The Biology of Schistosoma mansoni in Laboratory Rats

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Abstract
The course of infection with Schistosoma mansoni was studied in two strains of rats over a period of 40 weeks. An improved procedure was used for exposure of the animals to cercariae. Worm recovery rates in Sprague-Dawley rats each exposed to 1,000 cercariae were as follows: 4 weeks, 20 to 37%; 8 weeks, 4 to 7%; 16 weeks, 2 to 5%; 21 to 32 weeks, 2%; 40 weeks, 2%. Canadian Hooded rats gave similar yields. Exposures to reduced numbers of cercariae did not alter the 4-week recovery rate. However, an increased recovery (16%) resulted at 8 weeks in rats exposed to 250 cercariae. On the basis of worm recovery rates, Sprague-Dawley rats ranging in age from a few days to 24 months were equally susceptible to infection. Observations on the growth and survival of male and female worms showed that the natural defenses of the rat were more effective against female worms. But neither sex attained the sizes characteristic of worms from mice. There was a marked tendency for worms to inhabit the liver rather than the mesenteries of the rat Eggs were not found in the feces or intestines, and those in the liver were mostly immature, degenerate, or mere shells. A few miracidia were recovered, but these failed to produce infection in snails. The biology of S. mansoni was similar to Sprague-Dawley and Canadian Hooded rats. The use of the rat is discussed in relation to studies on the mechanisms of host resistance to S. mansoni.