In Semliki Forest virus encephalitis, antibody rapidly clears infectious virus and is required to eliminate viral material from the brain, but is not required to generate lesions of demyelination.

Semliki Forest virus (SFV) infection of the laboratory mouse provides a well-characterized tractable system to study the pathogenesis of virus encephalitis and virus induced demyelination. In microMT mice, which have no antibodies, infectious virus persisted in both the serum and the brain for several weeks, indicating that antibodies are required to eliminate infectious virus. In immunocompetent mice, virus infectivity in the brain was undetectable after the first week of infection, but virus RNA levels declined slowly. Following SFV infection, lesions of demyelination were present in the brains of both immunocompetent and microMT mice, indicating that antibodies are not required to generate lesions of demyelination.