An attempt was made to demonstrate acquired resistance to Schistosoma mansoni infection in mice and hamsters. In one series of experiments, mice with light bisexual S. mansoni infections were challenged with an exposure great enough to kill uninfected mice. The survival pattern of the superinfected mice was significantly different from that of the controls in that the deaths were spread out over a much longer period. Apparently some of the mice were sufficiently immunized so that they were able to survive longer than the controls. In another set of experiments infected mice and hamsters were similarly challenged. Later, total worm counts were made and it was found that significantly fewer new worms developed in the superinfected animals than in the controls. These findings demonstrate that mice and hamsters develop resistance to reinfection with S. mansoni.
Laboratory of Tropical Diseases, National Microbiological Institute.
Biometrics Section, National Cancer Institute.
The writers wish to express their appreciation to Mr. Ned M. Etherington for his technical assistance in the study.