A mouse hepatotropic variant of influenza virus.

A hepatotropic variant of avian influenza virus A/Turkey/England 63 (Hav 1, Nav 3) was selected by serial passages in mouse liver. Adaptation to this organ was established after 13 in vivo passages and was found to improve during further passages as shown by increasing rates of replication in livers of ICR mice. The mutant virus finally selected was stable and differed from the original virus mainly in lethality upon intraperitoneal injection in mice, in its ability to grow to high titers in livers of susceptible animals and in plaque morphology in chick embryo fibroblasts. No differences were detected in hemagglutination inhibition and neutralization by standard mouse antisera. Pathogenicity for the liver was independent of the route of inoculation, included other laboratory animals sensitive to influenza virus and could be inhibited by amantadine. Fatal hepatitis in 50 per cent of susceptible mice by the intraperitoneal route required from 10 to 20 EID50-. Pathological changes consisted of severe necrosis of liver parenchyma accompanied by release of F antigen into the serum and were apparently due to virus replication in hepatic cells as evidenced by immunofluorescence. The main implications of this animal model for studies on experimental hepatitis and on myxovirus-host interactions in an organ not usually associated with influenza are discussed.