Parasitological, clinical, and histopathological observations on 54 baboons infected with Schistosoma mansoni are presented. The baboon and S. mansoni constitute a compatible host-parasite system, evidenced by the infectivity of cercariae (98% penetration, 42% adult worm recovery), and the long, fertile life of the worms. Baboons tolerated the infection well, with clinical illness a rarity in moderately infected baboons. Pathological findings were generally unremarkable. An acute “toxemic” phase occurred 66 days or less following a large cercarial exposure in three baboons. Worm burdens were not significantly reduced during the course of prolonged infection, but prolonged infections resulted in decreased oviposition by the worms and in an anterior shift in egg deposition from the colon to the small intestine. Concomitant immunity was also a feature of baboon infections. Decreased oviposition and the anterior shift are probably manifestations of a second phase of immunity, distinct from concomitant immunity. The baboon is similar to man and the grivet monkey in that in all three species immunity is slow to develop.
Southwest Foundation for Research and Education, San Antonio, Texas 78228.
Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20014.
College of Veterinary Medicine, University of Georgia, Athens, Georgia 30602.