Louping-ill encephalomyelitis in the sheep: VI. Infection of the 120-day foetus

Exposure of the 120-day sheep foetus to louping-ill virus resulted in generalized infection of neurons, severe neuropathological changes and death. Virus was detected in the cerebrospinal fluid as early as 2 days after intravenous inoculation. Levels of viraemia were generally low and few cells in lymphoid tissue synthesized viral antigen. Immunologically the foetus was competent to louping-ill virus in that neutralizing antibody, initially IgM and later IgG, was found in serum from 4 days after inoculation. Haemagglutination inhibiting antibody was, however, not detected at any stage. Non-specific neutralizing substances occurred in all sera from infected and control animals. Cells containing globulins were present in lymphoid tissue from every case, including the controls. Early inflammatory foci in nervous tissue consisted largely of polymorphonuclear cells. Immuno-globulins could not be demonstrated in perivascular inflammatory cells at any stage.