Widespread detection of highly pathogenic H5 influenza viruses in wild birds from the Pacific Flyway of the United States

Abstract

A novel highly pathogenic avian influenza virus belonging to the H5 clade 2.3.4.4 variant viruses was detected in North America in late 2014. Motivated by the identification of these viruses in domestic poultry in Canada, an intensive study was initiated to conduct highly pathogenic avian influenza surveillance in wild birds in the Pacific Flyway of the United States. A total of 4,729 hunter-harvested wild birds were sampled and highly pathogenic avian influenza virus was detected in 1.3% (n = 63). Three H5 clade 2.3.4.4 subtypes were isolated from wild birds, H5N2, H5N8, and H5N1, representing the wholly Eurasian lineage H5N8 and two novel reassortant viruses. Testing of 150 additional wild birds during avian morbidity and mortality investigations in Washington yielded 10 (6.7%) additional highly pathogenic avian influenza isolates (H5N8 = 3 and H5N2 = 7). The geographically widespread detection of these viruses in apparently healthy wild waterfowl suggest that the H5 clade 2.3.4.4 variant viruses may behave similarly in this taxonomic group whereby many waterfowl species are susceptible to infection but do not demonstrate obvious clinical disease. Despite these findings in wild waterfowl, mortality has been documented for some wild bird species and losses in US domestic poultry during the first half of 2015 were unprecedented.

Changes in adaptation of H5N2 highly pathogenic avian influenza H5 clade 2.3.4.4 viruses in chickens and mallards

“…In late 2014 and early 2015, this H5N2 virus caused outbreaks in turkey and chicken commercial operations in British Columbia, Canada (24). In the Pacific Flyway, this virus was commonly detected in wild waterfowl species, mostly in mallards and American wigeons ( Anas Americana ), but also in Northern pintails ( Anas acuta ), Wood ducks ( Aix sponsa ), Northern shovelers ( Anas clypeata ), Canada geese ( Anas clypeata ), American green-winged teal ( Anas carolinensis ), Gadwall ( Anas stepera ), and Cinnamon teal ( Anas Cyanoptera ) (32, 2, 6), and was also detected in backyard poultry in the U.S. (7, 30). Subsequently, the H5N2 virus was detected in Midwestern U.S., causing the devastating outbreak in commercial poultry in from March to June of 2015.…”

“…In early 2014, outbreaks of H5N8 HPAI were reported in South Korea and Japan in poultry and wild aquatic birds (17), with migratory aquatic birds highly suspected in playing a key role in the spread of the virus (9). In late autumn of 2014 and early 2015, H5N8 HPAI viruses were detected in Russia and several countries in Europe, and in captive falcons, wild birds, and backyard aquatic and gallinaceous poultry in the Western U.S. (2, 8, 15, 33). In addition, another novel reassortant HPAI virus of H5 clade 2.3.4.4, an H5N2, was identified as the cause of an outbreak in poultry farms in British Columbia (24) and was subsequently detected in the U.S. in wild waterfowl and backyard poultry (2, 7, 31).…”

“…In late autumn of 2014 and early 2015, H5N8 HPAI viruses were detected in Russia and several countries in Europe, and in captive falcons, wild birds, and backyard aquatic and gallinaceous poultry in the Western U.S. (2, 8, 15, 33). In addition, another novel reassortant HPAI virus of H5 clade 2.3.4.4, an H5N2, was identified as the cause of an outbreak in poultry farms in British Columbia (24) and was subsequently detected in the U.S. in wild waterfowl and backyard poultry (2, 7, 31). From March through mid-June of 2015, H5N2 viruses caused widespread HPAI infections in commercial poultry flocks in the upper Midwestern U.S. states (10).…”

Reassortment of Influenza A Viruses in Wild Birds in Alaska before H5 Clade 2.3.4.4 Outbreaks

“…HPAI H5N2 became the most widespread in US poultry, prompting the culling of ≈49 million chickens and turkeys in 15 states ( 4 ). During the outbreaks (November 2014–December 2015), surveillance efforts increased; consequently, later stages of the epidemic were better characterized ( 5 , 6 ) relative to the beginning. Analysis of wild bird viruses from Alaska preceding outbreaks remains one of the few avenues for elucidating how H5N8 entered and reassorted with North American lineage viruses.…”

Surveillance for highly pathogenic H5 avian influenza virus in synanthropic wildlife associated with poultry farms during an acute outbreak

“…Surveillance efforts continued to identify the Eurasian H5 icA viruses in wild birds in a number of western states (Washington, Oregon, California, Utah, Idaho)4 and less than two months after the first detection in the US, H5N8 HPAIV was detected in a commercial turkey flock in California, followed by a second detection in a commercial chicken flock approximately three weeks later. Just over two weeks after that, and in what was to be the first of more than one hundred affected premises in the state, the reassortant EU/AM H5N2 HPAIV was detected in a commercial turkey farm in Minnesota1.…”