Although vaccination of guinea pigs with formalin-inactivated Western equine encephalomyelitis virus rendered them specifically immune to an intracerebral challenge dose of 1,000 M.L.D. of Western virus, it failed to protect their central nervous system against the initial effects of the virus: the intracerebral challenge dose was followed by an abortive infection of 20 to 30 hours' duration characterized by fever and histopathological changes which simulated the response at that early stage of non-vaccinated control animals.

During the abortive infection of immune animals, virus could occasionally be demonstrated in their brains; indeed, it was detected with about the same frequency it was isolated from brains of similarly inoculated, non-immune guinea pigs during corresponding early phases of the infection. About one week after the abortive infection there was found a marked transitory accumulation of specific neutralizing antibody in the brain tissue.

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equalled at this time 1:1 to 1:10 instead of the value of about 1:300 found under physiological conditions.

Guinea pigs which had recovered from an abortive infection with Western virus were resistant for a limited period of time to the effects of intracerebral inoculations of the immunologically distinct viruses of Eastern equine encephalomyelitis or vesicular stomatitis.

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