There are many different subtypes of influenza A virus in wild birds, and occasionally these viruses infect poultry and ultimately humans.
It is currently unknown how influenza virus subtype diversity in wild birds evolved and how different subtypes are maintained in wild bird populations, but a recent study from the University of Georgia provides evidence that subtype diversity exists in a state of competition.
“Waterfowl especially dabbling ducks such as the Mallard are the main carriers of low pathogenic influenza A virus, and the diversity of these viruses in birds is high,” said David Stallknecht, a professor in UGA’s College of Veterinary Medicine and co-author of the study. “Yet, we know relatively little of how influenza virus subtypes interact within these bird populations.”
It is important to understand these processes because risks to domestic poultry and humans are often associated with specific subtypes such as H5 and H7 that can cause high mortality in poultry or specific strains such as the H7N9 that are associated with human disease in China.
In addition, there is fear that some of these strains may become established in migratory wild birds providing a means for global spread.
The UGA research clearly demonstrated that Mallards infected with a single influenza virus subtype develop a partial resistance to other subtypes of influenza.
“We investigated how ducks respond to influenza infection and how influenza viruses of different so-called ‘subtypes’ interact, and we found that one virus can partially protect against infections caused by other viruses of different subtypes— infections were much shorter and less virus was shed,” said Neus Latorre-Margalef, a postdoctoral student at Lund University in Sweden and lead author of the study. “This indicates that there is competition between influenza virus subtypes within duck populations.”
The results clearly demonstrate how one infection can partially protect ducks against later infections depending on how genetically similar the influenza viruses subtypes are.
These results suggest that the ability of a virus such as a highly pathogenic H5 or an H7N9 to become established in wild bird populations may be as easy as previously thought, and it is possible that such a strain would be excluded by the immunity provided by the influenza viruses that naturally circulate in these populations.
The study was performed at the College of Veterinary Medicine, The University of Georgia, Athens, GA, USA, lead by David Stallknecht together with colleagues at UGA, Neus Latorre-Margalef is an International postdoc funded by Wenner-Gren Foundations (Sweden) and the Swedish Research council.
The article “Competition between influenza A virus subtypes through heterosubtypic immunity modulates re-infection and antibody dynamics in the mallard duck” is published in PLoS Pathogens. Click here to read it.