Susceptibility of common family Anatidae bird species to clade H5N6 high pathogenicity avian influenza virus: an experimental infection study

Background: There were large outbreaks of high pathogenicity avian influenza (HPAI) caused by clade H5N6 viruses in the winter of 2016-2017 in Japan, which caused large numbers of deaths among several endangered bird species including cranes, raptors, and birds in Family Anatidae. In this study, susceptibility of common Anatidae to a clade H5N6 HPAI virus was assessed to evaluate their potential to be a source of infection for other birds. Eurasian wigeons (Mareca penelope), mallards (Anas platyrhynchos), and Northern pintails (Anas acuta) were intranasally inoculated with 106, 104, or 102 50% egg infectious dose (EID50) of clade A/teal/Tottori/1/2016 (H5N6).

Results: All birds survived for 10 days without showing any clinical signs of infection. Most ducks inoculated with ≥ 104 EID50 of virus seroconverted within 10 days post-inoculation (dpi). Virus was mainly shed via the oral route for a maximum of 10 days, followed by cloacal route in late phase of infection. Virus remained in the pancreas of some ducks at 10 dpi. Viremia was observed in some ducks euthanized at 3 dpi, and ≤ 106.3 EID50 of virus was recovered from systemic tissues and swab samples including eyeballs and conjunctival swabs.

Conclusions: These results indicate that the subject duck species have a potential to be a source of infection of clade HPAI virus to the environment and other birds sharing their habitats. Captive ducks should be reared under isolated or separated circumstances during the HPAI epidemic season to prevent infection and further viral dissemination.