Pathogenesis of Venezuelan Equine Encephalomyelitis Virus Infections in the Developing Chick Embryo

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Abstract
The pathogenesis of the infection produced by the Venezuelan equine encephalo-myelitis virus in chick embryos was investigated in an attempt to discover biol. differences between this virus and the Eastern and Western equine encephalomyelitis viruses. The virus was cultivated through 20 generations in the developing chick embryo by yolk-sac passage and through 58 generations by membrane passage. It resembled the Eastern and Western viruses in rate of multiplication. It reached its maximum titer at about the time gross evidence of infection of the embryo was first manifest, i.e., several hrs. before death. The virus was found to be disseminated throughout the egg, but the highest cone, was always in the embryo. No change in the virulence of the virus for mice was encountered as a result of the membrane passages. The pathologic changes produced by the virus are not specific for the infection, which in its final stages results in a generalized destruction of tissues. Chick embryos are as susceptible to the virus as are mice. The behavior of the Venezuelan virus in the chick embryo resembles that described for the Eastern and Western viruses.