Thread by @PeacockFlu

There have been some interesting developments with the panzootic (aka a pandemic of animals) H5N1 in mammals over the last few months.

Though I'd write a brief thread covering Polish cats, South American sealions and European fur farms.

Firstly, a quick situational update on the panzootic in birds. We're now 3 years into this outbreak and the virus is continuing to spread across the world, largely impacting waterfowl and seabirds (including many that are endangered)

https://twitter.com/guardianeco/status/1681980535843999744

Beyond birds though, we're seeing more and more infections in wild mammals that we've ever seen before. This is particularly widespread in scavengers and predators (for example foxes in Europe)

https://twitter.com/thijskuiken/status/1621143538821120003

In these cases it mostly looks as though these scavengers were directly infected by sick or dead birds and didnt appear to spread the virus on further. However recently there have been several clusters of mammalian infections that may represent mammal-to-mammal transmission

Firstly, the cats in Poland. This is a very unusual outbreak - over 30 cats with H5N1 infections throughout Poland, sequences are incredibly similar (no regional differences). All viruses share a pair of mammalian adaptations

https://twitter.com/CDCFlu/status/1682472787951099910

Something atypical has likely happened here. There has been suggestion of a shared food source (frozen raw meat?) which i think is very possible, however its harder to explain why every cat has the same mammalian adaptation...

https://twitter.com/k_pyrc/status/1682004814148911105

I think there are 2 potential explanations here.
1) there are viruses circulating in birds that somehow have these adaptations. This wouldnt be unprecidented and has happened in the past - sequences from wild birds in Poland partially supports this science.org/doi/10.1126/sc…

The second explanation is somehow meat or byproducts from infected mammals has somehow got into the pet foodchain (either directly, or as fodder for poultry).
Details of this investigation have been pretty sparse but I hope the source of this outbreak can be resolved quickly...

Secondly Sealions: Since H5N1 has entered South America there have been reports of mass mortality in both wild birds but also sealion colonies. Particularly on the Eastern coasts of Peru and Chile.

https://twitter.com/SERGIOLAMBERTUC/status/1624084780189995008

Genomic data has now been shared from both Chile and Peru. An unusual combination of mammalian adaptations suggests that there may be some stable transmission between sealions. In fact this same combination is also found in the Chilean human sequence...

https://twitter.com/DuckSwabber/status/1679293462313828352

This isnt the first potential case of sustained transmission of avian influenza in seals/sealions. I think theres fairly good evidence to suggest this 2011 North American outbreak might have done the same. This would be the first example with H5 though. journals.asm.org/doi/10.1128/mB…

Final point, fur farms - we need to have a serious conversation about whether it is a good idea to continue farming carnivores for fur during an H5N1 panzootic. @wendybarclay11 recently wrote an opinion piece for PNAS arguing its a really bad idea.

https://twitter.com/PNASNews/status/1682075204472782863

Several species of carnivore are farmed widely for fur in Europe and North America including mink, foxes and raccoon dogs. All of these are wild species (not domesticated) and are pretty universally kept in pretty miserable conditions.

There is a strong ethical arguement that fur farming is one of the most cruel farming practises out there. This lead to many countries outright banning the practise (including the UK).

However in our piece, we argue that there is a second reason fur farming is a bad idea. Mink (and foxes) are highly susceptible to H5N1. Normally wild foxes or mustelids (the family of animals that contains mink, polecats, ferrets, stoats etc) are fairly solitary.

Fur farming puts thousands of these animals together in close proximity, creating the perfect conditions for mammalian transmission and adaptation

For an H5 virus to become a human pandemic it would need to gain changes in the H5 haemagglutinin protein that enabled binding to human-like receptors, and allowed to to stay stable in airborne droplets (see below for a nice article on this topic)

https://twitter.com/kakape/status/1643993203799113730

We believe that very few mammals strongly select for these properties, but one that does is ferrets - ferrets are widely used as models for human influenza virus transmission, and for risk assessing emerging influenza viruses nature.com/articles/natur…

Mink are close relatives to ferrets. They are much less well studied than ferrets but the evidnece out there suggests they may similarly select for properties that could lead to efficient human to human transmission. tandfonline.com/doi/full/10.10…

Therefore, uncontrolled transmission of H5N1 through mink is a feasable pathway to the emergence of a human-transmissible, pandemic H5N1.

As the COVID-19 pandemic has demosntrated repeatedly, biosecurity on these farms is extremely weak - humans infect mink with SARS-CoV-2, mink re-infect humans. Mink also repeatedly get infected by H5N1, as well as human influenza strains

https://twitter.com/CIDRAP/status/1682464739924819969

the 3 last influenza pandemics arose from mixing between avian and human influenza viruses (sometimes within a swine host). Mink, being highly susceptible to both H5N1 and seasonal influenza could act as mixing vessels for these viruses tandfonline.com/doi/full/10.10…

As the outbreaks in mink farms in Spain, and most recently Finland show, H5N1 is not particularly deadly in these animals, therefore it is possible this can go under the radar (or be swept under the carpet). Unlike in birds, H5N1 in fur farms is not notifiable in many places...

To summerise - there have been some concerning developments with H5N1 recently - its still incredibly unclear how much of a pandemic threat this virus poses but there are real policy changes we can make to reduce that risk...

thanks for reading! Heres a list of good follows for more detailed info on these outbreaks:
For overall sitreps: @thijskuiken @DuckSwabber @FluTrackers @Fla_Medic
Polish cat outbreak: @k_pyrc sealions: @SERGIOLAMBERTUC Finnish fur: @aivelo @PikkaJokelainen @SmuraTeemu

(Also massive credit to all the academic and government labs doing surveillence and openly sharing sequences and reports, without them we would be completely in the dark!)

*West coasts (not East!)

narrator voice: it was not a brief thread

We're 1 week on and a couple of updates on some of these outbreaks. First off cats - frustratingly little update from the Polish cat outbreak - further sequences from wild birds/poultry shared but none have any mammalian adaptations. Still a big mystery what went on.

Cats in South Korea: Large outbreak in a cat shelter confirmed as H5N1 - investigation ongoing but very possible this could be cat-to-cat transmission (similar outbreaks have occured before in shelters with avian H7N2)

https://twitter.com/thijskuiken/status/1683865419143053312

Finnish fur farms: 19 farms total confirmed infected - mix of minks, raccoon dogs and foxes. I honestly suspect this is happening across many other countries that do fur farming but not being detected or reported...

https://twitter.com/PikkaJokelainen/status/1684258413390200856

Finland is giving out licences to cull wild birds in areas surrounding these farms. As many people are pointing out this is not a solution to this problem (and there is good reason to think it could make the situation worse)

https://twitter.com/aivelo/status/1684562797118783488

Culls of infected fur animals also appear to be underway soon at the farms but it sounds as though this is going to be pretty slow which is far from ideal

https://twitter.com/aivelo/status/1684519243860037632