Evidence released this week suggests that highly pathogenic flu viruses, similar to the H5 avian influenza virus that devastated US farms in 2014/5 do not persist in wild birds.
The research, led by St Jude Children’s Research Hospital, found that, while wild ducks and other aquatic birds are known to be natural hosts for low pathogenic flu viruses associated with milder symptoms, this is not the case with highly pathogenic viruses.
Author Robert Webster said the findings provide a scientific basis for the decision by officials to use culling and quarantines to stop the 2014/5 outbreak in poultry. But that research was needed to identify the mechanism that had evolved in the wild birds to disrupt the perpetuation of highly pathogenic influenza.
In the study, published in the Proceedings of the National Academy of Sciences, researchers analysed throat swabs and other biological samples taken from more than 22,000 wild ducks and other aquatic birds, collected before, during and after a 2014/5 H5 flu outbreak in poultry.
The outbreak was linked to a highly pathogenic H5N8 influenza A virus spread from Asia to North America by migratory waterfowl. The H5N8 virus reasserted, or mixed genes, with other influenza viruses in North American waterfowl and went to trigger 248 flu outbreaks in commercial and backyard flocks in the US and Canada at a cost of nearly $5bn.
Officials worked to end the outbreaks by quarantining and eliminating infected poultry, with the last case reported in June 2015. They were worried that the highly pathogenic virus would be re-introduced into poultry farms by migratory aquatic birds carrying the virus.
But none of the migratory birds included in this analysis in Canada, the Mississippi flyway and along the Atlantic coast were infected with highly pathogenic flu virus. The sampling work was carried out by researchers from the University of Georgia, Ohio State University and funded by the Centres of Excellence for Influenza Research and Surveillance
Professor Webster said such viruses had not been identified in any of the more than 100,000 wild birds tested since the flu surveillance sampling began 43 years ago.
“Existing immunity in wild birds is one of the possible explanations that may explain why highly pathogenic influenza A viruses do not become established in wild bird populations.
“But a more complete understanding of the mechanisms at work would aid efforts to prevent, control and eradicate these dangerous viruses involved in poultry in other parts of the world,” he added.