Multiplication of virulent and demyelinating Semliki Forest virus in the mouse central nervous system: consequences in BALB/c and SJL mice.

The sites of multiplication in the mouse central nervous system (CNS) of the virulent L10 strain of Semliki Forest virus (SFV) and the L10-SFV-derived demyelinating M9 mutant were determined using both BALB/c and SJL mouse strains. In situ hybridization (ISH), using a cRNA probe to an SFV non-structural sequence, and immunogold-silver staining (IGSS), using polyclonal anti-SFV rabbit IgG, were the techniques utilized. For L10-SFV, viral RNA and antigen were detected in neurons and glial cells of both mouse strains. For BALB/c mice infected with M9-SFV, both neuronal and glial cell infection was less extensive than that obtained with L10. ISH or IGSS were generally not sensitive enough to detect viral RNA and antigen, respectively, in M9-SFV-infected SJL mice. M9-SFV multiplied to a similar titre in primary cultures of glial cells derived from either BALB/c or SJL mice. Following infection with M9-SFV, small plaques of demyelination in the CNS and occasional small aggregates of mononuclear leukocytes in the leptomeninges persisted for up to 12 months in SJL mice but not BALB/c mice. This was not associated with detectable persistence of infectious virus, viral antigen or viral RNA in the CNS.