Isolation of influenza viruses from wild birds in the Volga River basin and in the North Caspian Region

Background: The North Caspian Region and delta of the Volga River constitute historic flyways and a place of mass congregation of wild birds for most of the year. Methods: A total 3513 biological samples from 3229 birds of 37 species were collected, antigenic structure and receptor activity of isolated influenza A viruses were studied. Nucleotide sequences of NS gene PCR fragments were analysed. Results: 344 strains of influenza A virus with various combination of hemagglutinin and neuraminidase were isolated: H4N3, H4N6, H5N2,H6N2, H9N2, H13N3, H13N6, H13N8, H14N5, H14N6. The influenza virus A/H13 was isolated annually from the nestlings of Larus ichthyaetus and L. argentatus species. Isolation of viruses from embryos and young birds suggests the existence of at least two ways of infection: alimentary and transovarial. The studies of the binding of the viruses H13 and H14 with gangliosides GM3, GD1a and 3SPG did not reveal the essential difference from the viruses of H1-H12 subtypes. Among avian HA only HA13 subtype has the substitution at residue 77 DT, A and 228 GS. The substitution 225 GN found in HA 14 virus also isolated only in the North of Caspian Sea. Study of NS genes of some isolates revealed significant differences in the structure of genes of influenza viruses isolated at the same time but from various species of birds. Conclusions: The ability of the viruses H5, H4, H6, H9 to infect mammals and to provoke epizootics determine the necessity to carry out further monitoring in the Northern Caspian basin and other key points in Northern Eurasia. (C) 2001 Elsevier Science B.V. All rights reserved.