After HPAI H5 arrived to North America in the fall of 2014, and went on to spark the largest epizootic outbreak in U.S. history during the spring of 2015, the expectation was it would return with a vengeance the following fall.
Not only did that not happen, the virus has literally disappeared from wild and migratory birds sampled in North America since the summer of 2015.
The surprise finding by researchers, published in PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl earlier this summer, is that while migratory waterfowl can briefly carry HPAI H5, they are not a long-term reservoir for highly pathogenic avian flu viruses.
HPAI viruses appear to burn out fairly quickly in aquatic waterfowl populations, likely due to their immunity to LPAI viruses, and would have to be reintroduced periodically.
Another study, published earlier this month in Sci Repts.: Southward Autumn Migration Of Waterfowl Facilitates Transmission Of HPAI H5N1, suggests that waterfowl pick up new HPAI viruses in the spring (likely from poultry or terrestrial birds) on their way north to their summer breeding spots.
The following fall enough of the virus may still be circulating among them - due in part to immunologically naive hatchlings born over the summer - to be spread during their southbound migration.
At least, that's the current thinking. There are still huge gaps in our understanding of the ecology of avian flu in migratory birds, and so none of this is writ in stone.
Which brings us to a new report, released late Friday afternoon by APHIS, which announces the detection of a lone mallard from Alaska which tested positive for HPAI H5N2 earlier this month.
This is the first detection of HPAI in North America since the summer of 2015 - and while one duck does not a harbinger make - it does raise the possibility that HPAI has been reintroduced into North American waterfowl.
First the USDA press release, then I'll return with a bit more.
USDA Confirms Highly Pathogenic H5N2 Avian Influenza in a Wild Mallard Duck in Alaska
Published: Aug 26, 2016
The United States Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) has confirmed the presence of highly pathogenic H5N2 avian influenza (HPAI) in a wild mallard duck from a state wildlife refuge near Fairbanks, Alaska. CDC considers the risk to the general public from these HPAI H5 infections to be low. No human infections with Eurasian H5 viruses have occurred in the United States. As a reminder, the proper handling and cooking of poultry and eggs to an internal temperature of 165 ˚F kills bacteria and viruses, including HPAI.
H5N2 HPAI has NOT been found in the U.S. – in either wild or commercial birds – since June 2015. However, anyone involved with poultry production from the small backyard to the large commercial producer should review their biosecurity activities to assure the health of their birds. To facilitate such a review, a biosecurity self-assessment and educational materials can be found at http://www.uspoultry.org/animal_husbandry/intro.cfm
The United States has the strongest AI surveillance program in the world, and USDA is working with its partners to actively look for the disease in commercial poultry operations, live bird markets and in migratory wild bird populations. The wild mallard duck was captured and a sample tested as part of ongoing wild bird surveillance. Since July 1, 2016, USDA and its partners have tested approximately 4,000 samples, with a goal to collect approximately 30,000 samples before July 1, 2017. Approximately 45,500 samples were tested during wild bird surveillance from July 1, 2015-June 30, 2016.
Since wild birds can be infected with these viruses without appearing sick, people should minimize direct contact with wild birds by using gloves. If contact occurs, wash your hands with soap and water and change clothing before having any contact with healthy domestic poultry and birds. Hunters should dress game birds in the field whenever possible and practice good biosecurity to prevent any potential disease spread. Biosecurity information is available at: https://www.aphis.usda.gov/publications/animal_health/2015/fsc_hpai_hunters.pdf
In addition to practicing good biosecurity, all bird owners should prevent contact between their birds and wild birds and report sick birds or unusual bird deaths to State/Federal officials, either through their state veterinarian or through USDA’s toll-free number at 1-866-536-7593. Additional information on biosecurity for backyard flocks can be found at http://healthybirds.aphis.usda.gov.
Avian influenza (AI) is caused by an influenza type A virus which can infect poultry (such as chickens, turkeys, pheasants, quail, domestic ducks, geese and guinea fowl) and is carried by free flying waterfowl such as ducks, geese and shorebirds. AI viruses are classified by a combination of two groups of proteins: hemagglutinin or “H” proteins, of which there are 16 (H1–H16), and neuraminidase or “N” proteins, of which there are 9 (N1–N9). Many different combinations of “H” and “N” proteins are possible. Each combination is considered a different subtype, and can be further broken down into different strains. AI viruses are further classified by their pathogenicity (low or high)— the ability of a particular virus strain to produce disease in domestic chickens.
Alaska's Arctic Refuge, where more than 200 bird species spend their summers, serves as a central hub, and funnels migratory birds south via all four North American Flyways.
Over the next couple of months wild bird surveillance will ramp up in the lower 48, and we'll hopefully get a better idea whether this HPAI detection in Alaska is a fluke or a trend.