The Covid-19 makes us forget that another pandemic is breaking out all over the world. Avian influenza – commonly known as avian influenza – circulates massively in the shadow of poultry farms. At the end of November, a first outbreak was detected in France in a laying hen farm in Warhem (North) after an “observation of abnormal mortalities”, according to the Ministry of Agriculture. The government had however anticipated by ordering, a few weeks earlier, the confinement of birds throughout the territory due to the multiplication of cases outside our borders among migratory birds. The trauma of the winter 2020 epizootic has not faded. The disease had by then spread like wildfire in the farms of the South-West and was only stopped at the cost of the slaughter of more than 3.5 million animals. The dreaded scenario could happen again.
Since May, outbreaks have been detected in more than 40 countries. And nearly 16,000 cases in domestic and wild birds have already been reported in October alone, “which suggests an increased risk of circulation of the virus,” worries the World Organization for Animal Health. In addition to the economic cost for professionals in the sector, the prevalence of the virus worries scientists, who fear an overflow into the human population. This is what happened last year. In December, at a gigantic farm near the city of Astrakhan in southern Russia, 101,000 chickens passed out before they died. The cause is a relatively new strain, H5N8, which forced the authorities to hastily slaughter 900,000 other birds as a preventive measure. And the case did not end there: of the 150 workers on the farm, seven were found to be carriers of the disease. These are the first known cases of transmission of H5N8 to humans.
According to scientists, there are a total of eight variants of avian influenza, all of which can infect or even kill humans. Considered to present risks of greater severity than Covid-19, they circulate regularly in factory farms around the world, going almost unnoticed. This year, a wind of concern has been blowing since mid-October from China, where the H5N6 strain, first identified seven years ago, has infected 50 people – most of them workers in poultry farms. . This suggests that H5N6 is gaining ground, mutating, and could become extremely dangerous. So much so that the Chinese Center for Disease Control and Prevention calls it a “serious threat.”
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Adaptation or recombination: the two feared scenarios
“In the short term, there is no zoonotic risk, tries to reassure Jean-Luc Guérin, professor at the National Veterinary School of Toulouse, specialist in poultry farming and avian pathology. This form of influenza is perfectly suited to birds, particularly to ducks. However, if we allow this virus to thrive for years in farms, we run the risk of seeing it become dangerous for humans “. A point of view shared by Hervé Fleury, emeritus virologist at the CNRS: “In the event of infection in humans, a mortality rate of around 40 to 50% is observed. For the moment, avian influenza does not exist. has no pandemic capacity, and human-to-human transmission remains very low, without our knowing the exact reason. ”
The researcher fears two scenarios: an adaptation of the H5N8 strain to humans by dint of circulating within farms; or recombination of the virus with H3N2, human influenza. The case of influenza A (H1N1) in 2009 remains emblematic in this respect, since it has turned out to be a recombination of three types: avian, human and swine! “It is a mosaic chimera which has adapted to the ecosystem in which it was evolving”, explains François Renaud, research director at the CNRS and biologist in the evolution of infectious diseases.
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Capacities for evolution and mutation which, according to scientists, should make us rethink the concept of intensive breeding: its principle promotes the circulation and mutation of viruses. “We must take into account the fact that the H5N8 virus will undoubtedly settle for many years to come. This danger is a real challenge for our outdoor poultry production systems,” Jean-Luc Guérin still judges. So how can we hope to contain this epizootic? And the next ones? The question is worth the answer. In its hypotheses on the origins of the Covid, the WHO still suspects the coronavirus to come from giant farms in Southeast Asia. It was already there, in these buildings crowded with poultry, that a certain … H5N1 had appeared in the mid-2000s.
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