Non-fatal Infection of Mice following Intracerebral Inoculation of Yellow Fever

Although the rhesus monkey (Macaca mulatta) was the first laboratory animal found to be suitable for experimental work with the virus of yellow fever (1, 2), the laboratory mouse has also played an important rble in yellow fever research. However, efforts to define more exactly the susceptibility of this animal have been few since the initial demonstration in 1930 that mice could be infected (3) and certain supplementary studies (4, 5) reported shortly thereafter. Basically, these early studies demonstrated the following: that adult mice are highly susceptible to virus inoculated by the intracerebral route (3, 5) but can be infected regularly by extraneural routes only after the brain has been traumatized (4); that baby mice, in contrast, are highly susceptible to virus inoculated extraneurally (3); and that mice of several different strains are not equally susceptible (4, 5). Recently reported studies of the susceptibility of mice to yellow fever virus have been chiefly concerned with the susceptibility of young mice to extraneurally inoculated virus with special reference to the practicability of their use in protection tests (6) and in testing for the presence of small amounts of virus (7). In studies now being terminated in this laboratory the exact relation of age to the susceptibility of mice to several strains of virus, inoculated by extraneural routes, has been worked out (8), and it has been shown in addition that significant differences related to age exist in the susceptibility of mice inoculated by the intracerebral route, the youngest mice being the most susceptible to infection (9). The present paper reports observations indicating the occurrence of specific but non-fatal infections among mice inoculated intracerebrally with yellow fever virus. A study has been made of the nature and course of such infections, and of the relation of their occurrence to the strain of virus employed and the dose inoculated. Materials and Methods