Volume 31, Issue 4
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



Stool surveys were conducted on children 2–10 years of age in 27 villages within Dacca District and around this index area (1,668 children were sampled), revealing an endemic focus of infection to the south and the east of Dacca District. In order to determine the seasonal variation in the total snail populations and the natural rate of infection in the snails, two species of planorbid snails, and , were periodically sampled for 12 months from a village endemic for infection. Gymnocephalous cercariae were found in snails during August, September and October. The size of the snail population (n = 1,275) was significantly correlated with inches of rainfall ( = +0.62; < 0.05) and water temperature ( = +0.59; < 0.05). The natural infection rate of in the snails ranged from 0.5–2%. Snails from non-endemic areas were exposed to 3–10 miracidia. A total of 13 of 49 (27%) of and 6 of 14 (43%) of had gymnocephalous cercariae present 4 to 6 weeks after exposure to miracidia. Thus, snail strain variation is unlikely to be a barrier to transmission.


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