Mouse encephalitis induced by avirulent Semliki forest virus.

Encephalitis caused by avirulent Semliki Forest virus was studied at regular intervals for 6 weeks in experimentally infected mice. The most obvious lesion was perivascular cuffing. Microglia were predominant near the vessels early in the infection. The cells of the cuffs were mostly lymphocytes. Although the virus produced acute encephalitis, which gradually resolved by 6 weeks, at no time were there abnormal neurological clinical signs. The cells of the brain and the immune response reacted to eliminate the virus.