The efficacy as an immunizing agent of the Kenyan strain of Schistosoma mansoni against challenge infection in rhesus monkeys was demonstrated. An initial exposure of 200 cercariae immunized monkeys against a challenge dose of 2,000 cercariae administered 16 weeks later. The penetration rate in rhesus monkeys was 99%, the same as in baboons. The prolongation of the time for immunity to develop in baboons, compared to rhesus monkeys, shown with this strain of S. mansoni is therefore not due to a reduced potential for immunization by this strain in the rhesus monkey.
Southwest Foundation for Research and Education, San Antonio, Texas 78228.