Pathogenicity in chickens and turkeys of a 2021 United States H5N1 highly pathogenic avian influenza clade 2.3.4.4b wild bird virus compared to two previous H5N8 clade 2.3.4.4 viruses

Authors: Pantin Jackwood, Mary; Spackman, Erica; LEYSON, CHRISTINA - Orise Fellow; YOUK, SUNGSU - Orise Fellow; Lee, Scott; Moon, Linda; TORCHETTI, MIA - Animal And Plant Health Inspection Service (APHIS); KILLIAN, MARY - Animal And Plant Health Inspection Service (APHIS); LENOCH, JULIANNA - Animal And Plant Health Inspection Service (APHIS); Kapczynski, Darrell; Swayne, David; Suarez, David

Submitted to: Viruses
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2023
Publication Date: 11/18/2023
Citation: Pantin Jackwood, M.J., Spackman, E., Leyson, C., Youk, S., Lee, S.A., Moon, L.M., Torchetti, M.K., Killian, M.L., Lenoch, J.B., Kapczynski, D.R., Swayne, D.E., Suarez, D.L. 2023. Pathogenicity in chickens and turkeys of a 2021 United States H5N1 highly pathogenic avian influenza clade 2.3.4.4b wild bird virus compared to two previous H5N8 clade 2.3.4.4 viruses. Viruses. 15(11):2273. https://doi.org/10.3390/v15112273.
DOI: https://doi.org/10.3390/v15112273

Interpretive Summary: Highly pathogenic avian influenza viruses of the subtype H5N1 clade 2.3.4.4 are a major threat to poultry and are spread by wild birds. This virus was detected in wild waterfowl in the United States in December of 2021 and since then has spread to domestic birds and many wild bird species in most states. We conducted experiments to study the disease this virus causes in chickens and turkeys, and found that the virus was more infectious in turkeys than chickens. Two other clade 2.3.4.4 viruses were also examined. A virus from 2016 was similarly infections for chickens and turkeys; however, a 2014 virus was more infectious in turkeys than in chickens. Regardless of the virus, turkeys took longer to die increasing the number of days the virus was being excreted, which, in addition to the higher infectivity, could explain why the viruses transmitted well in turkeys but not in chickens. This information helps us understand the epidemiology of this virus so it can be better controlled.

Technical Abstract: Highly pathogenic avian influenza viruses (HPAIVs) of subtype H5 of the Gs/GD/96 lineage remain a major threat to poultry due to endemicity in wild birds. H5N1 HPAIVs from this lineage were detected in 2021 in the United States (U.S.) and since then have infected many wild and domestic birds. We evaluated the pathobiology of an early U.S. H5N1 HPAIV (clade 2.3.4.4b, 2021) and two H5N8 HPAIVs from previous outbreaks in the U.S. (clade 2.3.4.4c, 2014) and Europe (clade 2.3.4.4b, 2016) in chickens and turkeys. Differences in clinical signs, mean death times (MDTs), and virus transmissibility were found between chickens and turkeys. The mean bird infective dose (BID50) of the 2021 H5N1 virus was approximately 2.6 log10 50% embryo infective dose (EID50) in chickens and 2.2 log10 EID50 in turkeys, and the virus transmitted to contact-exposed turkeys but not chickens. The BID50 for the 2016 H5N8 virus was also slightly different in chickens and turkeys (4.2 and 4.7 log10 EID50, respectively); however, the BID50 for the 2014 H5N8 virus was higher for chickens than turkeys (3.9 and approximately 0.9 log10 EID50, respectively). With all viruses, turkeys took longer to die (MDTs of 2.6–8.2 days for turkeys and 1–4 days for chickens), which increased the virus shedding period and facilitated transmission to contacts.