Detection of viral-specific nucleic acid and intracellular virions in ventral horn neurons of lactate dehydrogenase-elevating virus infected C58 mice

C58 mice which have been immunosuppressed by treatment with cyclophosphamide (200 mg/kg) one day prior to infection with the C strain of lactate dehydrogenase-elevating virus (LDV-C) develop poliomyelitis. Using in situ hybridisation, we found that some ventral horn neurons in these mice contain cytoplasmic viral-specific nucleic acid. Viral-specific nucleic acid was also found within a few small cells located near inflammatory foci. In addition, mature virus particles were observed by electron microscopy in some ventral horn neurons, indicating that these cells are productively infected in C58 mice. Neither viral nucleic acid nor virions were found in the ventral horn neurons of poliomyelitis-resistant mouse strains or C58 mice that were not immunosuppressed prior to infection. Ventral horn neurons which contained viral nucleic acid or virions within cytoplasmic vesicles generally were normal in appearance and were not located within poliomyelitis inflammatory foci. Our data are consistent with the hypothesis that infected neurons first replicate virus and subsequently are attacked and cleared by inflammatory cells.