One Health Adv.: Mink Infection With Influenza A Viruses - An Ignored Intermediate Host?

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Fourteen years ago, in 2009's That Touch Of Mink Flu, we took the first in a series of looks at the potential for farmed (or wild) mink to serve as a `mixing vessel' for influenza A viruses.  

That first blog was inspired by an announcement by Danish authorities that at least 11 mink farms in their Holstebro region were infected with a variant of the human H3N2 virus.  

We also reviewed some of the history of mink infection with influenza, going as back as far as an H10N4 outbreak in Sweden in 1984, and reports of an H5N1 mink infection (again in Sweden) in 2006.

We would revisit the topic a number times over the next decade, including 2015's That Touch Of Mink Flu (H9N2 Edition), where we looked at a serological survey of antibodies to H9N2 (along with H5 & H7 viruses) in Chinese farmed minks, along with the results of experimental infection of minks with the H9N2 virus.

For a review of other relevant mink studies, you may wish to revisit last January's  That Touch of Mink Flu (2023 Edition).

Following several high-profile outbreaks of COVID in farmed mink, last fall we saw a large outbreak of avian H5N1 at a mink farm in Spain (see Eurosurveillance journal report HPAI A(H5N1) Virus Infection in Farmed Minks, Spain, October 2022).

Not only does it appear likely that the H5N1 virus spread efficiently from mink-to-mink, it picked up a rare, and potentially dangerous, mutation (T271A) along the way, one which reportedly `enhances the polymerase activity of influenza A viruses in mammalian host cells and mice'.

In late February we saw an an analysis from Denmark's SSI which found a Low to Moderate Risk of Human Infection With Bird Flu From Mink. From their risk assessment:

Development of virus variants in mink that have an increased risk of infection to and between humans (adapted viruses)

There is a theoretical risk that by passage in mink over a longer period of time variants may be developed that are better adapted to mammals and therefore perhaps also to humans. Studies of avian influenza A virus infection in other animals, including wild mammals and ferrets, have shown that adaptive mutations occur quickly both at first exposure and when the virus passes from animal to animal (20).

In a situation where mink have already been infected with HPAI and the virus spreads between mink, it is considered to be very likely (cf. EFSA criteria) that variants of HPAI can develop that are adapted to mammals and thereby also potentially adapted to people. The certainty of this assessment is low. The consequence in the worst case will be that a variant of the virus arises that can be transmitted from person to person, and thus trigger widespread social contagion.

Early recognition of the HPAI virus in mink and humans is therefore essential to reduce the overall health risk. 

 

All of which brings us to a new review in the Journal One Health Advances, that looks at the susceptibility of mink to influenza A viruses, and the potential for mink to act as `mixing vessels' for influenza.  

While this review covers some familiar ground, it also provides a good deal of information about influenza infection of farmed mink in China by a variety of avian and human viruses, including the detection of some worrisome mammalian adaptations. 

Mink farming has become big business in China over the past 20 years, with 2/3rds of the world's mink farms located there. Reportedly fox and raccoon dogs are raised on many of these same farms, increasing the odds of inter-species transmission of novel viruses.

I've only reproduced the Abstract below, so you'll want to follow the link to read it in its entirety.  I'll have a brief postscript when you return. 

Mink infection with influenza A viruses: an ignored intermediate host?

Chris Ka Pun Mok & Kun Qin

One Health Advances volume 1, Article number: 5 (2023) Cite this article

Abstract

Continuously emergence of human infection with avian influenza A virus poses persistent threat to public health, as illustrated in zoonotic H5N1/6 and H7N9 infections. The recent surge of infection to farmed mink by multiple subtypes of avian influenza A viruses in China highlights the role of mink in the ecology of influenza in this region.

Serologic studies suggested that farmed mink in China are frequently infected with prevailing human (H3N2 and H1N1/pdm) and avian (H7N9, H5N6, and H9N2) influenza A viruses.

Moreover, genetic analysis from the sequences of influenza viruses from mink showed that several strains acquired mammalian adaptive mutations compared to their avian counterparts. The transmission of SARS-CoV-2 from mink to human alerts us that mink may serve as an intermediate host or reservoir of some emerging pathogens.

Considering the high susceptibility to different influenza A viruses, it is possible that mink in endemic regions may play a role as an “mixing vessel” for generating novel pandemic strain. Thus, enhanced surveillance of influenza viruses in mink should be urgently implemented for early warning of potential pandemic.

          (SNIP)

     (Continue . . . )                   

The superpower possessed by influenza A viruses is their ability to abruptly reinvent themselves via reassortment (aka `Antigenic Shift'), which is the most likely way that a pandemic flu virus will emerge (see 3 min. NIAID Video: How Influenza Pandemics Occur).

While pigs - which are raised in far greater quantities - are viewed as being the biggest `mixing vessel' threat, mink farms appear to offer an excellent breeding ground for novel viruses as well. 

Granted, even without mink farms, another pandemic is inevitable. 

But the practice of raising millions of highly (flu & COVID) susceptible mammals in the confined environment of fur farms only adds to the pandemic threat, and could potentially speed up the arrival of the next global health crisis.