Experimental infection of North American mammals with epidemic Venezuelan encephalitis virus

Eighty-three wild mammals of ten species were inoculated with a first mouse passage level Venezuelan encephalitis (VE) virus isolated from south Texas in 1971 during the VE outbreak. Rodents were highly susceptible to VE infection and circulated VE virus at levels ranging from 10(7.7) to 10(11.5) suckling mouse intracranial lethal doses per ml for 2 to 4 days. These levels of virus could easily infect vector mosquitoes. Mortality was high in all species of rodents except Sigmodon hispidus, adult Neotoma micropus, and adult Peromyscus leucopus. Lagomorphs were susceptible to VE infection but circulated VE virus at or near mosquito threshold levels for 1 day only. Raccoons and opossums were relatively resistant to VE infection or circulated low levels of virus in the blood. Juvenile animals of four species were more susceptible and experienced higher viremias than did adults. In two of the four, mortality was higher in the juveniles than in adults. A consideration of results obtained during this study and those of other investigators led to the conclusion that equines were of major importance, that canines, lagomorphs and rodents were of minor importance, and that other species tested were of no importance as virus amplifiers in VE epizootics.