Infectivity, transmission and pathogenicity of H5 highly pathogenic avian influenza clade 2.3.4.4 (H5N8 and H5N2) United States index viruses in Pekin ducks and Chinese geese

Authors: Pantin Jackwood, Mary; COSTA-HURTADO, MAR - Consultant; BERTRAN, KATERI - Consultant; DeJesus, Eric; Smith, Diane; Swayne, David

Submitted to: Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2017
Publication Date: 6/9/2017
Citation: Pantin Jackwood, M.J., Costa-Hurtado, M., Bertran, K., Dejesus, E.G., Smith, D.M., Swayne, D.E. 2017. Infectivity, transmission and pathogenicity of H5 highly pathogenic avian influenza clade 2.3.4.4 (H5N8 and H5N2) United States index viruses in Pekin ducks and Chinese geese. Veterinary Research. 48(1):33. doi:10.1186/s13567-017-0435-4.

Interpretive Summary: In 2014-2015, H5N8 and H5N2 highly pathogenic avian influenza (HPAI) viruses, clade 2.3.4.4, caused a devastating outbreak in poultry in the United States. Initially, the viruses were detected in wild waterfowl and backyard birds, and later in commercial poultry. Since domestic waterfowl are common backyard poultry frequently in contact with wild waterfowl, the infectivity, transmissibility, and pathogenicity of these H5 HPAI viruses was investigated in domestic ducks and geese. Pekin ducks infected with the viruses showed no or mild clinical signs. Most infected geese only had mild clinical signs, but several geese presented severe neurological signs and had to be euthanized. Pekin ducks also shed lower titers of virus and for a shorter period of time than geese. In conclusion, the H5 HPAI viruses can infect domestic waterfowl and easily transmit to contact birds, with geese being more susceptible to infection than ducks. The infected birds shed virus for several days, representing a risk to other poultry species.

Technical Abstract: In late 2014, a H5N8 highly pathogenic avian influenza (HPAI) virus, clade 2.3.4.4, spread by migratory birds into North America mixing with low pathogenicity AI viruses to produce a H5N2 HPAI virus. The H5N8 and H5N2 HPAI viruses were detected initially in wild waterfowl and backyard birds, and later in commercial poultry. Since domestic waterfowl are common backyard poultry frequently in contact with wild waterfowl, the infectivity, transmissibility, and pathogenicity of these H5 HPAI viruses was investigated in domestic ducks and geese. Two-week-old Pekin ducks and Chinese geese were inoculated with the two United States H5 index viruses: A/Gyrfalcon/Washington/40188-6/2014 (H5N8) and A/Northern Pintail/Washington/40964/2014 (H5N2). Pekin ducks infected with the viruses had an increase in body temperature but no or mild clinical signs, only some ducks presenting mild ataxia. Infected geese did not show increases in body temperature and most only had mild clinical signs. However, several geese presented neurological signs some severe enough that had to be euthanized. Pekin ducks also shed lower titers of virus and for a shorter period of time than geese. Pekin ducks became infected and transmitted the viruses to contacts when inoculated with high virus doses [(10^4 and 10^6 50% embryo infective dose (EID50)], but not with a lower dose (10^2 EID50). Geese inoculated with the H5N8 virus became infected regardless of the virus dose given, and transmitted the virus to direct contacts. Only geese inoculated with the higher doses of the H5N2 virus (10^4 and 10^6 EID50) and their contacts became infected, indicating differences in infectivity between the two index viruses and the two waterfowl species. In conclusion, the H5 HPAI viruses can infect domestic waterfowl and easily transmit to contact birds, with geese being more susceptible to infection than ducks. The disease is mostly asymptomatic, but infected birds shed virus for several days, representing a risk to other poultry species.