Pathogenicity, immunogenicity and genetic stability in mice and ferrets of a cold inhibitor-resistant mutant of influenza H3N2 virus.

A cold inhibitor-resistant mutant was derived from MRC-2 virus by means of serial passages in the presence of rabbit serum and at gradually decreasing temperatures. This virus, denoted MRC-2 IRc, grew well at both 26 and 37 degree C. The pathogenicity and immunogenicity of the virus was examined in mice and ferrets. No clinical reactions were detected in either species. Both mice and ferrets developed high levels of hemagglutination inhibition and neuraminidase inhibition antibodies. The virus was reisolated from the lungs of intranasally inoculated mice; in ferrets it was recovered from nasal washing and trachea but not from lungs. The properties of the isolated viruses were examined. The viruses reisolated from mice lost their reproductive capacity at 26 degree C and were less resistant to inhibitors than the original virus. The virus isolated from the ferret nose was identical with the original virus, however the tracheal isolate exhibited a certain degree of reversion in both the markers tested.