Evidence for the contribution of the host species to the extent of antigenic variation of N1 influenza virus neuraminidase.

N1 influenza virus neuraminidases (NA) derived from avian, swine and human virus isolates, including the genetically related classic strains A/FPV/Rostock/34, A/Swine/1976/31, A/PR8/34 and A/FM1/47, were analysed serologically by neuraminidase inhibition (NI), inhibition of virus release (IVR) and competitive radio-immunoassays (competitive RIA). Comparing the three tests, competitive RIA appeared to be more reliable than NI and IVR for a quantitative assessment of antigenic relatedness. Together with evidence presented by others, these studies indicate that the host species contributes to the extent of antigenic variation of NAses. In contrast to NAses of human viruses where antigenic drift occurs readily, NAses of animal influenza viruses, from birds or mammalians, undergo far fewer antigen changes.