Evidence of infection by H5N2 highly pathogenic avian influenza viruses in healthy wild waterfowl

Abstract

The potential existence of a wild bird reservoir for highly pathogenic avian influenza (HPAI) has been recently questioned by the spread and the persisting circulation of H5N1 HPAI viruses, responsible for concurrent outbreaks in migratory and domestic birds over Asia, Europe, and Africa. During a large-scale surveillance programme over Eastern Europe, the Middle East, and Africa, we detected avian influenza viruses of H5N2 subtype with a highly pathogenic (HP) viral genotype in healthy birds of two wild waterfowl species sampled in Nigeria. We monitored the survival and regional movements of one of the infected birds through satellite telemetry, providing a rare evidence of a non-lethal natural infection by an HP viral genotype in wild birds. Phylogenetic analysis of the H5N2 viruses revealed close genetic relationships with H5 viruses of low pathogenicity circulating in Eurasian wild and domestic ducks. In addition, genetic analysis did not reveal known gallinaceous poultry adaptive mutations, suggesting that the emergence of HP strains could have taken place in either wild or domestic ducks or in non-gallinaceous species. The presence of coexisting but genetically distinguishable avian influenza viruses with an HP viral genotype in two cohabiting species of wild waterfowl, with evidence of non-lethal infection at least in one species and without evidence of prior extensive circulation of the virus in domestic poultry, suggest that some strains with a potential high pathogenicity for poultry could be maintained in a community of wild waterfowl.

Figure 1. Movement paths of one White-faced Whistling Duck (Dendrocygna viduata) fitted with a satellite transmitter, from Hadejia-Nguru Wetlands in northern Nigeria to Lake Chad in western Chad, during February–March 2007.

Dates and minimum distances between main staging areas (orange circles) are indicated on the satellite image.

Figure 2. Phylogenetic tree based on the sequence analysis of the entire segment encoding for HA proteins, with representative H5N1, H5N2, and H5N3 influenza A viruses isolated in naturally infected wild and domestic birds in Asia, Europe, and Africa.

Viral sequences analyzed in this study are marked with a circle.

Figure 3. Phylogenetic tree based on the sequence analysis of the entire segment encoding for NA proteins.

The phylogenetic tree includes selected N2 sequences of influenza viruses isolated in Asia, Europe and Africa. Viral sequences analyzed in this study are marked with a circle.