Recent research led by St. Jude Children’s Research Hospital sought to understand why, leading up to and following the 2014-2015 outbreak of Highly Pathogenic Avian Influenza (HPAI), the HPAI virus was not found in wild bird populations in North America.
Wild waterfowl are recognized as carriers for the Low Pathogenic Avian Influenza (LPAI) virus, which manifest with mild or no symptoms in waterfowl. HPAI viruses result in significantly more severe symptoms that are often fatal for poultry including lethargy, nasal discharge, difficulty breathing, and neurological symptoms.
Research during the outbreaks indicated that the highly pathogenic H5N8 strain of the virus had originated in Asia and had been spread to North America by migratory waterfowl. This strain, in combining with circulating wild viruses in North America, led to the devastating H5 HPAI outbreaks in the United States poultry industry.
In order to understand the composition of the avian influenza virus in wild bird populations, the research group studied 22,892 wild bird samples collected prior to the 2014-2015 outbreaks, during the outbreak investigations, and following the outbreaks. The researchers additionally examined 100,000 historical wild bird surveillance samples from the past 43 years.
The research team’s results were surprising: in the 43 years leading up to the 2014-2015 HPAI outbreaks, no HPAI viruses had been detected in North American wild birds, and no subsequent HPAI viruses have been detected in wild birds since June 11, 2015. Though the United States’ “stamping out” policy for infected domestic poultry helped to eradicate HPAI in those flocks, the results led the researchers to question whether there are inherent mechanisms that limit the existence and spread of HPAI viruses in wild waterfowl and bird populations.
The research team speculates that several factors may contribute to the lack of HPAI persistence in wild waterfowl and bird populations, including but not limited to: strict biosecurity and stamping out policies on poultry farms; pre-existing immunity to many LPAI viruses; population immunity interactions; and, natural genetic resistance to disease from HPAI.
The researchers said that additional surveillance and research will be needed to fully document and understand the mechanisms of HPAI resistance in wild waterfowl. A link to the complete article is available here.
