An ecological field study of the water-rat Nectomys squamipes as a wild reservoir indicator of Schistosoma mansoni transmission in an endemic area

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.

Abundância e infecçäo do molusco Biomphalaria glabrata pelo Schistosoma mansoni no Estado do Rio de Janeiro, Brasil / Abundance and Schistosoma mansoni infection of the snail Biomphalaria glabrata, Brazil

OBJETIVO:Investigar a distribuiçäo espacial, a abundância e os índices de infecçäo natural de Biomphalaria glabrata, hospedeiro intermediário do Schistosoma mansoni, em localidade do Estado do Rio de Janeiro, RJ, Brasil. MÉTODOS:Na localidade de Pamparräo, 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 Pamparräo e três de seus afluentes. Os moluscos capturados foram levados ao laboratório para diagnóstico da infecçäo. Para a análise dos dados, foram usados o coeficiente de Spearman (nível de 0,5 por cento 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 correlaçäo negativa com a pluviosidade. O afluente B destacou-se dos demais corpos d'água por apresentar taxas de infecçäo de B. glabrata elevadas (acima dos 25 por cento em alguns pontos de coleta) e persistentes. Foram encontrados mais moluscos infectados na estaçäo seca do que na chuvosa (?2=20,08; p=0,001). CONCLUSOES:A populaçäo de moluscos foi influenciada negativamente pelo regime de chuvas, principalmente no córrego Pamparräo. A época de estiagem também parece ter favorecido a ocorrência de infecçäo, provavelmente devido ao menor volume de água dos córregos, o que aumentaria as chances de encontro do parasita com seu hospedeiro intermediário

Schistosomiasis in a low prevalence area: incomplete urbanization increasing risk of infection in Paracambi, RJ, Brazil

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 por cento, mean intensity of 79 eggs per gram of stool and 47 por cento 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.