The burden of Leishmania chagasi infection during an urban outbreak of visceral leishmaniasis in Brazil.

First noted in the city of Teresina in 1981, the last decades have witnessed a remarkable increase in urban transmission of American visceral leishmaniasis (VL) in many Brazilian cities. Teresina, the site of this study, has faced two large outbreaks of VL. The first occurred from 1981-1985 when almost 1000 new cases were reported. The second started in the 1990s, and between 1993 and 1996 more than 1200 new cases were detected. This report describes the prevalence of infection with Leishmania chagasi in Teresina at the end of the second outbreak and gives estimates of the number of people who became infected during the epidemic. Between June 1995 and May 1996, 200 households were chosen at random from a list of addresses covering about 93% of Teresina's urban households. In each household, one person over the age of 1 year was screened for Leishmania antibodies and skin-tested. Nearly 50% of persons had a positive leishmanin reaction, but only 13.9% had detectable antibodies to L. chagasi. While prevalence estimates based on the leishmanin skin-test increased with age (P<0.001), those based on serological tests showed a lesser, and non significant, variation with age (P=0.31). Using a geometric growth equation, and assuming that the annual distribution of clinical cases may serve as an approximation to what would have been the distribution of infections by year, we estimated that over 320000 persons were infected during the epidemic. Little is known about the epidemiology of VL in urban areas, where social networks, population density, and relationships of housing with the natural environment are more varied and complex than in the rural scene. In those areas, control interventions have failed to eliminate transmission of the parasite and prevent new epidemics. Further epidemiological studies of VL in urban areas might be needed to inform control actions.

Household structure and urban services: neglected targets in the control of visceral leishmaniasis.

Visceral leishmaniasis (VL) caused by Leishmania chagasi is a growing public-health problem in many parts of the New World. Although several studies have focused on the consequences of environmental damage, human migration and land occupation on the incidence of VL, the effects on the disease of the substandard living conditions that often result from the process of urbanization have not been investigated in detail. The present study was based in the Brazilian city of Teresina, where, since 1980, there have been two large outbreaks of VL (one in 1981-1985 and the other in 1993-1996), each involving at least 1000 newly reported cases. The role of household structure and the provision of urban services in the city, as predictors of the occurrence of VL, was studied in a case-control investigation. After controlling for age, crowding, and the background incidence of VL in the area where the subjects lived, the risk of acquiring the disease was found to be significantly higher for those who lived in houses with an inadequate sewage system and those who had no regular rubbish collection. Improving household structure and providing basic urban services might be effective strategies for controlling the spread of VL in urban areas.

Competence of the human host as a reservoir for Leishmania chagasi.

The failure of control programs for visceral leishmaniasis (VL) that depend on elimination of infected dogs suggests that other reservoir hosts may participate in the transmission cycle. To determine whether persons infected with Leishmania chagasi can infect the vector sand fly, laboratory-reared Lutzomyia longipalpis were allowed to feed on Brazilian subjects with active, cured, and asymptomatic VL and on asymptomatic residents of houses of persons with active VL. Of 3747 insects that had fed, 26 acquired infection from 11 of the 44 persons with active VL, but none acquired infection from the 137 asymptomatic persons. Among persons <4 years old with active VL, a history of diarrhea and higher peripheral blood neutrophil counts were independent predictors of infectivity. Further experiments using larger numbers of insects are necessary to evaluate the reservoir competence of persons with asymptomatic infections, who represent a large segment of the population of several Brazilian cities.

Mannan-binding lectin enhances susceptibility to visceral leishmaniasis.

Levels of the serum opsonin mannan-binding lectin (MBL) were directly correlated with the probability of developing visceral leishmaniasis. Monocytes infected with MBL-opsonized Leishmania chagasi promastigotes secreted higher levels of tumor necrosis factor alpha and interleukin-6 than cells infected with nonopsonized parasites. Our findings indicate that MBL can modulate the clinical outcome of infection with L. chagasi and the function of infected macrophages.