Abstract
Mice given an intranasal instillation of louping-ill virus, following an incubation period of 6–7 days, regularly develop signs of encephalitis and die 8–10 days after inoculation with characteristic lesions in the central nervous system. 1 , 2 Studies on the presence of the virus in blood and brain of intranasally inoculated mice will now be reported.∗
White-face and Swiss mice have been inoculated by dropping into the nose 0.03 cc. of a 1 to 10 suspension in physiological salt solution of the brains of mice dying of louping-ill. The virus content of the blood has been studied in 2 ways. In one experiment mice were inoculated and bled twice daily from the tail for 8 to 9 days—that is, until dead. One or 2 drops of blood were collected in 0.25 cc. of a solution of heparin, 1–1,000 in salt solution, and 0.03 cc. of this was inoculated into each of 2 other mice. In the second case, 36 mice were inoculated and 4 were killed daily, the whole blood being withdrawn directly from the heart and inoculated immediately into 2 mice. The mice were then killed, the brains removed and emulsified, and this suspension was also inoculated into other mice.
The results of these experiments showed that virus did not appear in the blood stream of nasally infected mice in quantity until the 2nd day after inoculation. From then on to the 6th day, when the mice became sick, the virus was usually demonstrable in the blood. After the 6th day, until the animals were moribund, the virus tended to disappear. The brains of these mice occasionally contained demonstrable virus as early as the first day but in 50% of cases not until the 3rd day. After the 3rd day the virus was invariably present in large amounts.
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