While wild ducks and other aquatic birds are known to be natural hosts for low pathogenic flu viruses associated with milder symptoms, the results of this study indicate that is not the case with the highly pathogenic flu viruses that are associated with more severe illness.

In this study, researchers analysed samples taken from 22,892 wild ducks and other aquatic birds collected before, during and after a 2014-15 H5 flu outbreak in poultry.

The outbreak has been linked to a highly pathogenic H5N8 influenza A virus spread from Asia to North America by migratory waterfowl, which after mixing genes with other viruses went on to trigger 248 flu outbreaks in commercial and backyard turkey and poultry farms in the US and Canada at a cost of nearly $5 billion.

Officials 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 were infected with a highly pathogenic flu virus.

Such viruses have not been identified in any of the more than 100,000 wild birds tested since the flu surveillance sampling began 43 years ago, according to corresponding author Robert Webster, PhD, an emeritus member of the St. Jude Department of Infectious Diseases.

“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,” he said.

“But a more complete understanding of the mechanisms at work would aid efforts to prevent, control and eradicate these dangerous viruses in poultry in other areas of the world.”

St. Jude Children’s Research Hospital led the research, which appears online this week in the journal Proceedings of the National Academy of Sciences.