Fur Farms
The airways of Minks are similar to those of humans and they are highly susceptible to influenza viruses. H5N1 infections of minks are very lethal, unlike the asymptomatic H5N1 infections of pigs. As predatory carnivores, they are fed animal byproducts unfit for human consumption. This may include cheese and fish, but also raw poultry and meat. Any bird reckless enough to get close to the cages, maybe to steal food, can quickly become part of the mink diet.
European minks are closely related to ferrets, which essentially are domesticated polecats. Less related to both are American minks, which were imported to Europe for fur farming. They are an invasive species and seem to reduce the female polecat population.
Various fox species are kept on fur farms, sometimes on the same farms as the minks.
Already during the Covid-19 pandemic minks made headlines because the minks infected people with a dangerous variant and the entire mink population of Denmark was culled. Mink farming was prohibited in Denmark until 2023. It became legal again on the first of January 2023. At this time there were already reports about an H5N1 outbreak on a Spanish fur farm. Now there are H5N1 outbreaks on more than 20 fur farms in Finland. PCR tests for H5N1 or antibody tests for H5N1 antibodies have been positive on more than 70 fur farms.
Experimental and field evidence have demonstrated that minks are susceptible and permissive to both avian and human influenza A viruses, leading to the theory that this species could serve as a potential mixing vessel for the interspecies transmission among birds, mammals and human. In light of this and considering the ongoing HPAI H5N1 panzootic, our findings further highlight the importance of preventing mink infection with such viruses.
Swine are often cited as the vessel because pigs are susceptible to many avian and human strains. Pigs, however, are somewhat refractory to H5N1 infections, including the currently panzootic clade 2.3.4.4b viruses. Mink clearly are not. Mink farms could provide ample opportunity for the reassortment between H5 subtype avian influenza viruses and human-adapted strains.
Under many current regulatory authorities, an equivalent laboratory “experiment” of this nature would be classed as “gain of function” research and therefore prohibited. Even if it were approved, regulations would require that it be performed under high-containment conditions following an extensive risk–benefit assessment. Current practice in mink farms opens up the possibility for similar adaptation to occur in a completely unregulated and uncontrolled manner.
As recently as October 2022, there were disturbing reports of sustained transmission of the panzootic, highly pathogenic avian influenza (H5N1) at a Spanish mink farm. At least one mammalian adaptation in the virus polymerase emerged in the mink during this outbreak; in all likelihood, we narrowly escaped a larger disaster, as the incident appears to have been contained.
Ferrets Mustela putorius fero are the only truly domesticated mustelid and are descended from European polecats. Not much is known about the history of their domestication but it is thought to have occurred around 2500 years ago for the purpose of hunting rabbits and rodents.
(...) American mink are a recent arrival, brought to the UK in the 1920’s to
be farmed for their fur, they are now widespread and have had a severe
negative impact on native wildlife, in particular water voles but they
could also impact European polecat populations.
Ferrets are domesticated European polecats (Mustela putorius), and only ferrets are kept as pets. Minks are too wild to be pets, although they are used for ratting, and European minks (Mustela lutreola) are more related to polecats than to North American minks (Neogale vision).
When you make cheese, when you age cheese, there’s mold on the outside and so they trim them all off and then in order to square it up to get your nice slices for the store, you get all the odd-shaped trimmings.
That’s the type of thing that goes into mink food. And then also the by-products from the pork and poultry and beef industry.
Several types of animals are commercially farmed for fur production in Finland, including American mink (Neovison vison), arctic (blue) fox (Vulpes lagopus), red (silver) fox (V. vulpes) and their crossbreeds, raccoon dog (Nyctereutes procyonoides) and sable (Martes zibellina). There are over 500 farms in the country, and 95% of the fur production (1.3 million animals annually) is concentrated in western Finland.
The monogamous, hibernating canids, which are related to foxes, are sold for meat and fur.
Officials initially thought mink at the farms contracted the virus from humans, but based on genome analysis they now think a farm worker got sick from the mink. This week, the government also reported that feral cats may be spreading the virus between fur farms, noting that the pathogen identified at two infected farms looked closely related and that three out of 11 cats that roam the grounds of one farm had antibodies to the coronavirus.
One strain of mutated SARS-CoV-2, found in 12 humans in Denmark, appeared in laboratory tests to exhibit “decreased susceptibility” to antibodies from previously infected people, the country’s State Serum Institute said in a preliminary report.1 This variant, if it spread, might be less easily controlled by covid-19 vaccines currently under development, the report warned.
The only safe option, said Danish prime minister Mette Frederiksen, is to cull all 17 million minks kept by the Danish fur industry. Denmark is the world’s biggest mink fur exporter, supplying about a third of global demand.
After a two-year ban, Denmark will once again allow mink farming from January 2023.
Denmark was one of the world’s main mink fur exporters, producing an estimated 17 million furs per year. Kopenhagen Fur, a cooperative of 1,500 Danish breeders, accounts for 40% of global mink production. Most of its exports went to China and Hong Kong.
There are over 500 farms in the country, and 95% of the fur production (1.3 million animals annually) is concentrated in western Finland.
“We have two generations of really skilled mink farmers, father and son, who in a very, very short time have had their life’s work shattered,” Frederiksen told reporters after a meeting with a mink farmer and his son at their farm near Kolding in Western Denmark. “It has been emotional for them, and... Sorry. It has for me too,” Frederiksen said with a wavering voice, pausing for breath in between words.
Mammal-to-Mammal Transmission?
It seems to be obvious that mammal-to-mammal transmission has occurred on the fur farms. But it is worth to keep in mind that the cause of infection of more than 10.000 sea lions and seals is still disputed and individual bird-to-mammal fecal-to-oral route infections due to widespread fecal contamination may still account for the majority of the infections or even all of them, although unlikely.
With the infections progressing from cage to cage, there is hardly any other explanation than mammal-to-mammal transmission. Nonetheless a recent study concluded that two virus samples from the mink farm in Spain were not transmissible through respiratory droplets.
In theory, all of the sick animals could have picked up the virus from their feed, which included poultry byproducts, but H5N1 outbreaks have not been reported in the region where the poultry farms and slaughterhouses supplying the feed are located. And the virus spread from pen to pen as expected if it was transmitted between mink.
Our findings also indicate that an onward transmission of the virus to other minks may have taken place in the affected farm. This is suggested by the increasing number of infected animals identified after the confirmation of the disease and the progression of the infection from the initially affected area to the entire holding.
Phylogenetic analyses further suggest that several introductions from birds to the fur animals may have taken place but are also consistent with possible transmission among the fur animals themselves and potentially even between species. Transmission between fur animals is also supported by the general epidemiological pattern of several hundreds of sick and dead animals on the 20 farms (mortality on affected farms has been 2–4 times the normal rate and, at the peak of the outbreak, a large farm recorded almost 400 deaths in one day, which is 10 times the normal rate). The exact mechanism of the transmission within and between farms is, however, not yet known.
Ferrets aren't humans, but in studies to date, any influenza strain that has been able to pass among ferrets has also been transmissible among humans, and vice versa, says Fouchier: "That could be different this time, but I wouldn't bet any money on it."
Collectively, our data demonstrate that two different clade 2.3.4.4b mink viruses are highly virulent in mice and ferrets but do not transmit to exposed ferrets through respiratory droplets.
Outbreaks of highly pathogenic H5N1 clade 2.3.4.4b viruses in farmed mink and seals combined with isolated human infections suggest these viruses pose a pandemic threat. To assess this threat, using the ferret model, we show an H5N1 isolate derived from mink transmits by direct contact to 75% of exposed ferrets and, in airborne transmission studies, the virus transmits to 37.5% of contacts. (...) Collectively, experimental data indicate that some clade 2.3.4.4b viruses of both the North American and Eurasian lineages transmit between ferrets that are in direct contact and that these viruses possess potential for limited airborne transmission. These findings emphasize the pandemic potential of clade 2.3.4.4b H5N1 viruses. (...) In conclusion, this is the first report of both direct contact and limited airborne transmission in a mammalian model of a subclade 2.3.4.4b H5N1 virus indicating these viruses pose a significant pandemic threat.
Spain, Galicia: The First Fur Farm Outbreak
The first H5N1 outbreak on a fur farm happened in October 2022 in Spain. This large farm housed 52.000 minks. A very high lethality was observed and the infections spread from cage to cage, strongly suggesting mammal-to-mammal transmission.
The mortality pattern at that time was characterised by multiple ‘hot spots’ within the affected barns consisting of 2–4 pens where all the animals died within a period of 1–2 days. In the following weeks, the mortality increased also in the neighbouring barns and the whole premises was affected. Clinical signs of infection in minks included loss of appetite, hypersalivation, depression, bloody snout and neurological manifestations such as ataxia and tremors.
The mink viruses showed between 8 and 9 amino acid differences in the PB2, PB1, PA, NA, NS2, M2 and PB1-F2 with the most closely related H5N1 viruses. In particular, all of the viruses from minks present an alanine (A) at position 271 of PB2 (T271A), which enhances the polymerase activity of influenza A viruses in mammalian host cells and mice. At the time of writing, of the HPAI H5 viruses sequenced in Europe since autumn 2020, this mutation was identified only in a H5N1 virus collected from an infected European polecat in the Netherlands in March 2022. Based on the publicly available sequences, the other mutations have never (PB1–388R, NA-74S, NS2–13G) or rarely (PB1–317V, PA-56T, NA-163L, PB1-F2–30L) been identified in HPAI H5Nx viruses detected in Europe since 2021 and their biological impact is unknown.
Of note, from April 2020 onwards, following the first identification of SARS-CoV-2 infection in mink farms in the Netherlands, the use of a face mask was made compulsory for all farm workers on mink farms in Spain. Since the SARS-CoV-2/HPAI suspicion was raised on 4 October 2022, increased biosafety measures including the use of disposable overalls, face shields, face mask changing (twice per day) and frequent handwashing were applied in the farm. Workwear was washed at the farm and showering before leaving the farm was also encouraged. All unnecessary activities at the premises were discontinued.
On 13 October, the animal health services conducted a census to estimate the number of minks at the investigated farm, which amounted to 51,986 animals.
Dr Tom Peacock, a virologist and fellow at the Pirbright Institute agreed: “This latest case wouldn’t be the first time there have been concerns H5N1 could be moving through different mammals via contaminated feed,” citing the outbreak of avian flu in cats in Poland last year, which experts suspected might have been transmitted through mink byproducts used in raw cat food.
Finland: 70+ Fur Farms Outbreaks
In the summer of 2023 outbreaks of H5N1 were detected in several fur farms in Finland. This study covers outbreaks on 20 different fur farms with 148.000 foxes or racoon dogs and 38.000 minks in Finland based direct evidence of the presence of the virus due to PCR testing. But at least 50 more farms have been declared affected. Just like in Spain the virus seems to be transmitted from one cage to the next. The genetic data implicates that the outbreaks have been caused by birds. The emergence of H5N1 at roughly the same time in over 20 farms indicates that with the H5N1 variant circulating in birds at this time, the risk of additional outbreaks on fur farms is extremely high. The testing of all fur farms in Finland for antibodies raises questions about the validity of seroevidence, similar to the debate about possible human infections and the CFR. As of June 2024, 72 farms have been depopulated.
Some evidence for adaptation to replication in mammals is evident, as the PB2 gene E627K change was detected in samples from one farm and the T271A change in a sample from another farm.
To date, 27 July 2023, 20 affected farms in four municipalities of Central and South Ostrobothnia have been identified with blue and silver foxes and their crossbreeds, raccoon dogs and minks being infected. The affected farms, which vary in size from 600–50,000 fur animals, house a total of 37,900 minks, 142,463 foxes and 5,400 raccoon dogs (a total of 185,763 fur animals, each farm rearing 1–3 species).
Phylogenetic analyses further suggest that several introductions from birds to the fur animals may have taken place but are also consistent with possible transmission among the fur animals themselves and potentially even between species. Transmission between fur animals is also supported by the general epidemiological pattern of several hundreds of sick and dead animals on the 20 farms (mortality on affected farms has been 2–4 times the normal rate and, at the peak of the outbreak, a large farm recorded almost 400 deaths in one day, which is 10 times the normal rate). The exact mechanism of the transmission within and between farms is, however, not yet known.
The sequence data indicate that, at least originally, transmission likely occurred from birds to the fur animals, most probably through contacts in the shade houses. Birds have easy access to the interior of the shade houses and gulls have frequently been observed in the vicinity of the farms. Mass deaths of gulls have also occurred in the same general region.
At the end of September, the Finnish Food Authority has switched to antibody testing only in the avian influenza survey of fur farms. As a result of the Authority's new policy, tens of thousands of healthy fur animals are ordered to be killed, contrary to the purpose of the Animal Diseases Act about proportionate measures and contrary to sufficient medical evidence.
In summary, antibody tests only show whether the animal has antibodies against influenza or avian influenza in the blood. This means that the animal has apparently at some point encountered the influenza virus and developed antibodies (resistance) to it, but the animals are not in any way sick or symptomatic. There is no international data on the duration of antibody detection in animals' blood counts and the current diagnosis is inadequate. Antibodies may even be passed on from mothers to pups, so that an animal with antibodies may not ever have encountered the avian influenza virus while living.
The country's Ministry of Agriculture and Forestry issued a decree on Monday that requires fur farms to take measures to avoid contact between fur animals and birds, as well as other harmful animals and their excrement.
Under the decree, the openings of shelters, halls and other animal holding facilities in fur farms must be closed with a net to stop birds from the facilities. The mesh size of these nets may not exceed 25 x 25 millimeters.
The legislation also stipulates measures to repel other harmful animals, and to ensure the safe distribution of feed and the protection of feedstocks.
As a result, the Finnish Food Authority ordered all the animals at 72 fur farms, totalling around 500,000, to be culled. The order to cull is based on protecting human health.
New monitoring of avian influenza at fur farms will start in the first week of June. The monitoring will continue until the end of September. This is the period when the risk of infection from wild birds is at its highest. Protection obligations for fur farms have also been strengthened, enforcement is being monitored and different authorities have issued guidance on protection against avian influenza.
As part of the monitoring, each fur farm must submit to the Finnish Food Authority three animals that have either died or been put down due to poor condition, for examination every three weeks. The Finnish Food Authority will organise the transport of dead animals for laboratory tests. If a farm fails to provide samples for monitoring, a municipal veterinarian will visit the farm to take samples. In addition, if avian influenza is suspected at a farm, for example because of symptoms or increased mortality, a municipal veterinarian will also visit the farm to take samples.
The fur farmer is obliged to inform the municipal veterinarian of any suspicious symptoms and mortality of animals. Fur farmers must also protect their animals from avian influenza infections spread by wild animals. Decree 14/2024 of the Ministry of Agriculture and Forestry requires, among other things, the protection of facilities housing livestock with bird nets between mid-April and the end of October. Municipal veterinarians are monitoring compliance with the requirements of the decree at fur farms.
Finland plans to offer preemptive bird flu vaccination as soon as next week to some workers with exposure to animals, health authorities said on Tuesday, making it the first country in the world to do so.
The Nordic country has bought vaccines for 10,000 people, each consisting of two injections, as part of a joint EU procurement of up to 40 million doses for 15 nations from manufacturer CSL Seqirus.
The Australian company in a statement to Reuters said Finland would be the first country to roll out the vaccine.
"The vaccine will be offered to those aged 18 or over who are at increased risk of contracting avian influenza due to their work or other circumstances," the Finnish Institute for Health and Welfare (THL) said in a statement.
The vaccine has been developed by the Australian-owned company CSL Seqirus (CSLS) at its main UK manufacturing plant in Speke, Liverpool.
They have already been used to protect workers in Finland, where H5N1 spread amongst farmed mink last year. The Finnish government procured 10,000 doses – although only 450 people took up the offer to get jabbed.
