Schistosoma mansoni Infections in Cercopithecus sabaeus Monkeys

Abstract

Cercopithecus iabius (green) monkeys discharged eggs up to 3.5 years after initial exposure and for a comparable period after reexposure. The number and development of worms from challenge infections were similar to initial infections, but excretion of eggs was delayed after challenge. Monkeys exposed repeatedly to moderate or small numbers of cercariae tolerated a burden of worms that would have been lethal as a single initial infection. There was evidence that worms lived for 5 years, and without regression in size. Large accumulations of eggs still occurred in the liver and intestine after 5 years, and the relative numbers of immature, mature, and degenerate eggs were similar to early stages of first infections. The response of the green monkey to S. mansoni is in marked contrast to that of Macaca mulatta, which suppresses excretion of eggs after 6 to 9 mo. and quickly acquires strong resistance to challenge infections. The longer output of eggs by the green monkey is more like what occurs in man. A corresponding comparison of acquired resistance is not possible because too little is known about resistance imposed against schistosomes in the human host. The rhesus and the green monkeys may provide a valuable experimental model for investigating the immune mechanism against schistosomes. The green monkey may be useful in the evaluation of schistosomicidal drugs.