#18,086
Fifteen years ago, during the height of the 2009 H1N1 pandemic - in That Touch Of Mink Flu - we started looking at the close relationship between influenza and mink farms. At that time, Denmark was reporting the discovery of a novel H3N2 virus circulating on at least 11 mink farms in Holstebro.
While this wasn't the first detection of Influenza A in farmed mink, it set off alarm bells because it involved a `humanized' strain, and it had spread rapidly through multiple farms.
Earlier that same year, a report was published in the Journal of Clinical Microbiology, describing a 2007 outbreak of swine H3N2 among farmed mink in Canada. Prior to that - in 2006, a mink was discovered to have highly pathogenic H5N1 `bird flu’ in Sweden (see CIDRAP Report).
Since then, we've revisited the mink-flu connection many times, and starting in 2020, its equally close relationship with COVID. A few of many blogs include:
Nature: Semiaquatic Mammals As Intermediate Hosts For Avian Influenza
Although our biggest mink-related concerns currently involve H5N1 and COVID, we've a preprint today on the finding of an H3N2 reassortant virus circulating on a remote mink farm in British Columbia. This discovery was only made because they were monitoring for COVID, which suggests flu outbreaks in mink are likely far more common than we know.
While its origins remain murky, this `swine-human reassortment' has since been detected in both birds and swine across central Canada and the United States.
Today's report not only characterizes the virus, it spends a good deal of time trying to determine how this reassortant reached, and established a home, on this remote mink ranch.
I've reproduced the abstract and some excerpts from the preprint, but I highly recommend reading the full 29-page report. I'll return with a brief postscript after the break.
Detection of a reassortant swine- and human-origin H3N2 influenza A virus in farmed mink in British Columbia, Canada
Kevin S Kuchinski, John Tyson, Tracy Lee, Susan Detmer, Yohannes Berhane, Theresa Burns, Natalie A Prystajecky, Chelsea Himsworth
doi: https://doi.org/10.1101/2024.05.27.596080
Preview PDF
Abstract
In December 2021, influenza A viruses (IAV) were detected in a population of farmed mink in British Columbia, Canada. Based on genomic sequencing and phylogenetic analysis, these IAVs were subtyped as H3N2s that originated from reassortment of swine H3N2 (clade 1990.4h), 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.
(SNIP)
On 2 May 2021, an outbreak of SARS-CoV-2 was detected on an American mink farm (Neovison vison) in BC through a passive surveillance program. This program had been instituted by the Ministry of Agriculture and Food (MAF) in response to two previous SARSCoV-2 outbreaks on mink farms in BC. The outbreak continued until April 2022, at which point the farm was depopulated.
ResultsNo unusual clinical signs were reported in the herd, nor was there increased incidence of respiratory disease or mortality. During the surveillance period, SARSCoV-2 prevalence and evolution was monitored by testing a random stratified sample of 65 mink every two weeks.Testing was conducted by the BC Centre for Disease Control Public Health Laboratory (PHL), where SARS-CoV-2 assays had been multiplexed with IAV, influenza B virus, and respiratory syncytial virus for higher laboratory throughput during the COVID-19 pandemic. This led to the incidental detection of IAV in 17 of 65 mink specimens on 3 Dec 2021.
DiscussionOur investigation could not conclude how these mink became exposed to swine-origin IAVs. Additional modes of transmission were considered, but they could not be assessed due to lack of available data. For instance, wild mustelids have been reported to visit mink farms and interact with captive animals resulting in the transmission of viruses30; it is possible that wild mustelids may have visited this farm unnoticed after becoming infected with IAVs on another premise where swine are raised.(SNIP)Ultimately, the limited extent of genomic surveillance for IAVs in local swine and poultry populations constrained our ability to identify a local source for the outbreak. It also restricted our ability to assess the plausibility of different transmission routes.
Although IAV is a reportable disease in swine and poultry in BC, the passive nature of surveillance programs combined with the potential for asymptomatic or unremarkable infections means that underreporting and under-detection is likely.Indeed, only 4 contemporaneous, local swine-origin H3N2 IAV genomes were available for analysis, opportunistically detected through an unrelated research study, and these viruses were not related to the mink farm outbreak. This suggests that IAV diversity within swine populations is under-characterized.This was further indicated by limited detections of IAVs with the same genome constellation as far afield as Iowa, Minnesota, Missouri, and Ontario. This suggests that this IAV reassortant was able to disseminate across North America largely unnoticed.
While people tend to think of farming as natural and safe, modern farming practices are a far cry from the family farms of yesteryear. Pigs, in particular, are often transported cross-country, to be fattened - and then slaughtered - in the most economical way.The uncomfortable corollary is that many other reassortant IAVs are likely emerging and disseminating unobserved within large, transnational, commercial swine populations.
Crowded factory farms can serve as `breeder reactors', co-mingling and amplifying viruses that come from multiple locations around the country. In that way, they are not unlike unintentional, and unmonitored, GOF (Gain of Function) experiments.
Despite the growing dangers, testing, surveillance, and reporting are often either passive, voluntary, or in some places; practically non-existent.
Even here in the United States, where H5N1 is unexpectedly spreading widely in diary cattle, testing (except for interstate transport) remains extremely limited and voluntary. As a result, we don't really know how widespread the problem really is.
While it is somewhat reassuring that H5N1 has yet to turn up in American pigs - which is potentially far more risky than in cattle - limited testing can only provide limited confidence.
I have to believe 10 or 20 years from now - when historians look back at our next major pandemic - they will be completely mystified by our willingness to accept a `Don't test, don't tell' policy in the face of a clear and present danger like H5N1.
I know I'm dumbfounded now.
