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

Abstract

Highly pathogenic avian influenza virus (HPAIV) from the goose/Guangdong/1996 clade 2.3.4.4 H5 lineage spread from Asia into North America in 2014, most likely by wild bird migrations. Although several variants of the virus were detected, an H5N8 and H5N2 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 America 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 (≤102 50% egg infectious doses), ducks shed the H5N2 longer than the H5N8 (10 days versus 7 days) and the titers of virus shed were higher. Although there were too few ducks available on which to draw definitive conclusions, this suggests that ABDU could serve as a more efficient reservoir for the H5N2 virus.