Rodney H. Duvall

Lack of resistance to Schistosoma japonicum in mice immunized with irradiated S. mansoni cercariae

Mice immunized with irradiated Schistosoma mansoni cercariae were resistant to challenge with S. mansoni cercariae (mean resistance 53%) but not to challenge with S. japonicum cercariae (mean resistance -5%). Furthermore, the antibodies induced by vaccination with irradiated S. mansoni cercariae were more reactive with S. mansoni than with S. japonicum schistosomula. These results support the concept that the resistance induced by vaccination with irradiated cercariae is immunologically specific.

Hepatic fibrosis in Schistosoma haematobium-infected mice

Swiss mice were exposed subcutaneously to 270 to 500 Schistosoma haematobium cercariae and killed 13 to 52 weeks later. Less than 10% of applied cercariae were recovered as worms, and the rate of oviposition by adult worm pairs was generally low. However, the adult worms survived well, the females contained an average of 56 eggs one year after infection, and numerous mature eggs were present in the tissues. All worms were located in the portal venous system. S. haematobium eggs in the liver elicited marked fibrosis, comparable to the fibrosis induced by S. mansoni infection. Only minimal fibrosis is seen around S. haematobium eggs in the liver of numerous other species, including man, the chimpanzee, other non-human primates and hamsters. Our findings illustrate the diverse relationships often seen between a single schistosome species and its mammalian hosts and emphasize the uncertainty in predicting the outcome of human schistosome infections from the study of experimental hosts.

Schistosoma japonicum: Migration of adult worm pairs within the mesenteric veins of mice

Mice infected with a single worm pair of a Japanese, a Philippine and a Formosan strain of Schistosoma japonicum were examined to determine the frequency of movement of worms within the mesenteric veins eight to 76 weeks after infection. By the 18th week after infection, one or more gross focal lesions developed in the gut, and 47 to 89% of eggs in the gut were concentrated in these lesions. In spite of this predominantly focal oviposition, oograms revealed first-stage eggs scattered throughout the gut, indicating frequent movement of the worms along the length of the intestine. Multiple gross lesions, often far from each other, were seen in half the mice. Our findings indicate that worms pairs move frequently, but that they are attracted to existing gross lesions, probably by substances released into the mesenteric blood from eggs or the surrounding inflammatory exudate.

Resistance of capuchin monkeys to reinfection with Schistosoma haematobium.

Capuchin monkeys were resistant to reinfection with Schistosoma haematobium one year after exposure to 500 cercariae, but worms in these monkeys continued to produce normal numbers of eggs. Monkeys were apparently completely refractory to reinfection when challenged 2-5 years after an initial exposure of 1000 to 2000 cercariae.