Influence of temperature on development of Schistosoma mansoni female cercariae in Biomphalaria glabrata.

In these experiments the ratio of male to female S. mansoni larvae in B. glabrata from Belo Horizonte and Ribeirão das Neves Minas Gerais, Brazil, either reared in laboratory or collected in the field, varied from 1:1 to 1:1.3 or 1.4:1. Cercariae of LE strain of Schistosoma mansoni, shed by 39 snails maintained at 25 +/- 0.5 degrees C were used to infect mice on a weekly basis. Subsequent perfusion resulted in 76.6% male and 23.4% female worms. The cercariae produced by 32 infected snails maintained at 27 +/- 0.5 degrees C were inoculated into mice and produced 43.4% male and 56.6% female worms (p < 0.05). Cercariae eliminated by snails collected in Barreiro and Ressaca, Belo Horizonte, during hot months, produced 45.7 to 47.7% male and 52.3 to 54.3% female worms. A lower number of cercariae shed by snails collected in Gorduras, Belo Horizonte, at 20 +/- 3.0 degrees C, produced 51.6% male and 48.4% female worms. Thus, in this region the infection of vertebrate hosts with S. mansoni cercariae would be more severe in the summer due to the higher level of parasites and the number of eggs.