The pathogenesis of H7 highly pathogenic avian influenza viruses in Lesser Scaup (Aythya affinis)

Authors: STEPHENS, CHRISTOPHER - Orise Fellow; PROSSER, DIANN - Us Geological Survey (USGS); Pantin Jackwood, Mary; BERLIN, ALICIA - Us Geological Survey (USGS); Spackman, Erica

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2018
Publication Date: 3/25/2019
Citation: Stephens, C.B., Prosser, D.J., Pantin Jackwood, M.J., Berlin, A.M., Spackman, E. 2019. The pathogenesis of H7 highly pathogenic avian influenza viruses in Lesser Scaup (Aythya affinis). Avian Diseases. 63(1):230-234. https://doi.org/10.1637/11909-060118-ResNote.1.
DOI: https://doi.org/10.1637/11909-060118-ResNote.1

Interpretive Summary: Bird flu can be carried by wild birds without making them sick, however little is known about which species are most important for spreading the virus. Most work has looked at dabbling ducks, therefore we evaluated whether Lesser Scaup, a North American diving duck can carry a type of bird flu called the H7 subtype. The H7 subtype is of particular interest because it can be deadly for chickens and turkeys in some virulent forms. In both 2016 and 2017 chickens and turkeys in the US were infected with H7 bird flu and resulted in substantial costs to farmers. Virus strains from each of these outbreaks was tested to see if Lesser Scaup could be infected and carry them. Both strains could infect Lesser Scaup, but caused no disease, which is consistent with the species being a carrier. However the amount of virus the Lesser Scaup excreted into the environment differed by virus strain, suggesting that they may not be able to spread each virus equally well.

Technical Abstract: Waterfowl are the natural hosts of avian influenza virus (AIV), and through migration spread the virus worldwide. Most AIVs carried by wild waterfowl are low pathogenic strains; however, Goose/Guangdong/1996 lineage clade 2.3.4.4 H5 highly pathogenic (HP) AIV now appears to be endemic in wild birds in much of the Eastern Hemisphere. Most research efforts studying AIV pathogenicity in waterfowl thus far have been directed toward dabbling ducks. In order to better understand the role of diving ducks in AIV ecology, we previously characterized the pathogenesis of clade 2.3.4.4 H5 HPAIV in lesser scaup (Aythya affinis). In an effort to further elucidate AIV infection in diving ducks, the relative susceptibility and pathogenesis of two North American lineage H7 HPAIV isolates from the most recent outbreaks in the United States was investigated. Lesser scaup were inoculated with either A/turkey/IN/1403-1/2016 H7N8 or A/chicken/TN/17-007147-2/2017 H7N9 HPAIV by the intranasal route. The approximate 50% bird infectious dose (BID50) of the H7N8 isolate was determined to be 103 50% egg infectious doses (EID50), and the BID50 of the H7N9 isolate was determined to be <102 EID50, indicating some variation in adaptation between the two isolates. No mortality or clinical disease was observed in either group except for elevated body temperatures at 2 and 4 days postinoculation (DPI). Virus shedding was detected up to 14 DPI from both groups, and there was a trend for shedding to have a longer duration and at higher titer levels from the cloacal route. These results demonstrate that lesser scaup are susceptible to both H7 lineages of HPAIV, and similar to dabbling duck species, they shed virus for long periods relative to gallinaceous birds and don't present with clinical disease.