Detection of a Reassortant Swine- and Human-Origin H3N2 Influenza A Virus in Farmed Mink in British Columbia, Canada

In December 2021, influenza A viruses (IAV) were detected in a population of farmed mink in British Columbia, Canada. Circulation of IAVs in farmed mink populations has raised public health concerns due to similarities between mustelid and human respiratory physiology, potentially facilitating spillover of zoonotic influenzas from livestock.

Oropharyngeal specimens were collected from mink as part of a surveillance program for SARS-CoV-2. Diagnostic RT-qPCR testing was performed using a multiplex assay targeting SARS-CoV-2, IAV, influenza B virus and respiratory syncytial virus. Whole viral genome sequencing was conducted on IAV-positive specimens, followed by phylogenetic analysis with other animal and human IAV genome sequences from large global databases.

IAVs were detected in 17 of 65 mink by RT-qPCR. Based on genomic sequencing and phylogenetic analysis, these IAVs were subtyped as H3N2s that originated from reassortment of swine H3N2 (clade 1990.4 h), human seasonal H1N1 (pdm09) and swine H1N2 (clade 1A.1.1.3). This reassortant has been subsequently observed in swine in several Midwest American states, as well as in swine and turkeys in Ontario, suggesting its spillover into farmed mink in British Columbia was incidental to its broader dissemination in North American swine populations.

These detections reaffirm the need for extensive genomic surveillance of IAVs in swine populations to monitor reassortments that might become public health concerns. They also highlight the need for closer surveillance of IAVs in mink to preserve animal health, protect agricultural interests, and monitor potential zoonotic threats.