions that ultimately heal, has not been previously unreported, and should be valuable information for clinicians who manage individual cases. The results of this and other reports on the use of allopurinol and its ribonucleoside in the treatment of leishmaniasis are critically reviewed.

Multidrug-resistance (MDR) in neoplastic cells is frequently characterized by the overexpression of P-glycoprotein (PGP), a 170 kDa transmembrane glycoprotein that binds multiple cytotoxic drugs as well as calcium channel antagonists. Chloroquine resistance in Plasmodium falciparum appears to be analogous to MDR in neoplastic cells, where the induction of resistance with one drug confers resistance to other structurally and functionally unrelated drugs. To test the hypothesis that chloroquine resistance in P. falciparum and antimony resistance in Leishmania is mediated by a similar mechanism of MDR in mammalian neoplastic cells, a PGP-specific monoclonal antibody (C219) was used to determine the presence of PGP genes in resistant and sensitive Plasmodium and Leishmania parasites by indirect immunofluorescence assays and Western blotting procedures. These PGP-like components were detected in both drug-sensitive and -resistant Plasmodium and Leishmania cells. A 40–42 kDa component was observed to be greater in a chloroquine resistant P. berghei (C line) than in a chloroquine-susceptible P line. Differences observed between Pentostam-resistant and -sensitive Leishmania promastigote clones and isolates included the increased expression of 96–106 and 23–25 kDa peptides in drug-resistant L. enriettii, and increased amounts of two different peptides in two drug-resistant L. panamensis clones (i.e., 96–106 and 43–45 kDa in WR-746-CL4, and 53 and 23–25 kDa in WR-746-CL6). Interestingly, C219 detected a peptide of the same molecular weight (170 kDa) in amastigotes as in MDR KB carcinoma cells (KB-V1).

Comparative indirect immunofluorescent studies suggested that a correlation existed between the degree of antimony susceptibility and the concentration of the moiety recognized by C219 in two L. panamensis clones. Binding of the C219 monoclonal antibody to the PGP-like component of Leishmania was blocked by Pentostam, while the binding of C219 to multiple-drug resistant KB-V1 PGP was not inhibited by Pentostam, regardless of the PGP concentration. This suggests some degree of specificity in the binding of Pentostam to the Leishmania PGP-like components. In addition, these studies have demonstrated that drug-sensitive Leishmania accumulate two to five times more 125Sb-Pentostam than resistant clones.

Vaccination with SMW 68, an M, 68,000 glycoprotein of Schistosoma mansoni, induces significant protection in mice against challenge schistosome infection. This resistance occurs without the use of adjuvants and without sensitizing animals to granuloma formation. Likewise, passive transfer of monoclonal antibody (MAb) 31-3B6 against SMW 68 confers partial protection against challenge infection. As a first step in understanding how the immune response to this molecule leads to resistance, SMW 68 was localized in three developmental stages of the parasite by immunoelectron microscopy using MAb 31-3B6 and polyclonal antisera raised against purified SMW 68. In cercariae and schistosomula, MAb 31-3B6 bound electron-dense granules within the head gland and similar granules in the preacetabular glands. In adult worms, SMW 68 or related antigens were found to be widely distributed in tissues. Binding of specific antisera was most pronounced in the gut and tegument of male worms, but less so in subtegumental muscles. We conclude that SMW 68 is presented to the immune system in various ways during parasite development. The protective protein or epitope is excreted, and presented on the surface and in the cytoplasm at various stages of the life cycle. The relationship of the location of this protein to its role in protective immunity is discussed.

A cDNA that encodes Schistosoma mansoni tropomyosin, except for 10 amino acids at the amino terminus, has been cloned into a pOTSNCO plasmid vector. Induced expression resulted in a constant level of recombinant protein production. The recombinant S. mansoni tropomyosin was purified from preparative SDS-PAGE gel and by a combination of 20% ammonium sulfate fractionation and fast protein liquid chromatographyionexchange chromatography. The purified recombinant S. mansoni tropomyosin was tested as an immunodiagnostic reagent in Western blot and enzyme-linked immunosorbent assays. Sera from individual patients with chronic S. mansoni infection, but not S. haematobium, S. japonicum, parasitic infections other than schistosomiasis, and without infection reacted with the recombinant tropomyosin. The species specificity of S. mansoni tropomyosin suggests that further study of its potential as an immunodiagnostic reagent is warranted.

Adult Onchocerca volvulus worms, extracted from nodules of Guatemalans by collagenase digestion, were examined whole and by histological techniques. One group of persons received a single 150 µg/kg dose of ivermection; two other groups (one with older and one with younger nodules) received four similar doses of ivermectin at 6-month intervals. For each group, there were comparable untreated controls. All nodules were removed six months after the last dose. After a single dose, the only significant difference from the controls was in the decreased proportion of female worms producing live microfilariae. After four doses, there were significant increases in the proportions of moribund/dead female worms and of live uninseminated females, when compared with the corresponding controls. There were also fewer male worms present, but this difference was not significant. Six months after the conclusion of the 4-dose regimen, the proportion of female worms producing live microfilariae was significantly lower than in the groups that had received a single dose.

Peripheral blood mononuclear cells (PBMC) from acute leptospirosis patients with and without acute renal failure were studied in order to investigate the status of cellular immunity in this disease. We analyzed the lymphocyte subsets of leptospirosis patients by immunofluorescence and their responsiveness to the mitogens phytohemagglutinin (PHA) and pokeweed mitogen (PWM). Additionally, we investigated the effect of the patients' sera on normal PBMC proliferative response.

We observed a decrease in the CD3+ and CD4+ cell subsets in patients with and without acute renal failure, or in percentage values alone in those who had recovered from renal failure. An increase in the number of B lymphocytes was observed in all patients, compared with controls. This increase in B lymphocytes was seen even in patients who had recovered from renal failure, when the number of CD3+ and CD4+ lymphocytes had already returned to normal levels. The low PHA response observed only with lymphocytes for patients with acute renal failure suggests a suppressive effect. The proliferative response to PWM was comparable to controls, even in the patients with acute renal failure. This latter result and the expansion of the B cell number could be related to leptospiral-derived factor(s). We also showed that sera from patients with and without acute renal failure exerted some inhibitory activity on normal PBMC responses to PHA and PWM.

Although the redistribution of lymphocyte subsets and the serum suppressor activity were related to acute renal failure and leptospiral factor(s), we suggest that the cellular immune system was not irreversibly affected, which is compatible with the good prognosis seen in the patients studied.

The dissemination and replication of Dugbe (DUG) virus and its tissue tropisms in the tick vector Amblyomma variegatum were examined by immunohistochemical analysis using specific antibody, in situ hybridization with a viral-complementary riboprobe, and infectivity assays of dissected tissues. Dugbe virus was localized in both unfed and feeding adults inoculated as nymphs or orally infected by capillary feeding, and in nymphs infected by capillary feeding. In non-feeding ticks, the main sites of DUG virus replication were the epidermis, hemocytes associated with loose connective tissue, and a small number of phagocytic digestive cells in the gut lumen. Virus infectivity in the hemolymph was associated entirely with hemocytes. Dugbe viral antigen or infectivity was not detected in the salivary glands until after the start of feeding. Viral titers in the salivary glands of feeding ticks were about ten-fold higher than in gut, ovary, or loose connective tissue. The level of infection decreased during molting and increased during feeding. Viral particles and pathologic effects were not detected in infected ticks. The primary site of trans-stadial persistance of DuG virus is the hemocytes. Tick hemocytes and other motile cells may be important in the transmission of persistent virus infection from one cell or organ to another by diapedesis.