The American Journal of Tropical Medicine and Hygiene - Volume 65, Issue 5, 2001

The recombinant dengue virus type-4 vaccine candidate 2AA30 was attenuated in rhesus monkeys due to an engineered 30-nucleotide deletion in the 3'-untranslated region of the viral genome. A clinical trial to evaluate the safety and immunogenicity of a single dose of 2Adelta30 was conducted with 20 adult human volunteers. The vaccine candidate was well tolerated and did not cause systemic illness in any of the 20 volunteers. Viremia was detectable in 14 volunteers at a mean level of 1.6 log10 plaque-forming units/ml of serum, although all 20 volunteers seroconverted with a seven-fold or greater increase in serum neutralizing antibody titer on day 28 post-vaccination (mean titer = 1:580). A mild, asymptomatic, macular rash developed in 10 volunteers, and a transient elevation in the serum level of alanine aminotransferase was noted in five volunteers. The low level of reactogenicity and high degree of immunogenicity of this vaccine candidate warrant its further evaluation and its use to create chimeric vaccine viruses expressing the structural genes of dengue virus types 1, 2, and 3.

2Adelta30 is a live dengue-4 virus vaccine candidate with a 30-nucleotide deletion in its 3'-untranslated region. To assess the transmissibility of 2Adelta30 by mosquitoes, we compared its in vivo replication in mosquitoes with that of its wild type DEN-4 parent. Both the vaccine candidate and wild type virus were equally able to infect the mosquito Toxorhynchites splendens after intrathoracic inoculation. Relative to its wild type parent, 2Adelta30 was slightly restricted in its ability to infect the midgut of Aedes aegypti mosquitoes fed on an artificial blood meal and was even more restricted in its ability to disseminate from the midgut to the salivary glands. Thus, the 30-nucleotide deletion rendered the vaccine candidate more sensitive than its wild type parent to the mosquito midgut escape barrier. Most significantly, 2Adelta30 was not transmitted to 352 Ae. albopictus mosquitoes fed on 10 vaccinees, all of whom were infected with the vaccine candidate.

A dengue-2 (DEN-2) DNA vaccine coding for the premembrane and envelope (E) proteins and a recombinant fusion protein containing the B domain of the DEN-2 E protein fused to the maltose-binding protein (MBP) of Escherichia coli both elicited neutralizing antibody in mice. In order to achieve more rapid protective immunity as well as to increase the persistence of neutralizing antibody, we primed mice with the DNA vaccine (D), the recombinant MBP protein (R), or both (RD) given simultaneously, and then boosted twice with either the R (R/R/R or D/R/R) or D (D/D/D or R/D/D) constructs alone or the RD (RD/RD/RD) combination. All of the recombinant protein vaccines were given with alum as an adjuvant. The serum antibody response measured by enzyme-linked immunosorbent assay was highest in D/D/D mice and RD/RD/RD mice. The D/R/R mice showed an intermediate response, and the R/D/D and R/R/R showed the lowest response. The geometric mean (GM) 50% neutralizationtiter (50% plaque reduction neutralization, or PRNT50) was marginally higher for RD/RD/RD mice (891) at 9 months after priming than that for R/R/R mice (724). T he lowest GM PRNT50 titers were seen in the D/D/D mice (33) and R/D/D mice (40), and the D/R/R group had a slightly higher titer (156) than these 2 groups. The predominant antibody subclass for the D/D/D mice was immunoglobulin (Ig) G2a, similar to mice infected with live virus. The R/R/R mice showed an exclusive IgGI antibody response, and the RD/RD/RD response also was predominantly IgGI. The antibody subclass pattern of the R/D/D and D/R/R mice showed a more balanced distribution of both IgG1 and IgG2a. Investigating the neutralizing capacity of antibody subclasses suggested that both IgG1 and IgG2a could neutralize DEN-2 virus. Our observations indicate that the combination RD prime-boost regimen warrants further investigation as a vaccine strategy to prevent dengue infection.

The severity of dengue virus infection ranges from mild fever to dengue hemorrhagic fever and shock syndrome. The association of disease severity with virus replication in monocyte-derived macrophages (MDMs) was examined for dengue virus type 2 (DEN-2) isolates from Asia or America. Additionally, we constructed DEN-2 recombinant viruses with substitutions at residue 390 in the envelope glycoprotein (E390) because this residue is linked with the region of virus origin. Comparisons of virus yields of 3 isolates failed to show a correlation with clinical disease. However, the American strain did not replicate as well as the 2 Asian strains. For the recombinant viruses, substitution of Asn (Asian) at E390 with Asp (American) resulted in decreased ability to replicate in MDMs. These results are consistent with the proposal that the lack of association of native American DEN-2 strains with severe disease is linked to reduced ability to replicate in MDMs, and that Asp at E390 may contribute to this reduction.

The persistence of Trypanosoma cruzi in tissue and blood of 52 patients in the digestive form of chronic Chagas disease was studied. These patients had chagasic megaesophagus and underwent corrective surgery. Parasitologic (xenodiagnosis, hemoculture, or both), histopathologic (hematoxylin and eosin, and peroxidase-anti-peroxidase staining), and molecular (polymerase chain reaction [PCR] followed by slot-blot hybridization) tests were used in the analysis. The presence of T. cruzi, its genomic fragments, or its antigens could be detected in 98% (51 of 52) of the patients. The parasite was randomly identified in 76.9% of esophageal tissues and in 90.4% by PCR and in 73.1% by parasitologic methods from the blood. Fifty percent (26 of 52) of tissue samples had inflammation, 80.8% of which was associated with the parasite. Trypanosoma cruzi was also identified unassociated with inflammatory alterations. Higher tissue parasitism and intense inflammatory processes were observed in esophageal tissue from patients with Grade IV megaesophagus. These data demonstrate that in the digestive form of Chagas' disease, particularly in cases of megaesophagus, T. cruzi is frequently found, both in blood and tissues and may contribute to the pathogenic mechanisms involved.

Infection with the helminth parasite Schistosoma mansoni is associated with a pathogenic granulomatous response to parasite eggs. Multiple cell types constitute the granuloma with eosinophils achieving numerical dominance. We hypothesize that eosinophil dominance is achieved by selective apoptosis in lymphocytes. We report here that lymphocytes from both the spleens and granulomas of S. mansoni-infected mice undergo apoptosis. We also show that granuloma lymphocytes are more susceptible to Fas-FasL-mediated apoptosis than spleen lymphocytes and this apoptosis may be related to antigen concentration. Conversely, eosinophils from the granuloma and spleens of S. mansoni-infected mice are resistant to apoptosis in vivo and are protected in vitro from Fas-FasL-mediated apoptosis by the absence of FasL expression in the presence of Fas expression. Finally, the apoptotic regulatory molecules Bcl-2, Bcl-xL, and Bax, do not appear to play a significant role in the regulation of eosinophil apoptosis in the schistosome granuloma.

In vitro drug susceptibility profiles were assessed in 75 Plasmodium falciparum isolates from 4 sites in Myanmar. Except at Mawlamyine, the site closest to the Thai border, prevalence and degree of resistance to mefloquine were lower among the Myanmar isolates as compared with those from Thailand. Geometric mean concentration that inhibits 50% (IC50) and 90% (IC90) of Mawlamyine isolates were 51 nM (95% confidence interval [CI], 40-65) and 124 nM (95% CI, 104-149), respectively. At the nearest Thai site, Maesod, known for high-level multidrug resistance, the corresponding values for mefloquine IC50 and IC90 were 92 nM (95% CI, 71-121) and 172 nM (95% CI, 140-211). Mefloquine susceptibility of P. falciparum in Myanmar, except for Mawlamyine, was consistent with clinical-parasitological efficacy in semi-immune people. High sensitivity to artemisinin compounds was observed in this geographical region. The data suggest that highly mefloquine-resistant P. falciparum is concentrated in a part of the Thai-Myanmar border region.

We conducted a quasi-experimental study to compare the response to meglumine antimoniate in patients with localized cutaneous leishmaniasis from two endemic areas of Brazil that were infected by two Leishmania species. Sixty-one were infected by Leishmania (Viannia) braziliensis (group B) and 57 by L. (V.) guyanensis (group G). All had a parasitologically proven diagnosis and were treated with 20 mg of pentavalent antimonial (SbV)/kg/day given intravenously or intramuscularly for 20 days. Main outcomes were diagnosed using clinical criteria three months after treatment and patients were followed for six months. Intention-to-treat analysis showed a higher failure rate in group G (relative risk [RR] = 1.5, 95% confidence interval [CI] = 1.1-2.0, chi2 = 7.44, P = 0.006). The analysis using an explanatory approach including 52 patients from group B and 49 from group G, who were regularly treated and followed for six months, showed a low cure rate (50.8% in group B and 26.3% in group G) with a greater risk of failure in the latter group (RR = 1.7, 95% CI = 1.2-2.5, chi2 = 8.56, P = 0.003). The effect of the etiologic agent remained significant after adjusting for age, disease duration, and site and number of lesions that were identified as predictors of failure in a logistic regression model. We concluded that Leishmania species constitute an important factor in predicting the outcome of cutaneous leishmaniasis treated with a pentavalent antimonial.

A double-blind, randomized trial was undertaken in Guatemala to determine the therapeutic efficacy of an ointment for the treatment of cutaneous leishmaniasis that contained 15% paromomycin and 12% methylbenzethonium chloride and that was applied twice a day for 20 days. The treatment group included 35 patients, and the placebo group included 33 patients. The initial clinical response rate (13 weeks after completing the treatment) was 91.4% in the treatment group and 39.4% in the placebo group. The final clinical response rate at the 12-month follow-up examination was 85.7% (31 of 35) in the treatment group and 39.4% (13 of 33) in the placebo group (P < or = 0.001). In general, the treatment was well tolerated and was never interrupted because of adverse effects. The number of adverse effects reported in the placebo group was lower than in the treatment group (16 events versus 30 events). All adverse effects reported by patients disappeared within 1 week of completing the treatment. Our findings show that the combination of paromomycin with methylbenzethonium chloride for 20 days is a good alternative for antimonial treatments of cutaneous leishmaniasis in Guatemala.

This study evaluated the cure rate of the standard recommended regimen for Plasmodium vivax malaria in Brazil and assessed risk factors for failures. Fifty patients with vivax malaria given supervised medical treatment (standard dose of chloroquine: total dose = 1.5 g over a three-day period plus primaquine: total dose = 210 mg over a 14-day period) were followed for six months in a non-endemic area. Cox's regression was used to identify predictors of relapses. Among the 289 patient-months of follow-up, seven relapses were identified (2.4 relapses per 100 person-months) between 33 and 137 days after treatment initiation. Risk factors for relapses (P < or = 0.05) were female sex, higher parasitemia at baseline, shorter number of days with symptoms prior to baseline, and lower mg/kg dose of primaquine. Relapses following supervised vivax treatment is in principle a necessary, but not sufficient, component of in vivo parasite resistance. Results indicate that other factors, principally sub-therapeutic primaquine doses, may explain the occurrence of vivax treatment failures.

An in vivo drug sensitivity study was conducted in Magoda village in northeastern Tanzania to evaluate the usefulness of polymerase chain reaction (PCR)-based genotyping of Plasmodium falciparum parasites to distinguish between re-infection and treatment failure. The study tested P. falciparum susceptibility to a combination of sulfadoxine/pyrimethamine (Fansidar; F. Hoffmann La Roche, Basel, Switzerland). Blood samples were collected before treatment and on days 7, 14, or 28 post-treatment in 51 asymptomatic children, of which 26 could not clear parasitemia within seven days post-treatment. Among the remaining 25 children who had no detectable parasites on day 7, only five remained parasite negative up to day 28. Primary and recrudescent P. falciparum parasites were analyzed by PCR using family specific primers for merozoite surface protein-1 (MSP-1), MSP-2, and glutamate-rich protein (GLURP). All samples contained multiple P. falciparum infections. For all children with recrudescent P. falciparum, common alleles were detected in both the primary and recrudescent samples. However, in no child were the exact same alleles detected in both samples, indicating that probably at least some of the recrudescing parasites originated from new infections. The study demonstrates the general usefulness of PCR genotyping technique in distinguishing re-infections from true recrudescences following therapeutic drug treatment.

The data for this analysis are based on the schistosomiasis control project of the Noguchi Memorial Institute for Medical Research, University of Ghana, Legon, Ghana, designed to study the feasibility and effectiveness of an integrated schistosomiasis control program. It embraced chemotherapy and health education for community motivation. The study was carried out from 1993 to 1997. This paper presents observations made 24 months after intervention. Eight communities in southern Ghana were grouped into three areas. Individuals in all the areas received praziquantel after the baseline data collection in 1992-1993. Area 1 had passive while Area 3 received active health education. Area 2 received no education. Prevalence of schistosomiasis was the response variable of interest while age, sex, and area were considered as possible influencing variables. The model for the baseline data indicated no significant difference in prevalence among the three areas. The model 24 months after intervention indicated a significant difference among the three areas, suggesting a possible influence of the health education that motivated community participation in the provision of facilities for the control of schistosomiasis.

Starch gel electrophoresis was used to assess the polymorphism of 7 isoenzymes in single mosquitoes (field-collected F0 or F1 generation) for Aedes albopictus (8 strains) from northern Madagascar. Mosquitoes of the F2 generation (3 strains of Aedes aegypti and 10 strains of Ae. albopictus) were tested for oral susceptibility to dengue type 2 virus. Aedes aegypti was less susceptible to viral infection than Ae. albopictus. The genetic differentiation was less high between Ae. albopictus populations collected in agglomerations connected by highly frequented roads, indicating that human ground transportation favors mosquito dispersal. These results have implications for the ecology, pattern of migration, and relative importance in epidemic transmission of dengue viruses between the 2 Aedes species.

A population from the Wuchereria bancrofti-endemic island of Mauke was reevaluated retrospectively by use of the Og4C3 circulating antigen (CAg) enzyme-linked immunosorbent assay to assess active infection in relation to host responses by age and gender. Use of microfilaremia (Mf) alone misclassified approximately 50% of infected people, although CAg and Mf levels were positively correlated. Levels of CAg peaked between those aged 31-60 years; men aged > 60 years had a significantly higher CAg prevalence (> 90%) than women. Filaria-specific immunoglobulin (Ig) G4 reached maximum levels in both genders at age 51-60 years. By analysis of variance, both age and gender significantly influenced CAg and IgG4, with men having higher levels of both in the total population. Individuals positive for CAg had significantly lower lymphocyte proliferation responses to parasite antigen than did CAg-negative people, regardless of clinical status. This study reemphasizes the importance of CAg measurements for accurately assessing filarial prevalence and clinical status and demonstrates the relationship between active infection and immune responsiveness.

Regional differences in immune responsiveness have been studied by comparing the frequency of cytokine producing T cells in healthy African children and adults and their age-matched European counterparts. By use of flow cytometry for the intracellular detection of cytokines an overall expansion of CD4+ and CD8+ T cells producing the Type 1 cytokines interleukin (IL)-2 and interferon (IFN)-gamma was observed in adults when compared with children, giving credit to the cumulative effect of contacts with environmental antigens. The CD4+ cells expressing the Type 2 cytokines IL-4 and IL-13, however, increased only in Africans, probably reflecting continuously present challenges with antigens that preferentially drive Type 2 responses. A striking increased frequency of both Type 1 and Type 2 cytokines producing T cells was found in African adults when compared with their European counterparts. The quantitative and qualitative regional differences in immune reactivity are likely to be of significance for all immune intervention strategies, especially for the design of vaccines.

Brazil is the only country endemic for zoonotic visceral leishmaniasis (ZVL) that regularly conducts epidemiologic and prophylactic control programs that involve the treatment of human cases, insect vector control, and the removal of seropositive infected dogs. This report reviews 60 studies reporting data on the efficacy of these recommended control tools and concludes that in Brazil 1) eradication of the disease in Minas Gerais was achieved by the concomitant use of the three control methods, 2) although seropositivity by an immunofluorescent assay is not completely related to infectiousness, the removal of seropositive dogs leads to a significant reduction of canine and human incidence, 3) improvement of the sensitivity of the diagnostic tool used for canine control should optimize the efficacy of control, and 4) although difficult and expensive, the public health dog control campaigns performed in Brazil reduced the incidence of ZVL and should be maintained since treatment of dogs is an unrealistic intervention, both because of its prohibitive cost and relatively poor effectiveness.

The prevalence of Cryptosporidium parvum infection and its seasonality were studied in a small rural village occupied predominantly by aged people in Hwasun-gun, Chollanam-do, Republic of Korea. Fecal samples were collected monthly from November 1996 to October 1997 and examined for enteric parasites. To detect oocysts of C. parvum, the modified acid-fast stain was applied. To determine effects of climatic factors, local weather reports were collected. The overall oocyst prevalence during 1 year was 57.0% (77 of 135), and was significantly higher (P < 0.0001) in aged people--those aged 50-59 years (80.0%) and those aged 60-69 years (69.0%)--than in younger groups. No significant difference (P > 0.05) was noted between men and boys (53.6%) and women and girls (59.5%), but significant (P < 0.05) household clustering was recognized. People aged > 50 years tended to be more repeatedly positive than people in the younger group. The rate varied monthly from 7.8 to 20.0% (average, 12.6%), with significantly higher (P < 0.05) rates in spring than in summer and winter months. This seasonality had little relation with temperature (r = 0.04), but a weak correlation was found with rainfall (r = 0.4). It is of special interest that cryptosporidiosis is highly endemic among the aged population.

A widespread reduction in Plasmodium falciparum gametocyte prevalence could reduce malaria transmission. After infection with P. falciparum, a variable proportion of people are found to be gametocytemic. We analyzed risk factors associated with gametocytemia at presentation and 7 days later. We enrolled 1,198 children in 2 antimalarial drug trials between September and December 1998. The children were assigned to 1 of 4 treatment groups: chloroquine only; pyrimethamine-sulfadoxine (PSD) only; PSD combined with 1 dose of artesunate; and PSD combined with 3 doses of artesunate. By the time of enrollment, 200 (17%) of 1,198 children were gametocyte carriers. Three independent risk factors were associated with gametocytemia at enrollment. Children with anemia were more likely to carry gametocytes, whereas children with fever (> 37.4 degrees C) or high parasite densities (> 100,000 parasites/microL) were less frequently gametocyte carriers. Children with at least 2 of the risk factors were 4 times more likely to be gametocytemic than children with < 2 risk factors (odds ratio [OR], 4.4; 95% confidence interval [CI], 2.7-7.1). Seven days after the start of treatment, 355 (37%) of 466 assessable children were found to be gametocyte carriers. Children treated with PSD alone had a significantly higher risk of being gametocytemic by Day 7 compared with children in the other 3 treatment groups. In the subgroup of children who had no detectable gametocytes on enrollment, the effect of treatment with PSD + 3 doses of artesunate was most marked. Nineteen (10%) of 198 children treated with PSD + 3 doses of artesunate became gametocytemic, in contrast to 184 (57%) of 321 children treated with PSD alone (OR, 12.7; 95% CI, 7.3-22.1). Early treatment with highly effective antimalarial therapy has the greatest chance of preventing gametocytemia. The choice of a first-line antimalarial drug for uncomplicated malaria should not only take into consideration the ablation asexual parasitemia but also the suppression of gametocytemia.