[Isolation of influenza virus with the antigenic formula Hav4 Nav2 and Hav5 Nav2 during epizootic infection among sea gulls in the Astrakhan district in the summer of 1976].

Virological examinations of nesting colonies of Laridae birds in the avandelta of the Volga, Astrakhan region, during an epizootic in July, 1976, yielded 5 strains of influenza virus: 3 from Sterna albifrons, 1 from S. hirundo and 1 from Larus genei, identical with A/Sterna hirundo/S. Africa/61 (Hav5 Nav2) virus. At the same period two strains were isolated from Larus genei showing a previously unknown composition of the surface antigens: Hav4 Nav2. All the strains were isolated only from cloacal washings.