EFFECT OF SOME ENVIRONMENTAL-CONDITIONS AND FINAL-HOST-RELATED AND PARASITE-RELATED FACTORS ON THE PENETRATION OF SCHISTOSOMA-MANSONI CERCARIAE INTO MICE

The capacity of Schistosoma mansoni cercariae to penetrate mouse tail skin was studied under selected environmental exposure conditions and in relation to some parasite-and final-host-related factors. Mice were exposed to non-labelled or75Se-methionine labelled cercariae using the tail immersion technique. The number of cercariae which penetrated of the amount of tail-bound radioactivity was used to express the host-penetrative capacity of the larvae under various experimental conditions. The minimum temperature for host-penetration was 7° C. The ability to penetrate increased significantly at 10° C and 12° C and the optimum number of cercariae which penetrated was in the range between 14° C and 36° C. At temperatures above 36° C the number of cercariae which penetrated was reduced dramatically. The skin-penetration capacity was unaltered up to a salinity level of 2.4‰ while at salinity levels above 2.4‰ the ability to penetrate gradually decreased. The host-finding capacity was reduced in distilled water and in water with high levels of turbidity. A comparison of cercarial exposure in six types of water revealed comparable skin-penetration capacity. Final-host-related factors such as strain of mice, weight, sex, exposure under anaesthesia, and fixation of the tail, in general did not influence cercarial penetration. Previous heterologous infections with the nematode Syphacia sp. or the trematode Echinostoma revolutum had no influence on penetration. The penetration capacity of cercariae into tails of dead mice was reduced. © 1979 Springer-Verlag.