#18,522
We've known of the susceptibility of mink to influenza infection for quite some time. Fifteen years ago, in 2009's That Touch Of Mink Flu, we looked at a story out of Denmark, where at least 11 mink farms in the Holstebro were reported to be infected with a variant of the human H3N2 virus.
- Also in 2009, an H3N2 Swine Influenza was detected in Canadian Mink, reported in a Journal of Clinical Microbiology study called Characterization of a Canadian Mink H3N2 Influenza A Virus Isolate Genetically Related to Triple Reassortant Swine Influenza Virus.
- Three years earlier (2006) CIDRAP reported on a European mink found infected with an aggressive form of the H5 flu virus in the Blekinge region of southern Sweden near where H5N1 had been detected in wild birds.
- And more than 40 years, a large outbreak in Swedish mink farms was found to be due to the H10N4 avian virus.
In 2015, we revisited mink flu (see That Touch Of Mink Flu (H9N2 Edition), after a study published in the Virology Journal found antibodies to H9N2 (along with H5 & H7 viruses) in Chinese farmed minks.
In 2019, in Nature: Semiaquatic Mammals As Intermediate Hosts For Avian Influenza a research article published in Nature examined the fitness of a number of small semiaquatic mammals (including mink) to serve as intermediate hosts - and potential mixing vessels - for novel flu.
In 2020, we also learned that mink were highly susceptible to COVID after new strains emerged from infected farm-raised mink in several countries, some of which went on to infect humans in the community (see Denmark Orders Culling Of All Mink Following Discovery Of Mutated Coronavirus).
Concerns were amplified once again in the fall of 2022, when a mutated H5N1 virus was found in farmed mink in Spain (see Eurosurveillance: HPAI A(H5N1) Virus Infection in Farmed Minks, Spain, October 2022).
Over the summer and fall of 2023 more than 70 Finnish fur farms - raising a mixture of mink and foxes - were found to be infected with H5N1, forcing the culling of a half million animals.
Last summer, in PNAS: Mink Farming Poses Risks for Future Viral Pandemics, we looked at an opinion piece by Professor Wendy Barclay & Tom Peacock on why fur farms - and mink farms in particular - are high risk venues for flu.
Despite these repeated warning signs, surveillance and testing of farmed animals for novel flu viruses remains quite limited. Many farmers - fearing economic losses - are unwilling to report suspect cases, or to allow routine testing.
Today we've another cautionary report out of Canada, where a reassortant H3N2 virus was detected in farmed mink in 2021. This reassortant has subsequently turned up in swine in the American Midwest, and in swine and turkeys in Ontario.
This is a fascinating report, very much worth reading in its entirety. I've only posted some excerpts below. I'll have a bit more after the break.
Kevin S. Kuchinski, John Tyson, Tracy Lee, Susan Detmer, Yohannes Berhane, Theresa Burns, Natalie A. Prystajecky, Chelsea G. Himsworth
First published: 29 December 2024 https://doi.org/10.1111/zph.13205
Funding: This work was funded by the Genome British Columbia as part of the One Health Genomics: COVID-19 Adaptation investigation in mink (Mink ALERT, Cov-200).
ABSTRACT
Introduction
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.
Methods
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.
Results
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.
Conclusions
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.
Summary
- IAV infections in mink are likely under detected.
- Circulation of IAVs in mink raises public health concerns over zoonotic influenzas.
- IAV surveillance in mink can be useful for zoonotic risk awareness due to their exposure to other livestock and their physiological similarities to humans.
(SNIP)
While this study was unable to identify the local source of this outbreak, it did provide valuable insights. Foremost, it highlighted the need for more extensive genomic surveillance of IAVs in classic livestock hosts like swine and poultry. It also highlighted the need to expand surveillance to other types of livestock that are not considered classic IAV hosts, like mink.
Recent reports of highly pathogenic H5N1 avian influenza infections in American dairy cattle further demonstrate that IAVs may be more widespread in our livestock populations and food systems than previously imagined (Burrough et al. 2024; Caserta et al. 2024).
Increased surveillance would assist outbreak investigations and further reveal the type of exposures that are responsible for IAV infections in mink and other livestock. Drawing these connections may also advance our understanding of environmental transmission between farms, which would improve infection prevention and control practices for all livestock industries impacted by IAV spillovers. Finally, heightened genomic surveillance of IAVs in swine and mink would increase detections of well-adapted reassortments, improving pandemic preparedness.
The authors wisely call for enhanced surveillance and testing, but `Don't test, don't tell' remains the preferred strategy for many farmers. Regulatory agencies, meanwhile, have been slow to or reluctant to react.
Which is why 9 months after it was first detected, we still don't have a good handle on how widespread HPAI H5 is in cattle, and other livestock (including in pigs, and other farmed animals).
Nor do we know how many human infections have really occurred, since testing has been voluntary, sporadic, and largely limited to obviously symptomatic farmworkers.
We may get away with wearing blinders for a time - and H5N1 may yet fizzle - but allowing a growing array of zoonotic viruses to spread unfettered and unmonitored in livestock is a risky strategy.
One that will be hard to justify if the worst happens.
