Since August 2021, an intense pandemic of avian influenza A H5N1 has been raging in Europe. More than 50 million poultry have been eliminated. The Centre-Val de Loire Region has not been spared since the beginning of 2023 and many outbreaks of this epizootic have been reported. Several tens of thousands of poultry had to be slaughtered. What are the risks for humans?
By Jean-Paul Briand
Viruses have genetic equipment specific to the living organisms in which they replicate, preventing their spread to other species. This is called the “species barrier”. This phenomenon makes the transmission of infectious agents from one species to another a priori unlikely. Several successive events are necessary for the jump of this barrier from an animal species to humans to cause an epidemic or a pandemic: The genetic code of the virus must be adapted to be inoculated into humans then, after overcoming the mechanisms defense, it must be able to penetrate and replicate significantly in human cells, and finally be transmitted from individual to individual.
The species jump
These are random changes to the virus or defense system that cause a ” species jump “. Some experts believe that these eventualities are remote. Others believe that the threat is very real if viral propagation is particularly intensive in the initial host. This is the case with the current highly pathogenic H5N1 avian influenza (HPAI) which kills birds. A considerable number of cases mathematically increases the probability of the appearance of mutations and of a new virus capable of contaminating the human population. For avian influenza, this risk is all the greater as its virus has a great capacity to mutate and to exchange its genes with viruses infecting other species. Events crossing the species barrier from birds to mammals have already been reported around the world.
Pigs frequently harbor human viruses. If a combination occurs between an HPAI virus and a human-derived porcine virus, human-to-human and then human-to-human transmission is possible. Which makes the Institut Pasteur researchers : « The risk of the appearance of a new virus capable of being transmitted from person to person must be taken into consideration ».
A public health issue
In the Centre-Val de Loire region, it is in the Loiret that the first outbreaks of HPAI were detected and where it seems to do the most damage. Most of the initial contaminations in breeding are linked to infected wildlife. With the spring return of migratory birds, contact between wild birds and domestic poultry will intensify. Few departments will be spared by IAHP. This is not the first time that French farms have been attacked by an outbreak of avian flu. Despite a start of an action planthe vaccination of poultry is not decisive, only their complete sheltering will avoid a hecatomb and massive operations of elimination of birds, even of preventive depopulation.
While a high level of protection is observed in factory farms, the same is not true for individuals with a few poultry. Holders of private backyards must now respect the rules from the Ministry of Agriculture, declare poultryreport any abnormal mortality and avoid mixing chickens with waterfowl in the same henhouse.
The fight against highly pathogenic avian influenza is an economic and animal health issue but, with the risk of it spreading to humans, it is also a public health issue.
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