Susceptibility of Wild Mice to the Virus of St. Louis Encephalitis. ∗

Abstract

For the last 2 years we have been concerned with the question of possibility of a reservoir in animals of the virus of St. Louis encephalitis. Since this has been an interepidemic period, our method of study has been to determine experimentally the susceptibility of various species. Among others, wild gray house-mice (Mus musculus) have been tried and found susceptible.

Up to the present, virus has been carried (by intracerebral inoculation) through 10 passages in wild mice and has retained its infective titer as tested on Swiss mice. Furthermore, a test with rabbit antiserum showed specific protection against passage virus. In addition to the intracerebral route we have also succeeded in transmitting the infection to wild mice by the intranasal route.

In another series of experiments we have found it possible to transmit infection to Swiss mice by feeding infected material but in a single experiment so far performed have failed to infect a wild mouse by this route. The investigation is still in progress and this fragmentary report is made at this time because of the possibility of human cases occurring again this summer, at which time it would be desirable to look for virus in wild mice trapped in the households where cases have occurred.