Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Division of Microbiology and Infectious Diseases, Southwest Foundation for Research and Education, Bethesda, Maryland 20014
African, gelada and hamadryas baboons were exposed to between 500 and 4,000 Schistosoma haematobium cercariae each and followed for up to 2 years before post mortem study. The schistosomes developed well in all species of baboon, but many worms died after the first year of infection. Most worms and eggs were found in the mesenteric circulation, but marked involvement of the bladder and ureters with hydroureter and hydronephrosis were frequently seen. Egg concentration in the ureters was similar to that in the bladder. Ureteral stricture was uncommon, and the pathogenesis of most hydroureter and hydronephrosis appeared to be functional. Massive involvement of male and female internal genitalia was frequent. Active lesions with marked acute inflammation appeared to continue for prolonged periods without marked residual in some animals infected for 2 years, while marked fibrosis was seen less than a year after infection in other animals. Also, calcification of eggs in the tissues was not a function of duration of infection. The duration of infection thus appeared not to be of fundamental pathogenetic importance, but the relevance of this conclusion to infections in man is questionable. Massive accumulation of calcified eggs in tissues, as noted in man, did not occur in the baboons, apparently because of differing host-parasite relations rather than because of the relatively short duration of infection in baboons. Baboons exposed repeatedly to small numbers of cercariae were partially resistant to new infections and showed a lower proportion of eggs in the urogenital system than did animals exposed only once.