Isolation from birds of influenza viruses with human neuraminidase.

Attempts at virus isolation from cloacal swabs resulted in the recovery of 10 strains of hemagglutinating viruses from a total of 349 ducks, mainly shelducks (Tadorna tadorna) captured in the north of France. Four of these isolates were identified as influenza strains corresponding to the following antigenic composition: Hav6-N2, Hav6-Nav4 and Hav1-N2 (2 strains). Shelduck is known to be a partially migratory species, wintering in western Europe, some of them migrating northward to Scandinavia during the summer. The captures were made between November 1976 and February 1977: one of the birds was caught four times and was found to be negative for virus in November, positive in December (isolation of a strain Hav6-Nav4), negative again in January and February. Blood taken in February did not show the presence of HI antibodies to the homologous virus.