Small mammals are found naturally infected by Schistosoma mansoni, becoming a confounding factor for control programs of schistosomiasis in endemic areas. The aims of this study were: to investigate the infection rates by S. mansoni on the water-rat Nectomys squamipes during four years in endemic areas of Sumidouro, state of Rio de Janeiro, using mark-recapture technique; to compare two diagnostic methods for schistosomiasis; and to evaluate the effects of the chemotherapy in the human infected population on the rodent infection rates. The rodent infection rates of S. mansoni increased when rodent population sizes were lower. Coprology and serology results presented the same trends along time and were correlated. Serology could detect recent infection, including the false negatives in the coprology. The chemotherapy in the humans could not interrupt the rodent infection. Rodents can increase the schistosomiaisis transmission where it already exists, they probably maintain the transmission cycle in the nature and can be considered as biological indicators of the transmission sites of this parasite since they are highly susceptible to infection. The water-rats may present different levels of importance in the transmission dynamics of S. mansoni infection cycle for each area, and can be considered important wild-reservoirs of this human disease.

OBJETIVOS: Investigar a distribuição espacial, a abundância e os índices de infecção natural de Biomphalaria glabrata, hospedeiro intermediário do Schistosoma mansoni, em localidade do Estado do Rio de Janeiro, RJ, Brasil. MÉTODOS: Na localidade de Pamparrão, município de Sumidouro, RJ, as coletas de moluscos foram realizadas bimestralmente no período de junho de 1991 a novembro de 1995. Foram estabelecidos 23 pontos de coleta ao longo do córrego Pamparrão e três de seus afluentes. Os moluscos capturados foram levados ao laboratório para diagnóstico da infecção. Para a análise dos dados, foram usados o coeficiente de Spearman (nível de 0,5% de significância) e o teste de qui-quadrado. RESULTADOS: A abundância populacional de B. glabrata foi bastante variável ao longo do tempo e entre os ambientes amostrados. A maioria dos pontos de coleta apresentou correlação negativa com a pluviosidade. O afluente B destacou-se dos demais corpos d'água por apresentar taxas de infecção de B. glabrata elevadas (acima dos 25% em alguns pontos de coleta) e persistentes. Foram encontrados mais moluscos infectados na estação seca do que na chuvosa (chi²=20,08; p=0,001). CONCLUSÕES: A população de moluscos foi influenciada negativamente pelo regime de chuvas, principalmente no córrego Pamparrão. A época de estiagem também parece ter favorecido a ocorrência de infecção, provavelmente devido ao menor volume de água dos córregos, o que aumentaria as chances de encontro do parasita com seu hospedeiro intermediário.

OBJECTIVES: To investigate the spatial distribution, abundance and natural schistosomiasis infection levels in the snail Biomphalaria glabrata, the intermediate host of Schistosoma mansoni in an area of the State of Rio de Janeiro, Brazil. METHODS: In the Pamparrão area, Sumidouro county, RJ, Brazil, snail captures were carried out every other month from June 1991 to November 1995. There were 23 collecting sites along the Pamparrão stream and its three tributaries (A, B and C). Captured snails were examined in the laboratory for infection. Data analyses were performed using Spearman coefficient (0.5% significance level) and Qui-square test. RESULTS: The abundance of B. glabrata was variable in both time and space. Most of the collection sites showed a negative correlation with rainfall. The tributary B had the highest and most steady infection rates (more than 25% in some sites). There were found significantly more infected snail in the dry season (chi2 = 20.08; p=0.001). CONCLUSIONS: B. glabrata population in the Pamparrão valley was negatively influenced by rainfall, especially at the Pamparrão stream. The dry season seems to promote the infection probably due to the lower water volume, increasing the chance of interaction between the intermediate host and the parasite.

OBJETIVOS: Investigar a distribuição espacial, a abundância e os índices de infecção natural de Biomphalaria glabrata, hospedeiro intermediário do Schistosoma mansoni, em localidade do Estado do Rio de Janeiro, RJ, Brasil. MÉTODOS: Na localidade de Pamparrão, município de Sumidouro, RJ, as coletas de moluscos foram realizadas bimestralmente no período de junho de 1991 a novembro de 1995. Foram estabelecidos 23 pontos de coleta ao longo do córrego Pamparrão e três de seus afluentes. Os moluscos capturados foram levados ao laboratório para diagnóstico da infecção. Para a análise dos dados, foram usados o coeficiente de Spearman (nível de 0,5% de significância) e o teste de qui-quadrado. RESULTADOS: A abundância populacional de B. glabrata foi bastante variável ao longo do tempo e entre os ambientes amostrados. A maioria dos pontos de coleta apresentou correlação negativa com a pluviosidade. O afluente B destacou-se dos demais corpos d'água por apresentar taxas de infecção de B. glabrata elevadas (acima dos 25% em alguns pontos de coleta) e persistentes. Foram encontrados mais moluscos infectados na estação seca do que na chuvosa (chi²=20,08; p=0,001). CONCLUSÕES: A população de moluscos foi influenciada negativamente pelo regime de chuvas, principalmente no córrego Pamparrão. A época de estiagem também parece ter favorecido a ocorrência de infecção, provavelmente devido ao menor volume de água dos córregos, o que aumentaria as chances de encontro do parasita com seu hospedeiro intermediário.

OBJECTIVES: To investigate the spatial distribution, abundance and natural schistosomiasis infection levels in the snail Biomphalaria glabrata, the intermediate host of Schistosoma mansoni in an area of the State of Rio de Janeiro, Brazil. METHODS: In the Pamparrão area, Sumidouro county, RJ, Brazil, snail captures were carried out every other month from June 1991 to November 1995. There were 23 collecting sites along the Pamparrão stream and its three tributaries (A, B and C). Captured snails were examined in the laboratory for infection. Data analyses were performed using Spearman coefficient (0.5% significance level) and Qui-square test. RESULTS: The abundance of B. glabrata was variable in both time and space. Most of the collection sites showed a negative correlation with rainfall. The tributary B had the highest and most steady infection rates (more than 25% in some sites). There were found significantly more infected snail in the dry season (chi2 = 20.08; p=0.001). CONCLUSIONS: B. glabrata population in the Pamparrão valley was negatively influenced by rainfall, especially at the Pamparrão stream. The dry season seems to promote the infection probably due to the lower water volume, increasing the chance of interaction between the intermediate host and the parasite.

The risk of schistosomiais infection and heavy infection in the locality of Sabugo was evaluated in relation to housing in areas with different urbanization development and to residential supply with snail-infested water. Critical sanitary conditions were found in areas of incomplete urbanization, where healthy water supply sources were scarce, and draining of sewage, without previous treatment, was made directly to the water-bodies used for domestic and leisure activities, despite being Biomphalaria tenagophila snail breeding-places. Stool examinations (Kato-Katz and Lutz methods) showed prevalence of 2.9%, mean intensity of 79 eggs per gram of stool and 47% of positive cases presenting intense infection. The use of snail-contaminated water for domestic purposes was considered a risk factor for infection. It is concluded that incomplete urbanization would facilitate transmission, probably enhancing the intensity of infection and that a low prevalence could hide a highly focal transmission. The relevance of these facts upon the efficiency of epidemiologic study methods and disease control planning are then discussed.