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ARS Home » Southeast Area » Athens, Georgia » U.S. National Poultry Research Center » Exotic & Emerging Avian Viral Diseases Research » Research » Publications at this Location » Publication #353920

Research Project: Intervention Strategies to Prevent and Control Disease Outbreaks Caused by Emerging Strains of Avian Influenza Viruses

Location: Exotic & Emerging Avian Viral Diseases Research

Title: Pathobiology of Tennessee 2017 H7N9 low and high pathogenicity avian influenza viruses in commercial broiler breeders and specific pathogen free layer chickens

Author
item Bertran, Kateri - Consultant
item Lee, Dong-hun - Orise Fellow
item Criado, Miria - Consultant
item Smith, Diane
item Swayne, David
item Pantin-jackwood, Mary

Submitted to: Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2018
Publication Date: 8/29/2018
Citation: Bertran, K., Lee, D., Criado, M.F., Smith, D.M., Swayne, D.E., Pantin Jackwood, M.J. 2018. Pathobiology of Tennessee 2017 H7N9 low and high pathogenicity avian influenza viruses in commercial broiler breeders and specific pathogen free layer chickens. Veterinary Research. 49:82. https://doi.org/10.1186/s13567-018-0576-0.
DOI: https://doi.org/10.1186/s13567-018-0576-0

Interpretive Summary: An outbreak of highly pathogenic avian influenza (HPAI) H7N9 occurred in 2 broiler breeder farms in the state of Tennessee, USA in March 2017. Low pathogenicity avian influenza (LPAI) virus precursor was later detected in multiple broiler breeder farms and backyard poultry in Tennessee and neighboring states. In this study we examine the pathogenesis of the H7N9 LPAI and HPAI viruses in commercial broiler breeders and specific pathogen free (SPF) leghorn chickens. The mean bird infectious dose for the LPAI isolate was 4.3-5.6 log10 mean egg infectious doses, and virus shedding was almost exclusively from the oropharyngeal route. These findings suggest sub-optimal adaptation for sustained transmission with the H7N9 LPAI isolate, indicating that factors other than the birds’ genetic background may explain the epidemiology of the outbreak. The HPAI isolate had a lower bird mean infectious dose, was shed by both the oropharyngeal and cloacal routes, and transmitted to contacts. Greater susceptibility and easier transmission of the H7N9 HPAI virus could favor the spread of HPAI over LPAI viruses during outbreaks.

Technical Abstract: In March 2017, highly pathogenic avian influenza (HPAI) H7N9 was detected in 2 broiler breeder farms in the state of Tennessee, USA. Subsequent surveillance detected the low pathogenicity avian influenza (LPAI) virus precursor in multiple broiler breeder farms and backyard poultry in Tennessee and neighboring states. The pathogenesis of the H7N9 LPAI virus was investigated in commercial broiler breeders, the bird type mostly affected in this outbreak. Infectivity, transmissibility and pathogenesis of both the H7N9 HPAI and LPAI viruses were also studied in 4-week-old specific pathogen free (SPF) leghorn chickens. The mean bird infectious dose (BID50) for the LPAI isolate was 5.6 log10 mean egg infectious doses (EID50) for broiler breeders and 4.3 log10 EID50 for SPF layer chickens, and no transmission to contact-exposed birds was observed. In both bird types, virus shedding was almost exclusively from the oropharyngeal route. These findings suggest sub-optimal adaptation for sustained transmission with the H7N9 LPAI isolate, indicating that factors other than the birds’ genetic background may explain the epidemiology of the outbreak. The BID50 for the HPAI isolate in the SPF layer chickens was more than 2 logs lower (<2 log10 EID50) than the LPAI isolate. Also, the HPAI virus was shed by both the oropharyngeal and cloacal routes and transmitted to contacts. Greater susceptibility and easier transmission of the H7N9 HPAI virus are features of the HP phenotype that could favor the spread of HPAI over LPAI viruses during outbreaks.