The American Journal of Tropical Medicine and Hygiene - Volume 59, Issue 2, August 1998

An antigen-capture ELISA using monoclonal antibody (MAb) 128C3/3/21 was used to detect circulating parasite-derived antigens in the sera of patients actively infected with Schistosoma haematobium (31 males and four females, 5-25 years of age). The assay had a sensitivity of 100% (35 of 35 patients with antigen levels > 80 ng/ml) and a specificity > 99%. We used this ELISA to monitor antigenemia before treatment and one, three, and six months after treatment with a single oral dose of praziquantel (PZQ) (60 mg/kg in 20 patients or 40 mg/kg in 15 patients) and compared our findings with those indicated by other measures of disease progression. Circulating antigen levels decreased drastically after PZQ treatment (P < 0.001), with a significantly higher decrease occurring after treatment with 60 mg/kg than with 40 mg/kg. Although the mean antigen level was still significantly reduced (P < 0.001) at six months after treatment, 16 patients remained antigen-positive after six months, and nine had increased levels of antigenemia, reflecting reinfection in six patients and persistence of infection in another. We observed a correlation (r = 0.6, P < 0.01) between the level of circulating antigen and the intensity of infection as measured by egg count. We also found a direct relationship (P < 0.001) between antigen level and the severity of the disease as monitored by ultrasonography. We conclude that our ELISA may be a useful adjunct to other methods, such as ultrasonography, for monitoring the course of S. haematobium infection and treatment.

The DPA1 and DPB1 alleles of the major histocompatibility complex (MHC) class II were determined in 110 patients and 120 healthy controls of a Gabonese population from an area endemic for Schistosoma haematobium infection. The MHC-DP alleles of the variable second exons and their human leukocyte antigen (HLA) epitopes were correlated with egg excretion, interleukin-4 and interferon-gamma patterns, and bladder abnormalities, as detected by ultrasonography. A methionine at position 11 of the DP alpha molecule (Met-11) and DPA1*0301 were associated with schistosomiasis when compared with controls (phenotypic gene frequencies = 0.791 versus 0.583 and 0.555 versus 0.375, respectively). Met-11 homozygosity occurred more often in patients, whereas healthy controls were more frequently homozygous for an alanine at position 11 (Ala-11). The combination of the DPB1-epitope DEAV (positions 84-87 of the DP beta molecule) and Met-11 positive DPA1 alleles was more frequent in patients than in controls (0.573 versus 0.316). Two years after antischistosomal treatment, the rate of reinfection as examined in 55 of the 110 former patients was higher in DPA1*0301-positive individuals than in those not possessing this allele (P < 0.001). Ala-11 positive individuals showed less frequently ultrasonographic signs of bladder pathology than Ala-11 negative individuals (P < 0.05). Our results suggest a role of MHC-DP elements in the manifestation of disease in S. haematobium infection.

Praziquantel is the drug of choice for schistosomiasis chemotherapy. Although the exact mechanism of how praziquantel kills schistosomes remains poorly understood, the immune response of the host is an important factor in drug efficacy. It is thus possible that disease states of humans that lead to immunodeficiencies, such as infection with human immunodeficiency virus-1 (HIV-1), may render praziquantel less effective in treating schistosomiasis. To test this hypothesis, persons with high levels of Schistosoma mansoni infection who were or were not also infected with HIV-1 were treated with a standard regimen of praziquantel and monitored by quantitative fecal examination and plasma circulating cathodic antigen. Both groups responded to praziquantel therapy equally and individuals with low percentages (< 20%) of CD4+ T cells did not differ from individuals with higher CD4 cell percentages. These data demonstrate that persons with HIV-1 infection can be treated effectively for schistosomiasis with praziquantel.

Studies were conducted from 1986 through 1993 to further define the geographic distribution and relative importance of different species of Leishmania as a cause of leishmaniasis in Peru. Patients with a clinical diagnosis of cutaneous and/or mucosal or diffuse cutaneous leishmaniasis were enrolled at the Naval Medical Research Institute Detachment (NAMRID) Laboratory in Lima, the Tropical Disease Clinic at San Marcos University Daniel A. Carrión, the Central Military Hospital, and a Ministry of Health hospital in Cusco, Peru. Clinical features, lesion aspirates, and biopsy tissue were obtained from each patient. All specimens were collected and assayed separately, including multiple specimens from some of the same patients for Leishmania parasites by inoculating aliquots of either aspirates or biopsy tissue suspensions onto Senekji's blood agar medium. Stocks of Leishmania isolates were used to prepare promastigotes to produce extracts for identifying the Leishmania species by the cellulose acetate electrophoresis enzyme technique. A total of 351 isolates of Leishmania were obtained from 350 patients who were infected primarily in the low and high jungle of at least 15 different Departments of Peru. Of the 351 isolates, 79% were identified as L. (V.) braziliensis, 7% as L. (V.) guyanensis, 10% as L. (V.) peruviana, 2% as L. (V.) lainsoni, and 1.7% as L. (L.) amazonensis. The clinical form of disease varied depending on the species of Leishmania, with L. (V.) braziliensis being associated most frequently with cutaneous, mucosal ulcers and mixed cutaneous and mucosal disease, and L. (V) peruviana, L. (V.) guyanensis, L. (V.) lainsoni with cutaneous lesions. Leishmania (L.) amazonensis was isolated from six patients, three with cutaneous lesions, one with mucosal lesions, and two with diffuse cutaneous lesions. Among all of the leishmaniasis cases, males were affected more frequently, and cases occurred among patients less than 10 to more than 51 years of age. These data further defined the geographic distribution and the relative frequency of Leishmania species associated with different clinical forms of leishmaniasis in Peru.

Routine antenatal hepatitis B surface antigen (HBsAg) screening and immunization of risk babies is very effective in preventing perinatal transmission of hepatitis B virus (HBV). We studied 1,800 parturients attending a public hospital to assess the rationale for such vaccination in Bangladesh. In one in every 29 deliveries (63 of 1,800 or 3.5%), the mother was found to be HBsAg positive. All were asymptomatic and many (41 of 63 or 65%) without risk factors would remain undetected if HBsAg screening were performed on selected groups. Most of the HBsAg-positive mothers (54 of 63 or 85.7%) were found to be chronic carriers and 30.2% (19 of 63) were also hepatitis B e antigen (HBeAg) positive, indicating high infectivity. Although 23 cord blood were positive for HBsAg or HBeAg, none were positive for IgM antibody to hepatitis B core antigen (IgM anti-HBc), suggesting transplacental transmission of the antigens rather than intrauterine infection. These findings are discussed in relation to the cost-effectiveness of routine prenatal screening and immunization of risk babies compared with universal infant immunization.

In recent years, concerns have been raised regarding the safety of diethyltoluamide (DEET), one of the most widely used and reliable insect repellents available. This paper summarizes the recent evidence and concludes that concerns over safety appear largely unfounded.

Human intervention in the Brazilian Amazon region promotes contacts between humans and vectors that may favor the propagation of anopheline mosquitoes and the spread of malaria in the absence of planning and infrastructure to control this disease. Vector ecology studies were carried out to determine the risk areas. These data should help in designing appropriate malaria control measures. Data from 14 different regions are reported. Vectors are able to adapt to different environments, which made it necessary to study each area. The parameters studied were Anopheles breeding sites, species distribution, incidence, feeding preferences, hours of maximum activity of adult mosquitoes, seasonality, resting places, and the presence of Plasmodium. Species complexes were also studied. Anopheles darlingi may be responsible for maintaining malaria in human populations in this region. A reduction in the population density of A. darlingi in a particular geographic area can sometimes cause the disappearance of malaria. This species feeds at night but has a peak of activity at the beginning of the evening and another at dawn. Other species are mainly crepuscular and all anophelines demonstrated pronounced exophilia. The timing of feeding activities was found to vary in areas altered by human intervention and also depended on the time of the year and climatic conditions. The larvae were more abundant in the rivers with a less acidic pH and rural areas showed the highest larval index.

It has been shown that insecticide-treated bed nets or curtains may reduce morbidity and mortality from malaria in hyper-holoendemic areas of sub-Saharan Africa. This protection could partially depend on the transitory imbalance between the anti-malaria immunity acquired by the population before the intervention and the lowered sporozoite load resulting from the anti-vector measure. To verify if the efficacy of the intervention is influenced by the baseline immune status of the population, we compared the protective effect of permethrin-impregnated curtains (PIC) against malaria infection among groups with different baseline levels of anti-malaria immunity. We analyzed the impact of PIC on the Plasmodium falciparum infection rate in two rural villages of Burkina Faso inhabited by three ethnic groups: the Fulani, Mossi, and Rimaibé. These have been previously shown to differ for several malariologic indices, with the Fulani being characterized by lower infection and disease rates and by higher immune response to P. falciparum with respect to the other ethnic groups. The PIC were distributed in June 1996 and their impact on malaria infection was evaluated in groups whose baseline levels of immunity to malaria differed because of their age and ethnic group. Age- and ethnic-dependent efficacy of the PIC was observed. Among the Mossi and Rimaibé, the impact (parasite rate reduction after PIC installation with respect to the pre-intervention surveys) was 18.8% and 18.5%, respectively. A more than two-fold general impact (42.8%) was recorded in the Fulani. The impact of the intervention on infection rates appears positively correlated with the levels of anti-malaria immunity. Since decreased transmission entails a reduction of immunity, the efficacy of the intervention in the long term cannot be taken for granted. The expected complementary role of a hypothetical vaccine is stressed by these results, which also emphasize the importance of the genetic background of the population in the evaluation and application of malaria control strategies.

The traditional view of interactions between arboviruses and their arthropod vectors is that vector hosts become increasingly resistant to parasites; parasite attenuation occurs; or through the process of coevolution, resistance and attenuation occur in concert. Detrimental effects from arboviruses are only seen when vector and virus are not yet well adapted. Results from this study indicate that eastern equine encephalomyelitis (EEE) virus reduces survival and reproduction (fitness) of the mosquito Culiseta melanura, which is required for transmission of EEE virus in North America. Mosquito virulence was not measurably attenuated in virus isolates recovered 55 year apart. This virus did not affect the ability of mosquitoes to obtain a blood meal or the rate of mosquito oocyte development. Results from this study support those from earlier investigations with other mosquito-virus interactions and suggest that reproductively successful arboviruses can have detrimental effects on their mosquito vectors.