Pneumonia, bloody muzzle, tremors, sudden rise in mortality. Funny symptoms affected the minks of an intensive fur production operation, in early October 2022, in the Spanish province of Galicia. The main suspect, Covid-19, has been ruled out. It is a much more dangerous virus that has been detected: a subtype of avian influenza, in its most formidable form for humans, the H5N1.
The event is enough to panic the health authorities. So far the virus H5N1 highly pathogenic avian influenza has infected humans very rarely since it was first identified in commercially farmed geese in 1996 in southern China. On the other hand, when it did – for example in Hong Kong in 1997, again through direct and prolonged contact with poultry – nearly half of the people died. More precisely, l’OMS lists 868 cases since 2003 including 53 % fatal. If this virus acquires the capacity to be transmitted durably, from person to person in the human population, it could trigger a new pandemic, with a human toll much higher than that which we have known for Covid-19.
The international scientific community agrees that a worrying step has been taken in this direction, following the contamination of mink farming in Galicia. First spotted in a building, the infection gradually spread to the entire farm, where nearly 52,000 animals lived in cages. A rare mutation of the virus H5N1 likely to facilitate human-to-human transmission has been identified. On October 18, 2022, the slaughter of animals began. Tested negatively, the employees had fortunately not yet caught it. They were isolated for ten days as a precaution. A chance for this time: the health surveillance system worked.
- Presence of avian flu in the Paracas National Reserve, Peru, on January 23, 2023. A) Sea lion carcasses on the beach ; B) Dead sea lion with ataxia ; C) Dead sea lion showing symptoms of bird flu ; D) Sampling for RT–PCR ; E) Sea lion necropsy ; F) Sea lion eating an infected animal. Photos from a study published on February 10, 2023
The more it contaminates, the greater the risk for humans
Nevertheless, the event did indeed alarm the scientific community. While it is quite exceptional, the flu H5N1 transmitted between mammals. And above all, for the first time in Europe, this virus spread from mink to mink probably by airborne transmission, as the flu does between humans. « This is suggested by the increasing number of infected animals identified after confirmation of the disease and the progression of infection from the initially affected area to the whole farm. »explain the authors ofan article on this breeding published in Eurosurveillancea journal of epidemiology.
However, when they are infected with avian influenza, minks do not normally transmit it by this route, because they store these viruses in the lower respiratory tract. On the other hand, when they are affected by human flu, they actually communicate it to each other by air, for example by sneezing, a very effective way of spreading a virus.
This is all the more alarming, as from mink to humans, the species barrier is tenuous. Like the ferret, its lung physiology makes it an excellent laboratory animal model for understanding the virulence and transmission of influenza viruses for our species. He catches both bird flu (H10N4, H5N1 et H9N2) than human influenzas (H3N2 et H1N1/pdm). Better than an intermediate host, it can be described as a springboard species for the spread of influenza from poultry to humans. Infectiologists and specialists qualify this animal as « shaker » or « mixing container »providing the perfect breeding ground for human and bird viruses to exchange genes.
This is particularly the case in a large study carried out between 2016 and 2019 on intensively farmed mink in northeast China. It showed that three quarters of the animals analyzed had at least one flu at the time of slaughter. A quarter was even infected simultaneously with a human flu virus and an avian flu virus. Everything is in place so that during these co-infections, avian flu and human flu recombine, for the worse, in the respiratory system of mink infected by both at the same time. THE « pire »that is, the appearance of a virus with bird flu mortality H5N1 and the ease of transmission of current human influenzas.
Peru says 585 sea lions and 55,000 wild birds have died of the H5N1 bird flu virus in recent weekshttps://t.co/3s4uSgsFwS pic.twitter.com/eQPqe3Uwph
— AFP News Agency (@AFP) February 8, 2023
This hypothesis becomes more and more probable as the virus H5N1 spreads. It became dominant among bird flus in 2020. Since then, it has been circulating on an unprecedented scale. However, the more it contaminates, the more the risk of a mutation which would make it contagious within the human species is exacerbated. According to the League for the Protection of Birds (LPO), 140 million farmed poultry have been slaughtered worldwide because of the virus H5N1 this season — against « only » 10 million in the 2019-2020 season.
France, United States, Peru… The virus is circulating with intensity
In France, the presence of the virus increased sharply during the winter of 2021-2022, with three times more outbreaks in poultry farms and four times more animals slaughtered than during the previous winter. In the summer of 2022, the circulation of the virus did not stop as usual in the hot season. Wild birds continued to be infected. Avian flu is now an endemic disease in France, notes the epidemio-surveillance platform in animal health.
In Europe, the virus is circulating in most countries. The United Kingdom, Poland, Hungary and Germany are particularly affected. America is also contaminated. Canada has recorded 299 outbreaks in farms. In the United States, forty-seven states have reported outbreaks in livestock or backyards. The virus is spreading to the south of the continent, in farms and among wild birds. In mid-February, Peru estimated that 55,000 birds, mainly sea birds, had died from the virus along its coasts. In Ecuador, the first human case in South America was detected in early January in a 9-year-old girl, who had been in contact with infected poultry.
Virus : Highly pathogenic avian influenza #HPAI A (#H5N1) viruses from clade 2.3.4.4
States Affected : 47
Counties Affected : 376
Reported Outbreaks : 746 (updated Feb 1, 2023)Source : @CDCgov @USDA https://t.co/uD4bSmrKKE https://t.co/l7j9nsWxbI pic.twitter.com/SaRdtojA94
— Raj Rajnarayan (@RajlabN) February 7, 2023
Logically, cases of transmission to mammals have also multiplied, noted the European Food Safety Authority. (Efsa) in September 2022. Latest example, more than 600 sea lions were found dead between January and early February on the beaches of Peru. They were probably contaminated by the many carcasses of seabirds that died of avian flu, with which they were in contact and which they may have consumed.
« Direct transmission between sea lions cannot be excludedalso note the scientists who investigated this case. Because many animals died simultaneously. » There would therefore also have been transmission between mammals. In June 2022, they are seals, on the coast of Maine in the United States, who were found dead of bird flu. Again, they could have transmitted the virus to each other and not just through contact with infected birds.
Among non-marine mammals, still in the United States, three young Montana grizzly bears were infected and euthanized in early January. They are in addition to detections in a fox and a Canada skunk the previous year. The virus has also been detected in the United States in raccoons, a coyote, black bears, inform us the Montana Park Service. In all, 121 mammals of 17 wildlife species have been infected in the United States since March 2022, reports the Ministry of Agriculture. In Europe, foxes, otters, ferrets, badgers, lynxes, but also domestic pigs have already contracted the virus, identified EFSA.
The risk is still low, but it is growing
Scientists agree that the risks of transmission from wild mammals to humans are extremely low. The inventory of the cases mentioned above all attests to the intensity of the circulation of the virus and the urgency of reducing its spread, above all in intensive farming where very large populations increase the risk of deleterious mutations and where their contact with humans are daily.
Carnivore farms, starting with mink, should be a priority. Scientists sound the alarm since at least 2009. Their diet made of raw poultry by-products constitutes a major risk of contamination by avian influenza. « To reduce the risk of emergence of new pandemic viruses, feeding mink with raw poultry by-products should not be allowed, and epidemiological surveillance for influenza viruses in mink farms should be implemented urgently », call the authors of the Chinese study in conclusion. And yet, this measure could be insufficient. Indeed, in the breeding of mink in Galicia, the contamination is probably due to contact with sick gulls. The scenario could repeat itself, with mink farms being often visited by wild birds.
Traffic in poultry farms can also be slowed down. The solutions are known and diverse, Reporterre has repeatedly cited them: less density of animals on farms, fewer farms close together on the same territory, increased genetic diversity of farmed animals, development of a vaccine, etc.
Over the past two years, the unstoppable spread of Sars-Cov2 in mink farms has already provided an example of a serious warning signal, insufficiently taken into account. All the countries in the world believed they could protect their fur production. Spain, Holland, Denmark, Greece, Ireland, Italy, United States, Canada, France, Poland: they were finally all hit one after the other without managing to stem the threat.
There’s no reason for it to be any different with the H5N1. For the moment, the pandemic risk is still low, but it is growing. Having not heard the warnings, we must now prepare for them.
