Abstract
Workers have reported the successful transmission of a virus isolated from cases of the St. Louis epidemic of encephalitis to monkeys 1 and to monkeys and mice. 2 ,3 Through Dr. Holden of the College of Physicians and Surgeons was obtained some of the virus used by Dr. Armstrong which had undergone 13 serial passages in white mice. The intracerebral infective dose of the virus varied between 0.03 cc. × 10-3 to 0.03 cc. × 10-6 during the course of this work.
The present work deals with experimental passage of the virus, its preservation, and its resistance to germicides. White mice showed a fairly uniform susceptibility to the virus. After 3 to 5 days'incubation, the animals developed a hyperirritability, ataxia, convulsions and paralysis. Mice receiving attenuated virus or borderline infective doses developed very mild attacks, with tremors lasting only a day or two. Of 4 such animals tested, one showed immunity against subsequent infection.
Attempts to pass the virus to guinea pigs, rabbits, rats, kittens and ferrets were negative. Intracerebral and intraperitoneal inoculations in 5- to 6-weeks-old rats and 24-hour to 6-months-old guinea pigs were done and in many instances were redone at intervals.
One monkey, given 1 cc. intracerebrally (motor cortex) and 2 cc. intraperitoneally of a 10% suspension of the 26th passage in mice, developed a rise in temperature after 4 days, followed by a general slowness and awkwardness, tremors and ataxia. When sacrificed 3 days later, these symptoms were still manifest. Since others had found the maintenance of the virus strain through monkeys difficult, it was decided to use for serial passage those parts of the monkey's central nervous system that contained the most virus.
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