Study of a population of Biomphalaria tenagophila (Orbigny, 1835) and of schistosomiasis transmission in "Alto da Boa Vista", Rio de Janeiro

Abstract

The present study was performed using data from a Biomphalaria tenagophila population located in a watercress garden in the Alto da Boa Vista region representing an isolated focal point of schistosomiasis in the city of Rio de Janeiro. The density and age structure of this B. tenagophila population and its rate of infection by Schistosoma mansoni were studied for a period of 15 months. The snail population showed seasonal variation in density, with a decrease in number of individuals at the beginning of the rainy season. At the end of this season, the population consisted mainly of adults (92.8% in May 1985 and 82.8% in April 1986). The population growth curve was logistic and of sigmoidal configuration. Schistosoma mansoni cercariae were eliminated over a short period of time (March, April and May 1986). The release of cercariae of S. mansoni and of birds seems to depend on environmental temperature, which during certain months would show a daily variation of up to 13 degrees C, with the lower thermal limit approaching the limit value for sporocyte development.

Schistosomiasis mansoni in Bananal (State of São Paulo, Brazil): II. Intermediate hosts

“…Concerning the shedding of cercariae, it was predominant in Pernambuco (Northeastern Brazil) during the dry season, as observed in Bananal, while the same occurred in Rio de Janeiro dur-L a ra n je ir a s R io B a n a n a l C e n tr o ing the rainy season. The slight variations in pH and temperature, observed during this study produced changes in snail population densities and the transmission of the infection, in agreement with the conclusions of Camargo (1977), Baptista et al (1989) and Baptista and Jurberg (1993). As regards water temperature, Ramos et al (1961) captured infected B. tenagophila specimens in the Valley of River Ribeira de Iguape during the winter, the water temperature being less than 19°C as a consequence of which the snail population density is lowest.…”

“…In recent years, Dias et al (1989) andMarçal Jr. et al (1991), when examining snails from the municipality of Pedro de Toledo, in the valley of River Ribeira de Iguape, obtained similar results. The percentages of shedding snails were comparable to those recorded by Barbosa and Costa (1961), Baptista et al (1989), Cutrim and Coura (1992) and Coura Filho et al (1996) Brazil (1998Brazil ( -2001.…”

“…Pinotti et al (1960) in the State of Pernambuco (Brazil), Baptista et al (1989) and Baptista and Jurberg (1993) in the State of Rio de Janeiro, observed similar effects of the amount of rainfall. Concerning the shedding of cercariae, it was predominant in Pernambuco (Northeastern Brazil) during the dry season, as observed in Bananal, while the same occurred in Rio de Janeiro dur-L a ra n je ir a s R io B a n a n a l C e n tr o ing the rainy season.…”