Molecular and biological properties of a variant of avian influenza A/Seal/Massachusetts/1/80 (H7N7) virus that is pathogenic for mice.

A/Seal/Mass/80 influenza virus has been shown to be closely related antigenically and genetically to avian influenza H7N7 viruses, however, the virus does not replicate efficiently in avian species but does replicate in most mammals, except mice (Hinshaw et al., Infect. Immun., 34, 351-361, 1981). In order to develop a model defining the molecular changes that occur during acquisition of virulence, the A/Seal/Mass/80 virus was adapted to growth in mouse lungs. The adaptation was accompanied by changes in a number of properties of the haemagglutinin as well as by changes in other genes of the virus as determined by RNA: RNA hybridization.