Schistosomiasis mansoni in an area of low transmission. II. Risk factors for infection.

Risk factors for Schistosoma mansoni infection were identified using a 1:1 matched case-control design. The work was conducted in the municipality of Pedro de Toledo, São Paulo State, Brazil, an area where the snail host is Biomphalaria tenagophila. Information on water contact patterns, knowledge, attitudes and practices (kap), socioeconomic and sanitary conditions were obtained by mean of questionnaires. The crude odds ratio estimates and the adjusted odds ratio estimates using the logistic regression model are presented. Most of the examined individuals admitted recent water contacts (90.6% of the cases). The most frequent reason for contact was swimming, playing and fishing and the preferential site of contact was the river. According to the logistic regression technique, the main risk factors for infection were: a) water contact through swimming, playing and fishing; b) fording; c) bad hygiene. We concluded that recreational activities are the main reasons for schistosomiasis transmission in Pedro de Toledo and leisure alternatives should be offered to the local population.

[Control of schistosomiasis mansoni in an area of low transmission]. / Controle da esquistossomose mansônica em área de baixa transmissão.

The schistosomiasis is transmitted by Biomphalaria tenagophila in our study area (Pedro de Toledo, São Paulo, Brazil). From 1980 to 1990 epidemiological surveys in a population of 4,000 inhabitants, has shown that: prevalences by Kato-Katz (KKT), immunofluorescence (FT) and intradermal (IDT) techniques were 22.8%, 55.5% and 51.8%, respectively; intensity of infection was low, 58.5 eggs per gram of faeces (epg); there were no symptomatic cases; prevalences were higher in mates, children and rural zone; index of potential contamination was 57.5% in the age group 5 to 20 years; 2/3 of patients were autochthonous; cases were no-randomly aggregated; transmission was focal and only 0.4% of snails were infected; water contacts through recreation showed the most important odds ratio; knowledge, attitudes and practices were satisfactory. From the epidemiological findings a control programme was carried out: yearly faeces exams, chemotherapy, molluscocide, health education and sanitation. Thus, the prevalence decreased sharply to 3.3% and intensity of infection to 30.3 epg; the incidence rates ranged between 0.4% and 2.5% annually; the sanitation became better and the youngsters were the main target in prophylaxis. To improve control, immunodiagnosis has to be conducted and the involvement of the population should be increase. However, we cannot forget that re-infection, therapeutic failure, etc, could play a major role in the maintenance this residual prevalence.

Schistosomiasis mansoni in an area of low transmission: I. Impact of control measures

Este trabalho foi realizado no municipio de Pedro de Toledo, no Estado de Sao Paulo, Brasil, em 1987 para esclarecer aspectos sobre niveis de transmissao ao homen de Schistosoma mansoni, quando o hospedeiro intermediario e Biomphalaria tenagophila. Desde 1980 vem sendo desenvolvido um programa de controle neste municipio. Foram submetidos a exames de fezes (metodo de Kato-Katz) 4719 individuos das zonas rural e urbana. A taxa de prevalencia foi de 4,8 por cento, sendo maior nos homens (6,2 por cento) e tambem na zona rural (5,8 por cento). Foi de 35,1 por cento a media de ovos de S. mansoni por grama de fezes (epg). Cerca de 80,0 por cento dos portadores apresentavam menos de 100 epg e somente 20 individuos (9,0 por cento) eliminavam mais do que metade do total de ovos. Os mais altos indices de potencial de contaminacao (IPC) ocorreram nos grupos etarios de 5 a 20 anos (57,6 por cento). Dois tercos dos pacientes investigados (207) eram autoctones de Pedro de Toledo. A distribuicao geografica dos portadores demonstrou evidente agregacao dos casos autoctones, assim como uma intima associacao entre locais de contato da populacao com os criadouros de B. tenagophila. Este estudo demonstra que os portadores de S. mansoni nao estao agregados ao acaso, que os jovens devem ser o principal objetivo na profilaxia e que o programa de controle foi eficaz.

Schistosomiasis mansoni in an area of low transmission. I. Impact of control measures.

This work was undertaken in the municipality of Pedro de Toledo (São Paulo State, Brazil) in 1987, to clarify aspects related to the transmission levels of Schistosoma mansoni in a human population where the snail host is Biomphalaria tenagophila. Since 1980 a control programme has been undertaken in this municipality. Urban and rural populations (4,719 subjects) were submitted to faecal examinations (Kato-Katz method). The overall prevalence rate was 4.8% being higher in males (6.2%) and also in the rural zone (5.8%). The geometric mean of S. mansoni eggs was 35.1 eggs per gramme of faeces (epg). Approximately 80.0% of the carriers presented less than 100 epg and only 20 individuals (9.0%) eliminated more than half of total eggs. The highest index of potential contamination (IPC) was in the age group of 5 to 20 years (57.6%). Two thirds of the investigated patients (207) were autochthonous of Pedro de Toledo. The geographical distribution of the carriers showed a clear aggregation of the autochthonous cases and a close association between human contact sites and breeding places of B. tenagophila. This study shows that schistosomiasis subjects were not randomly aggregated, the youngsters should be the main target in the prophylaxis, and the efficacy of the control programme.