Clade 2.3.4.4 H5 North American highly pathogenic avian influenza viruses infect, but do not cause disease in American Black Ducks (Anas rubripes)

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

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2018
Publication Date: 6/1/2019
Citation: Spackman, E., Prosser, D., Pantin Jackwood, M.J., Stephens, C., Berlin, A. 2019. Clade 2.3.4.4 H5 North American highly pathogenic avian influenza viruses infect, but do not cause disease in American Black Ducks (Anas rubripes). Avian Diseases. 63:366–370. https://doi.org/10.1637/11950-081418-ResNote.1.
DOI: https://doi.org/10.1637/11950-081418-ResNote.1

Interpretive Summary: H5 bird flu caused the largest foreign animal disease outbreak in the US in 2014-2015 which affected over 50 million chickens and turkeys. The virus is spread by wild waterfowl, however the role of specific species is not well understood. The highest rates of detection of non-virulent forms of bird flu are often found in Mallards. American Black ducks are closely related to Mallards and will interbreed with them naturally. Therefore it was determined if American Black ducks can serve as hosts for the same strains of bird flu. It was discovered that the H5 bird flu viruses could infect American Black ducks and they can excrete virus into the environment, however the virus does not make them sick. This suggests that American Black ducks could spread the virus because they remain healthy while excreting virus into the environment.

Technical Abstract: Highly pathogenic avian influenza virus (HPAIV) from the goose/Guangdong/1996 H5 clade 2.3.4.4 lineage spread from Asia into North America in 2014, most likely by wild bird migrations. Although several variants of the virus were detected, H5N8 and H5N2 variants were the most widespread in North American wild birds and domestic poultry. In early 2015 the H5N2 virus spread through commercial poultry in the Midwest and over 50 million chickens and turkeys died or had to be culled. Related H5 HPAIVs are still endemic in much of the Eastern hemisphere. The wild bird species which were involved with dissemination of the virus in North American are not known. Dabbling ducks, especially Mallards, typically have the highest detection rates for AIVs. In order to better characterize the wild avian species which could spread the virus, American Black Ducks (Anas rubripes) (ABDU), which are closely related to Mallards, were challenged with the North American H5N2 and H5N8 index HPAIV isolates: A/Northern Pintail/WA/40964/2014 H5N2 and A/Gyrfalcon/WA/41088/2014 H5N8. Although the ABDU could be infected with low doses of both isolates (=100 50% egg infectious doses), ducks shed the H5N2 for longer than the H5N8 (10 days versus 7 days) and the titers of virus shed were higher, suggesting that ABDU could serve as a more efficient reservoir for the H5N2 virus.