Poliomyelitis in chimpanzees; studies in homologous and heterologous immunity following inapparent infection.

The response of eighteen chimpanzees to poliomyelitis virus administered orally and cutaneously has been studied. There were no signs of weakness or paralysis in any of the animals. Sixteen of the eighteen (89 per cent) became infected as measured by intestinal carriage of virus. Only one of twelve was reinfected when challenged with an homologous (or homotypic) strain by the same routes, but seven of ten were reinfected on heterologous challenge. A correlation between the development of humoral antibodies and resistance to reinfection was demonstrated. During the course of these experiments, two chimpanzees acquired inapparent poliomyelitis by accidental contagion in the laboratory.