Equine influenza, caused by the H3N8 subtype, is a highly contagious respiratory disease affecting equid populations worldwide and has led to serious epidemics and transboundary pandemics. This study describes the phylogenetic characterization and replication kinetics of recently-isolated H3N8 virus from a nasal swab obtained from a sporadic case of natural infection in an unvaccinated horse from Montana, USA. The nasal swab tested positive for equine influenza by Real-Time Quantitative Reverse Transcription Polymerase Chain Reaction (RT-PCR). Further, the whole genome sequencing of the virus confirmed that it was the H3N8 subtype and was designated as A/equine/Montana/9564-1/2015 (H3N8). A BLASTn search revealed that the polymerase basic protein 1 (PB1), polymerase acidic (PA), hemagglutinin (HA), nucleoprotein (NP), and matrix (M) segments of this H3N8 isolate shared the highest percentage identity to A/equine/Tennessee/29A/2014 (H3N8) and the polymerase basic protein 2 (PB2), neuraminidase (NA), and non-structural protein (NS) segments to A/equine/Malaysia/M201/2015 (H3N8). Phylogenetic characterization of individual gene segments, using currently available H3N8 viral genomes, of both equine and canine origin, further established that A/equine/Montana/9564-1/2015 belonged to the Florida Clade 1 viruses. Interestingly, replication kinetics of this H3N8 virus, using airway derived primary cells from multiple species, such as equine, swine, bovine, and human lung epithelial cells, demonstrated appreciable titers, when compared to Madin–Darby canine kidney epithelial cells. These findings indicate the broad host spectrum of this virus isolate and suggest the potential for cross-species transmissibility.
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This work was partially supported by SDSU AES 3AH-477, by National Science Foundation/EPSCoR (http://www.nsf.gov/od/iia/programs/epscor/index.jsp) award IIA-1335423, and by the state of South Dakota Governor’s Office of Economic Development as a South Dakota Research Innovation Center. Radhey S. Kaushik was funded and supported by USDA NIFA SDSU Agricultural Experiment Station Hatch grant # SD00H547-15. Thomas M. Chambers and Stephanie E. Reedy were supported by the Kentucky Agricultural Experiment Station (project no. KY014053).
Sreenivasan, Chithra C.; Jandhyala, Sunayana S.; Luo, Sisi; Hause, Ben M.; Thomas, Milton; Knudsen, David E. B.; Leslie-Steen, Pamela; Clement, Travis; Reedy, Stephanie E.; Chambers, Thomas; Christopher-Hennings, Jane; Nelson, Eric; Wang, Dan; Kaushik, Radhey S.; and Li, Feng, "Phylogenetic Analysis and Characterization of a Sporadic Isolate of Equine Influenza A H3N8 from an Unvaccinated Horse in 2015" (2018). Gluck Equine Research Center Faculty Publications. 22.