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Studies on Chick Embryo Adapted Rabies Virus

I. Culture Characteristics and Pathogenicity

From the Section of Viral and Rickettsial Research, Lederle Laboratories Division, American Cyanamid Company, Pearl River, New York

Abstract

Four strains of rabies virus, one chick-brain fixed (Flury) and three street strains were adapted to the developing chick embryo. The Flury strain was passaged through 80 chick embryo generations by yolk-sac inoculation of infected chick embryo tissue.

The virus multiplied slowly in the fertile hens' eggs and reached its maximal titer on the ninth to tenth day after inoculation. The virus was distributed throughout the egg, with possible exception of the allantoic fluid, the highest concentration being present in the embryo. Death of the infected embryos, inoculated at 7, 9 and 11 days of age, occurred as a rule immediately before or at the time of hatching. When 15-day or older fertile eggs were inoculated most of the embryos hatched but the virus was "carried over" to the newly hatched chicks causing either death or development of homologous antibodies in the survivors.

The LD₅₀ titer of infected embryo suspensions remained within the range of 10^–4.50 to 10^–5.50 for mice, guinea pigs, cotton rats and chicks throughout the cultivation period. The intracerebral titration of the Flury strain in rabbits yielded highly irregular results which were discussed in relation to the "self-sterilizing neuro-infection" phenomenon.

The invasive power of the Flury strain for parenterally inoculated rabbits seemed to be entirely lost, and the virulence of the strain for hamsters and guinea pigs seemed to undergo some attenuation during the series of passages in the developing chick embryo.