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Title: Deep sequencing of H7N8 avian influenza viruses from surveillance zone supports H7N8 high pathogenicity avian influenza was limited to a single outbreak farm in Indiana during 2016

Author
item LEE, DONG-HUN - Orise Fellow
item TORCHETTI, MIA - Animal And Plant Health Inspection Service (APHIS)
item KILLIAN, MARY - Animal And Plant Health Inspection Service (APHIS)
item Swayne, David

Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2017
Publication Date: 4/26/2017
Citation: Lee, D., Torchetti, M., Killian, M., Swayne, D.E. 2017. Deep sequencing of H7N8 avian influenza viruses from surveillance zone supports H7N8 high pathogenicity avian influenza was limited to a single outbreak farm in Indiana during 2016. Virology. 507:216-219. doi:10.1016/j.virol.2017.04.025.

Interpretive Summary: An outbreak of deadly H7N8 influenza (high pathogenicity) occurred in a single flock of turkeys in Indiana during January 2016. During surveillance testing in the Control Zone, eight cases of mild H7N8 influenza (low pathogenicity) were found in surrounding turkey flocks but no additional cases of deadly influenza. Genetic testing determined the mild and deadly forms of H7N8 influenza were closely related, and deadly form arose from the mild form on a single farm.

Technical Abstract: In mid-January 2016, an outbreak of H7N8 high pathogenicity avian influenza (HPAI) virus in commercial turkeys occurred in Indiana. The outbreak was first detected by an increase in mortality followed by laboratory confirmation of H7N8 HPAI virus. Surveillance within the 10 km Control Zone detected eight H7N8 low pathogenicity avian influenza (LPAI) viruses in surrounding turkey flocks but no other HPAI affected premises. Additionally, two dangerous contact premises, an additional turkey flock and a chicken layer flock, were identified, but without detection of either the H7N8 HPAI or LPAI viruses. Sequencing and phylogenetic network analysis of the H7N8 HPAI virus isolated from index farm and seven LPAI viruses indicated all the viruses were closely linked genetically and the progenitor H7N8 LPAI viruses circulated between turkey farms in Indiana, followed by spontaneous mutation to a HPAI virus on a single premise by insertion of 9 nucleotides at the hemagglutinin cleavage site. Deep sequencing of the LPAI isolates failed to identify any subpopulations of HPAI virus suggesting the HPAI virus did not spread to epidemiologically-linked LPAI affected farms.