Sep. 11, 2013 — Ducks and gulls are the natural hosts of influenza A virus. Ragnhild Tønnessen's PhD research project has characterised influenza A viruses in gulls and ducks in Norway. Her discoveries may lead to a better understanding of the epidemiology and host adaptation of influenza A virus.
Wild birds, particularly ducks and gulls, are the natural hosts for influenza A viruses which can cause disease in animals and humans. Influenza A viruses can be divided into subtypes, of which the majority have been found in wild birds. Most subtypes of influenza A virus cause subclinical infections in wild birds. Infections in domestic chickens most commonly result in mild disease. In rare cases, if introduced from wild birds to poultry, some viruses of the H5 and H7 subtypes mutate and become highly pathogenic. One example of this is the highly pathogenic H5N1 virus in Southeast Asia known to cause “bird flu”.
Due to the outbreak of highly pathogenic avian influenza virus subtype H5N1 in Southeast Asia, a programme to monitor influenza viruses in wild birds in Norway was initiated in 2005. A large number of samples, gathered by hunters from ducks and gulls, were analysed at the Norwegian Veterinary Institute. Samples collected from Rogaland County in the South-West of Norway during the hunting seasons (August-December) of 2005-2007 and 2009-2010 were studied. The results showed that low pathogenic avian influenza viruses were present in 15.5% of the samples, and that the virus occurrence was higher in dabbling ducks than in gulls. The virus prevalence was lowest in December. Many different subtypes of the influenza A virus were detected, but not the highly pathogenic H5N1 virus.