The American Journal of Tropical Medicine and Hygiene - Volume 56, Issue 5, 1997

The role of Trypanosoma cruzi in the pathogenesis of myocarditis in the chronic phase of Chagas' disease is still controversial, with autoimmune mechanisms frequently being proposed. In the present work, we demonstrate that higher numbers of CD8+ T cells are correlated with the presence of parasite antigens, suggesting an important role for the parasite in the development of myocardial inflammation. Quantification of the mean numbers of CD8+ and CD4+ T cells per 400× microscopic field was performed in myocardial specimens from 33 chronic chagasic patients with heart failures (nine biopsies and 24 necropsies), using an immunoperoxidase technique. The cases were grouped according to a semiquantitative score of the relative amounts of T. cruzi antigens: group 1 = absent (14 cases); group 2 = scarce extracellular or intramacrophagic antigens (12 cases); group 3 = many extracellular or intramacrophagic antigens plus T. cruzi intramyocytic pseudocysts (seven cases). The mean numbers of CD8+ and CD4+ T cells in groups 1, 2, and 3 were 6.94 and 3.79, 13.89 and 6.24, and 17.91 and 5.97, respectively. The numbers of CD8+ T cells in groups 2 and 3 were significantly higher compared with group 1 (no T. cruzi antigens), but were not different from each other. Scarce, extramyocytic T. cruzi antigens were associated with an intense inflammatory infiltrate, suggesting that a delayed-type hypersensitivity immune mechanism is induced by the parasite; intact myocardiocytes containing parasites did not show an inflammatory reaction around them. A poor inflammatory response was frequently associated with many extramyocytic antigens and myocardial parasite pseudocysts, suggesting that active proliferation and dissemination of the parasites occur when the immunologic response is diminished. The number of CD4+ T cells did not vary significantly among the three groups. We conclude that the CD8+ T cell is the main cell type responsible for immune activation in chronic, human, chagasic myocarditis and is probably activated by the presence of T. cruzi antigens associated with internal myocytic host antigens. The absence of a significant member of CD4+ T cells in the presence of T. cruzi antigens suggests inhibition of CD4+ T cell activation or the lack of a class II major histocompatibility complex molecule presentation mechanism.

This study was undertaken to correlate the clinical features and pathologic changes noted during the initial and later stages of fatal typhoid illness. Five cases who died during the initial stage of the illness (< 2 weeks from onset) had altered mental status, tachypnea, and tachycardia. Three had shock and elevation of serum creatinine values. Autopsies of all five revealed hyperplastic Peyer's patches, features of adult respiratory distress syndrome, and megakaryocytosis. Five other cases died during the later stage of the illness (≥ 2 weeks after onset). They had a left shift in peripheral blood leukocyte count. Autopsies revealed deep ileal ulcerations with or without perforation and peritonitis and intercurrent pneumonia. Three of them had disseminated intravascular coagulation. Further studies are warranted to understand the mediators of shock and tissue injuries during the initial period of the illness.

Antimalarial drugs can affect the heart and trigger life-threatening arrhythmias. However, little is known about the frequency with which cardiac abnormalities occur during uncomplicated attacks of malaria. Therefore, we have studied the electrocardiograms of 139 Gambian children with uncomplicated falciparum malaria who were treated with co-artemether, pyrimethamine/sulfadoxine, or chloroquine. The QTc intervals were measured on presentation, and four and eight days after treatment. No significant differences in mean QTc or heart rate were found between children in the three treatment groups on days 0, 4, or 8. After adjustment for the type of antimalarial therapy in an analysis of variance, the mean (SD) QTc intervals on days 0, 4, and 8 were 402 (22.6), 416 (23.1), and 405 (24.3) msec, respectively. The mean QTc on day 4 was significantly longer than the mean QTc on days 0 or 8 (P < 0.01 in both cases). A quadratic line was fitted for QTc against time for each antimalarial therapy. No significant differences were found between the quadratic lines of the three groups. A weak association was found between QTc and the degree of parasitemia (r = 0.17, P = 0.04) and temperature (r = -0.23, P = 0.01) measured on day 0. The QTcs were measured in 18 children who experienced a second episode of malaria. The changes in QTc observed during second episodes were similar to those observed during the first attack. Changes in QTc in five children who developed severe malaria were similar to those found in the remaining children who did not develop severe malaria. This study indicates that the QTc interval changes during the early phase of malaria and this change is independent of the type of antimalarial therapy given.

The objective of this study was to examine the disposition of proguanil in malaria-infected Thai patients with acute uncomplicated falciparum malaria. Eleven patients were administered 500 mg of proguanil twice a day for three days (total dose = 3,000 mg). Four patients were tentatively classified as extensive metabolizers (EMs) and seven as poor metabolizers (PMs). The mean plasma clearances of proguanil for EMs and PMs were 1.31 and 1.10 L/hr/kg, respectively. The mean elimination half-life of proguanil was statistically longer in PMs than EMs (19.6 hr versus 16.1 hr; P = 0.01). Plasma clearance and elimination half-life of proguanil in the malaria patients were comparable with those reported in the literature for healthy Thai volunteers. In contrast to other ethnic groups, Thai EM patients had relatively low plasma concentrations of cycloguanil, the active metabolite of proguanil. None of the 11 patients treated with proguanil were cured of malaria and their phenotypic status did not affect the treatment outcome. Although high levels of parasite resistance to cycloguanil were probably responsible for the poor response to proguanil treatment, the inability of Thai EM and PM patients to produce cycloguanil may have also contributed to the treatment outcome.

The pharmacokinetics of artemisinin was studied in 11 Vietnamese patients with uncomplicated falciparum malaria after a single 500 mg oral dose. Curative treatment with mefloquine (15 mg/kg) was provided 24 hr after the artemisinin dose. Artemisinin concentrations were measured by high-performance liquid chromatography with electrochemical detection. The following pharmacokinetic results were found (all mean ± SD): calculated volume of distribution/bioavailability = 22.8 ± 16.6 L.kg-1, mean absorption time = 1.16 ± 0.92 hr, calculated maximum concentration = 364 ± 250 µg.L-1 occurring at 2.88 ± 1.71 hr after drug intake, and an elimination half-life of 2.72 ± 1.76 hr. Bioavailability was low. These results do not differ from results in healthy subjects. Parasites disappeared rapidly, with a mean parasite clearance time of 36 hr. No relationship was found between pharmacokinetics and the parasite elimination rate. Tolerance to the single dose of artemisinin was good. No adverse effects were detected. In conclusion, pharmacokinetics of a single dose of artemisinin for uncomplicated falciparum malaria is not different from findings in healthy subjects. A single dose of 500 mg of artemisinin is effective in reducing parasitemia in nonsevere falciparum malaria and is well-tolerated.

The compound WR 238605 is a primaquine analog being developed by the U.S. Army as an antimalarial drug. Currently, there is no established treatment for Plasmodium vivax parasitemias that are not cured by chloroquine. This study tested WR 238605, chloroquine, and their combinations against a chloroquine-resistant strain of P. vivax (AMRU 1) in Aotus monkeys. A total dose of 3 mg/kg of WR 238605 given at a dosage of 1 mg/kg/day for three days cleared patent parasites in all eight monkeys but recrudescence of parasitemia occurred 15–25 days after initiation of treatment. A total dose of 9 mg/kg of WR 238605 over a three-day period cured all three monkeys of their infections. A total dose of 30 mg/kg of chloroquine did not clear patent infections in three monkeys, whereas a total dose of 60 mg/kg generally (two of three) cleared patent parasitemia but did not cure. Whereas total doses of 30 mg/kg of chloroquine or 3 mg/kg of WR 238605 given alone failed to cure, both drugs given in combination at these dosages cured two of three infections. These results indicate that WR 238605 may be an alternative treatment for chloroquine-resistant vivax malaria.

A therapeutic trial, involving 130 Schistosoma mansoni—infected children, with no previous history of antischistosomal treatment, was carried out to evaluate the efficacy of two different dose regimens of praziquantel. The study was carried out because low cure rates were described in this recently established (1990) S. mansoni focus in northern Senegal, following treatment with a standard dosage of 40 mg/kg. The subjects were randomly allocated into two groups: one group (1) received 40 mg/kg in one oral dose, the other group (2) was treated with two oral doses of 30 mg/kg at a 6-hr interval. Parasitologic examination and circulating anodic antigen (CAA) detection were performed before, 10 days, three, six, and 21 weeks after chemotherapy. No significant differences in cure rates were found between the two groups. Six weeks after treatment, 34% and 44% of the individuals were found to be stool negative in group 1 and group 2, respectively. However, only 10–15% became completely negative according to the serum CAA antigen assay. Mean egg counts were reduced by 99% in both groups. Antigen detection confirmed the parasitologic results. Fewer side effects were observed in the group treated with 2 × 30 mg/kg, which may be explained by split dosage administration. Our study shows that the low cure rates observed in this area could not be improved by using a higher dosage of praziquantel.

Persons employed as vehicle washers in the town of Kisumu, Kenya are exposed for several hours each day to water in Lake Victoria that contains Schistosoma mansoni—infected Biomphalaria pheifferi snails. This results in a focus of high endemicity for schistosomiasis and these persons have very high concentrations of eggs in their feces (mean ± SD = 1,469 ± 1,581 eggs per gram [EPG] of feces). Fecal egg counts, but not circulating cathodic antigen (CCA) levels, in these schistosomiasis patients differed strikingly based on the patient's seropositivity for human immunodeficiency virus (HIV). Patients who were infected with S. mansoni and were seropositive for HIV had similar levels of CCA but excreted fewer eggs (643 ± 622 EPG; n = 16) than individuals who were not seropositive for HIV infection (1,891 ± 1,779 EPG; n = 37) (P = 0.009). Egg excretion ratios (EPG/CCA) of the seronegative group were also significantly higher than those of the seropositive group. Those in the seropositive group showed a significant correlative relationship between egg excretion ratios and CD4+ lymphocyte percentages. These observations are compatible with the hypothesis that schistosome eggs exit the human host through the requisite facilitation of functional immune responses, and that the efficacy of this process decreases in schistosomiasis patients co-infected with HIV as their peripheral blood CD4+ cell levels decrease.

Sera from 61 Indian patients with visceral leishmaniasis caused by infection with Leishmania donovani were tested for the presence of T helper 1 (Th1) cell-(interferon-γ [IFN-γ]) and Th2 cell-associated cytokines (interleukin-4 [IL-4] and IL-10). The IFN-γ activity was detected in 53%, IL-4 in 84%, and IL-10 in 56% of patient samples. Sera from 10 healthy Indian controls showed detectable IFN-γ in 90%, IL-4 in 10%, and IL-10 in 20%; corresponding percentages for sera from eight healthy American controls were 100%, 12%, and 0%, respectively. Quantitative data for the 61 patients compared with the 10 Indian controls indicated comparable mean levels of IFN-γ, but three- and 13-fold increases in IL-10 and IL-4, respectively. Undetectable IFN-γ activity, observed in 47% of patients, was associated with the presence IL-4 alone or in combination with IL-10 but not with IL-10 alone. In patients who had failed prior therapy (n = 29) compared with previously untreated patients (n = 32), IFN-γ levels were 67% lower and IL-4 levels were two-fold higher; IL-10 activity was comparable. These results using peripheral blood support the presence of a suppressive Th2 cell-associated immune response in symptomatic Indian kala-azar and point to a possible role for IL-4.

In preparation for a recently reported, independent field trial of SPf66 malaria vaccine efficacy in Thailand, we first established the safety and immunogenicity of two clinical lots of U.S. manufactured lots of SPf66 in a series of overlapping Phase I studies. The vaccine was produced in approved laboratories using good manufacturing practices. Two clinical lots of alum-adsorbed SPf66 were evaluated in a combined, open-label, Phase I clinical trial involving 50 healthy, malaria-experienced Karen adults and children. Volunteers were grouped by age and immunized sequentially. Group 1 had 30 adults, Group 2 had 10 children 8–15 years of age, and Group 3 had 10 children 2–6 years of age. The SPf66 vaccine was well tolerated in this malaria-experienced population. The most common side effects were erythema, induration, warmth, and tenderness at the site of injection, which typically resolved within 24–48 hr. One adult volunteer developed an acute urticarial rash following the third dose. Among adults, and to a lesser extent older children, females had more local reactions than their male counterparts. Seroconversion to SPf66 by enzyme-linked immunosorbent assay occurred in 76% of volunteers receiving two or three doses. This vaccine was safe and immunogenic in malaria-experienced Karen adults and children. This study establishes the comparability of U.S.-manufactured SPf66 with that of Colombian origin, and is important for interpreting the efficacy results of U.S.-manufactured SPf66 in the same study population.

A live oral cholera vaccine should ideally protect against both classical and El Tor biotypes of Vibrio cholerae O1. An El Tor biotype vaccine strain, therefore, would complement classical cholera vaccine strain CVD 103-HgR, a strain already in use in some countries. In this study, 25 healthy adult volunteers received a single dose of 108 colony-forming units of El Tor vaccine strain CVD 111, a derivative of El Tor Ogawa strain N16117 deleted in the virulence cassette. Three (12%) volunteers developed mild diarrhea (mean stool volume = 813 ml) but no systemic symptoms; 23 (92%) of the 25 volunteers developed serum vibriocidal antibodies (geometric mean titer = 1: 2,291). Five weeks after vaccination, 18 vaccinees and eight unimmunized control volunteers underwent wild-type challenge with El Tor Ogawa strain 3008. Three (16.7%) of 18 vaccinees and seven (87.5%) of eight controls developed diarrhea (P = 0.001) (vaccine efficacy = 80.9%). Further studies are underway to determine a dosage of CVD 111 that will be more clinically acceptable but equally immunogenic and protective.

Plasmodium falciparum is the major cause of malaria morbidity and mortality in the world. Biologic and antigenic diversity is a characteristic of this parasite and infections can consist of several genetically diverse parasites. The daily dynamics of these parasite subpopulations were investigated in asymptomatic children in rural Tanzania. Fingerprick blood samples were collected on 14 consecutive days from 20 children. Parasite densities were detected by light microscopy and genotyping of P. falciparum was done using a nested polymerase chain reaction (PCR) assay targeting polymorphic regions on the merozoite surface protein-1 (MSP-1), MSP-2, and glutamine-rich protein (GLURP) genes. In the eight children harboring P. falciparum throughout the study period, infections were found to be highly complex with daily changes in both parasite density and genotypic pattern. A nonrandom, 48-hr periodicity in these fluctuations suggests that P. falciparum infections consist of inherently synchronous subpopulations of parasites. These findings have important biologic and epidemiologic implications since one blood sample may only partly reflect the whole parasite population in an infected individual.

Specific rodent species are principal hosts for each of the well-characterized members of the virus family Arenaviridae. Guanarito virus (Arenaviridae) is the etiologic agent of Venezuelan hemorrhagic fever. A previous study on the epidemiology of Venezuelan hemorrhagic fever revealed extensive arenavirus infection (presumed to be caused by Guanarito virus) in two rodent species, Sigmodon alstoni and Zygodontomys brevicauda, collected from the region of Venezuela in which the disease is endemic. In the present study, four arenavirus isolates recovered from the Municipality of Guanarito (two isolates each from S. alstoni and Z. brevicauda) were characterized to learn more about the natural rodent host relationships of Guanarito virus. Serologic tests and analyses of nucleocapsid protein gene sequence data indicated that the two isolates from Z. brevicauda are strains of Guanarito virus and that the two isolates from S. alstoni are representatives of a novel New World arenavirus (proposed name Pirital) that is antigenically and phylogenetically distinct from all known New World arenaviruses. The results of the present study provide further evidence that the cane mouse Z. brevicauda is a natural host of Guanarito virus and suggest that the cotton rat S. alstoni is the natural reservoir host of Pirital but not Guanarito virus.

Due to the lack of an animal model, previous studies of sandfly fever have relied upon human challenge trials. We examined the infectivity and potential pathogenicity of sandfly fever virus in cynomolgus monkeys (Macaca fascicularis). Three different preparations of sandfly fever virus, Sicilian strain, and a placebo were compared by different routes of administration. The most notable postchallenge clinical event was a decrease in lymphocytes in the intramuscularly challenged monkeys. Plaque-reduction neutralization responses peaked earlier in animals challenged intravenously as compared with those in animals challenged intramuscularly. There was no evidence for neurotropism or meningeal inflammation. Sandfly fever virus was infectious for cynomolgus monkeys, but produced no detectable clinical disease that might serve as a marker for animal modeling studies. On the other hand, the preclinical data provide supportive evidence for safe parenteral administration of a Sicilian strain of sandfly fever virus inoculum to humans as a challenge model for sandfly fever disease.

An epidemiologic study was conducted to determine the prevalence of retroviral infections among people of Quechua origin in Cuzco and Quillabamba, Peru. The study volunteers included individuals at low and at high risk for retroviral infections. Each volunteer was interviewed to obtain clinical and epidemiologic data, and to identify risk behaviors for infection. The serum was tested for human immunodeficiency virus type 1 (HIV-1) and human T cell lymphotropic virus types 1/2 (HTLV-1/2) by standard enzyme-linked immunosorbent and Western blot assays. Among a total of 370 volunteers enrolled in the study, 276 were women and 94 were men whose ages ranged between 15 and 49 years. Infection with HTLV-1 was demonstrated in 5.1% (19 of 370), and one of these, a homosexual, was also positive for HIV-1; none had HTLV-2. Overall, the rate of HTLV-1 infection was 5.3% (5 of 94) for males and 5% (14 of 276) for females. Among the low risk group of 211 healthy pregnant women, five (2.3%) were positive for HTLV-1. The rate of HTLV-1 infection in this group was significantly correlated with a history of dental surgery, as well as other surgical procedures, and a history of jaundice. Among the volunteers who practiced risk behavior(s) for retroviral infections, the positive rates for HTLV-1 were 13.7% (7 of 51) for female sex workers, 6.2% (3 of 48) for homosexuals and/or bisexuals, 8.5% (4 of 47) for patients with sexually transmitted diseases (STDs), and 0.0% (0 of 13) for promiscuous heterosexual males. In female sex workers, HTLV-1 infection was found to be significantly associated with age, a history of STDs or genital ulcers, sexual intercourse during menses, and vaginal douching (P < 0.05). A low prevalence of HIV-1 infection indicates that the virus has not yet spread significantly in these areas.

Despite a growing body of evidence predominantly, but not exclusively, from Thailand suggesting that the risk of developing dengue shock syndrome (DSS) is greatest following an anamnestic dengue infection, particularly if the most recent infection was with dengue 2 virus, there continues to be debate about the justification for these claims. This report describes a five-year, prospective study in two townships (suburbs) in Yangon (Rangoon) Myanmar (Burma) in which attempts were made to confirm the data from an earlier prospective study in Thailand and to address some of the criticism of earlier studies. This investigation found the incidence of anamnestic dengue infections in DSS patients to be significantly higher than in the community from which they were drawn and a significantly higher risk of developing DSS following an anamnestic infection (particularly with dengue 2 virus) than following a primary infection with any serotype.

We report here two cases of Saudi patients who acquired chloroquine-resistant Plasmodium falciparum locally, without any history of foreign travel, blood transfusion, or drug abuse. Both were satisfactorily treated, the first with quinine and a pyrimethamine-sulfadoxine combination, and the other with quinine and tetracycline. These two cases suggest either the possible establishment of chloroquine-resistant P. falciparum in Saudi Arabia, or the beginning of the spread of resistant strains from countries with established resistance to this country. Diligent notification of cases by attending physicians to the Ministry of Health will help to achieve effective control.

To assess the effect of the Expanded Program on Immunization (EPI) in rural Africa, blood samples were collected in two Kenyan sublocations. Serum antibodies against tetanus toxoid were measured in 155 individuals 1–70 years of age. Titers greater than the protective level of 0.01 IU/ml were found in 47% of the population. Protection was significantly higher in children born after the launching of the EPI (68%) and in women who had been at childbearing age since then (69%). Significantly lower protection was demonstrated in other age and sex-groups. The level of protection in children was equal in the two populations, whereas protection in fertile women was significantly lower in the population living a long distance from a health center. Diphtheria anti-toxin was measured in the samples from one sublocation, and 70 of 84 individuals (83%) had antibody levels greater than the protective level. No age or sex difference could be found, and there was no correlation between response levels to diphtheria and tetanus. This implicates natural infections as an important source of diphtheria antibodies. Our findings demonstrate a need for better coverage of the adult population against tetanus. Furthermore, diphtheria transmission still appears to take place, underscoring the importance of diphtheria vaccination of travelers to rural Africa.

A study about the acceptability, protective efficacy, effectiveness, and cost of a repellent soap containing 20% diethyltoluamide and 0.5% permethrin was carried out on the Pacific coast of Ecuador and Peru, where malaria is endemic and the transmission is seasonal. The malaria vectors were Anopheles albimanus, An. punctimacula, and An. pseudopunctipennis in Ecuador and An. albimanus in Peru. Comparing the hourly mosquito bites on human subjects with and without the protection of the repellent soap, it showed that inactive, protected subjects were bitten 94.2% less than unprotected controls 2 hr after application of the soap. This protective efficacy was reduced to 81% after 6 hr. In persons physically active for 3 hr after application, the efficacy of the soap was 67% in the fourth hour after application and 52% in the sixth hour after application. Sweating decreased the protective efficacy of the soap even more. In a community-based malaria control program, the soap was introduced by community health promoters. Acceptance was good when it was given free of charge but reduced dramatically when it was sold. People used the soap mainly because of the nuisance of mosquitoes. The application was generally done correctly. However, no significant impact on the incidence of malaria episodes could be shown when comparing intervention communities with control communities, either in Ecuador, where the proportion of Plasmodium falciparum cases was high, or in Peru, where P. vivax was the only species of Plasmodium seen. This can probably be explained by the limited use of soap and the shift of mosquito bites from users to nonusers of the repellent soap. The cost of a soap program would be $4.60 (USA) per person per year, which seems to be quite high in terms of cost of soap and its distribution related to people's low cash income. The implications of the introduction of repellent soap into a control program are discussed.