Infection of Mice by Feeding of Tissues Containing the Virus of St. Louis Encephalitis. ∗

Abstract

In attempts to determine whether the injection of young mice would serve as a method for the detection of smaller amounts of virus, newly born, unweaned Swiss mice have been inoculated intracerebrally or intranasally with tenfold dilutions of suspensions of infected adult mouse brains. These mice have been found susceptible and preliminary experiments suggest the possibility that newly born mice will succumb to one-tenth the dose necessary to kill grown mice by the respective routes.

In the course of these experiments it has been noted frequently that the mothers had devoured their dead or moribund offspring. In 3 of such cases the mothers were found dead after intervals of 5 to 7 days. This suggested the possibility of the mothers having contracted the infection by feeding and accordingly the brain of the last one was tested by passage to other mice and found to contain virus. In addition, grown mice of both sexes were allowed to feed on moribund or dead, newly born mice previously infected with virus by the intracerebral route and in 2 of 7 instances the mice died or were sick 7 days after feeding. From these, virus was obtained from the brain by passage to grown mice. A few experiments performed so far, in which mice have been allowed to eat infected adult mouse brains, have all failed to result in clinical infection. This is in agreement with the findings of Brodie. 1

The importance of the observation that adult mice can be infected by eating the bodies of infected, newly born mice, is that this mode of entry may have epidemiological significance. It is the only mode of entry so far described in which this infection has been transmitted from mouse to mouse by some natural means and not by inoculation.