Studies on the Growth of Murine Encephalomyelitis Viruses in Fertile Eggs

Abstract

Theiler's virus of mouse encephalomyelitis, FA strain, was cultivated through ten generations in the developing chick embryo by the chorio-allantoic route of inoculation. Successful propagation was also obtained by inoculation into the yolk-sac and into the allantoic cavity. The virus was present throughout the egg with the highest concentration being found in the embryo, after twelve to fourteen days incubation at 35 C., following inoculation of 6–7 day old eggs. The ID₅₀ titers of embryo suspensions ranged between 10^−5.0 and 10^−5.4 and no changes in the symptomatology of infection by this virus in mice were observed following these egg passages. Theiler's TO strain of mouse encephalomyelitis was also passed through four generations in the developing chick embryo following inoculation by the chorio-allantoic route. Virus was found to be present in the chorio-allantoic membrane and embryo and the maximal titer appeared to be found after twelve days incubation at 35 C. The ID₅₀ titer of the embryo suspension after four egg passages was found to be 10^−3.0. Successive passages in the chick embryo did not cause any apparent alteration in the symptomatology produced by this virus in mice. Efforts to cultivate in fertile eggs the Lansing, Y-SK and Ph strains of mouse-adapted poliomyelitis virus, two strains of poliomyelitis virus derived from monkey spinal cord and one strain of poliomyelitis virus derived from human spinal cord, were unsuccessful.