Adaptation of Leon Strain of Poliomyelitis to Mice

Abstract

Monkey passage Leon strain of poliomyelitis was inoculated intra-spinally into C3H mice After 15 days incubation paralysis and death occurred. Spinal cords yielded a virus which on passage produced flaccid paralysis, more frequently of the front legs, after 4 to 6 days'' incubation. This virus has been maintained for 35 intraspinal passages. It fails to infect mice by intracerebral inoculation and has low virulence by intraspinal route (10-1.5 50% end point). After 8, 20 and 27 mouse passages this virus,when given intracerebrally to monkeys, produced typical clinical and histopathological poliomyelitis. Neutralization tests in mice using immune serum to monkey Leon virus against mouse passage virus showed specific neutralization,whereas results with anti-Brunhilde and anti-Lansing sera were essentially negative. No neutralization could be demonstrated with anti-Theiler''s and anti-encephalo-myelocarditis virus sera. Low neutralization indices were obtained with human gamma globulin. A neutralization test in monkeys was also positive. Cross immunity tests in monkeys between mouse and monkey Leon viruses were positive. The mouse virus failed to propagate in the chick embryo.