“There is no epidemic in humans.”

The highly pathogenic H5N1 avian influenza virus arrived in France in August 2021 via migratory birds. The first cases were identified in wildlife before a laying hens farm in the north was affected in November 2021. It was the first case since the winter of 2020, and since then the spread of the virus has never stopped. It gradually spread from north to southwest, then to the regions of the Great West. In the spring of 2022, outbreaks have been identified in the interior, particularly in the Dordogne and Corrèze. In total, The Department of Agriculture has identified 315 outbreaks of avian influenza in livestock since 1^any August 2021. About 28 million chickens have been slaughtered to limit the spread of the disease (between October 2021 and May 2022).

Today, the situation has calmed down, as Jean-Luc Guérin, professor of poultry farming and avian pathology, and head of the UMR Host-pathogen Interaction (IHAP) at the Veterinary School of Toulouse, explains: “ Avian influenza today’s reproduction is in sharp decline. I wouldn’t call it an extinction, but there are very few new outbreaks. In the wild, the situation is even more confusing because there are still significant deaths in certain populations of wild birds. For example, black-headed gulls are particularly affected in various parts of the territory, including the interior The Ministry of Agriculture reported 16 outbreaks identified from February to March 2023, and the epidemic is still active in nine French departments.

Claid 2.3.4.4b

The influenza viruses responsible for this systemic disease, the animal equivalent of pandemics, come from Southeast Asia. ” These are viruses of Asian lineage, descendants of the H5N1 strain that appeared specifically in 1996. Many strains are traded on a European scale and in the world, belonging to a clade that has existed since 2016 and which is the root of all our problems, clade 2.3.4.4b. »

This clade is A little or very little animal source According to Jean-Luc Guérin. In other words, their ability to cross the species barrier is limited. Influenza viruses from clade 2.3.4.4b are highly adapted to birds and are not genetically armed to infect mammals effectively. ” The risk of transmission to humans and mammals is very low “, He specifies.

Mammalian contamination explained

So how do we explain the impressive list of mammals that have been infected with avian influenza around the world? Foxes and otters in England and sea lions in Chile and Recently in New EnglandAll of these mammals have a diet that consists in part of wild birds. ” If, for example, a fox or a mink has a risk of infection in 1,000 or 10,000 if it eats a dead bird from avian influenza, if 50 birds die in a territory, then the probability of infecting a mammal is zero. But if there are a million, then there are cases. »

The only case where there can be mammalian-to-mammalian transmission is the mink breeding in Spain. ” Mink and shrews in general have cellular receptors that are more relevant to avian viruses than to humans. Therefore, they are not very representative of the general situation of mammals. »

Significant reassortment of the hemagglutinin gene, and gene segments of H5N1 strains would be required to be able to infect mammals and humans. Hemagglutinin is one of the surface proteins, along with neuraminidase, of influenza viruses that serves as a key for their entry into host cells. ” The virus is now highly adapted to birds, and for as long as it is, the risk of it adapting significantly to humans is very low. Some mutations have been observed in recent cases in mammals, but these mutations alone cannot explain anything other than a very sporadic infection. »

A small number of human cases resulted in 2.3.4.4b

In fact, cases of bird flu infection among humans are very rare. The World Health Organization recently published a report on this subject which reports 868 confirmed cases since 2003, all templates combined. Human cases from clade 2.3.4.4b can be counted on the fingers of one hand: octogenarians in England (January 2022), A 9-year-old girl in Ecuador (January 2023), Two women, ages 38 to 53, in China, a 5-year-old girl in Vietnam. The case of the girl in Cambodia that we discussed in this article is due to clade 2.3.4.4c, another branch of the historical H5N1 that circulates locally in Southeast Asia, not clade 2.3.4.4b.

Despite the sporadic human cases, several manufacturers, including Moderna and Sanofi, have It was recently said that it is ready to produce human avian influenza vaccines. So, does vaccinating humans have an interest in these panzotecs?

” no one. Today the exposure level is very lowsays Jean-Luc Guérin. In a pinch, it can be useful for very susceptible people like me, breeders or vets who really go up front in homes. But to protect them, there are other means and primarily personal protective equipment. There is no epidemic in humans, and so far these cases remain not fully confirmed. »

Vaccination of millions of poultry?

On the other hand, vaccinating poultry makes sense. This would reduce the number of circulating viral particles and slow the progression of the epidemic by reducing the appearance of reconstituted material. Influenza viruses have the peculiarity of being able to mix up their eight genetic segments. The result of this mixing is reassortment, viruses that have mosaic genomes, types of chimeras.

” The French government made decisions more than a year ago, and the roadmap drawn up by the current minister will be able to vaccinate poultry from the start of the academic year, in September. There are vaccines, but getting vaccinated against bird flu on farms is not easy. The more complicated question is that in France there are farms of ducks, chickens and turkeys and what is under discussion is: should all ducks, chickens and turkeys …? In what regions and at what time of the year? Which is complex because the dynamics of the epidemic differ across species. »

Intensive farming in question?

Southeast Asia, the birthplace of H5N1, is conducive to the emergence of infectious diseases because high-density human populations coexist with equally dense bird and pig populations. This dynamic promotes close contact between humans and animals and increases the risk of zoonotic virus transmission from one to another. But did the size of farms, especially more intensive farms, have an effect on the spread of H5N1 virus?

” In Southeast Asia, there are very large farms, but also a lot of very small farms and it’s hard to monitor that dynamic. However, on a global level, the very large increase in poultry production, especially in Asia, is not neutral, because in some ways it is fuel for the virus. This could support, computationally speaking, the likelihood of new strains emerging ”explains Jean-Luc Guérin.

But the scientist believes that cultivation techniques in Europe have very little effect on H5N1 panzootic dynamics. ” The way poultry is raised in Europe has little impact on the epidemic on a continental and transcontinental scale. The virus arrived in Europe via uninfected migratory birds in Europe. Many species are found in migratory corridors where the virus can spread easily. In Europe, wild birds can transmit the H5N1 virus to an intensive poultry farm and to a small chicken coop at the bottom of a private garden.