Avian influenza is the disease caused in humans by influenza viruses infecting birds (avian influenza viruses, AI) which cross the species barrier and infect humans. Humans can be infected by several avian influenza viruses (particularly the H5N1, H7N9 and H9N2 subtypes).
Epidemiological situation of influenza and avian flu
Avian influenza: an unprecedented epizootic that affects almost all continents
Since October 2021, Europe is undergoingepizootic most devastating highly pathogenic avian influenza she has ever experienced. Many outbreaks, overwhelmingly due to the A(H5N1) clade 2.3.4.4b virus, have been identified in domestic poultry and wild birds, leading to the slaughter of several million birds and causing mass mortality events in L’avifauna savage. The geographical extent of this epizootic is also unprecedented, with almost all of the continents affected (in particular Europe, Asia, the Americas and to a lesser extent Africa).
In France, since August 2022, more than 300 outbreaks in livestock have been detected, more than three quarters of which are concentrated in the Pays de la Loire region in an area with a high density of poultry farms. In wild birds, the number of cases also rose sharply in France in 2022-2023 with hundreds of infected birds found dead on the territoryand an endemization of the infection of the avifauna which extends to non-migratory birds.
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Highly pathogenic H5N1 avian influenza clade 2.3.4.4b: mammals also affected
The intense and continuous circulation of these viruses in wild birds has led to the frequent introduction of the virus into the populations of poultry and captive birds, but also into regarding twenty different species of terrestrial and marine mammals, wild and domestic. Hundreds of infected mammals have been found dead or on the verge of death, with frequent detection of neurological damage. Mammal-to-mammal transmission has been suggested in seal infections in the United States (Puryear et al., 2022), from mink in spain (Agüero et al., 2023) andsea lions in Peru (référence sous BioRxiv Gamatta-Toledo et al : First Mass Mortality of Marine Mammals Caused by Highly Pathogenic Influenza Virus (H5N1) in South America (biorxiv.org)).
In France, at the end of December 2022, a chat patient tested positive for the highly pathogenic H5N1 avian influenza virus in Deux-Sèvres. ANSES was actively involved in the investigation of this case, which made it possible to identify the neighboring duck farm as being the source of the cat’s contamination. Investigations have also taken place with people who have been exposed to the infected cat, to ensure that they have not been contaminated. The first analyzes did not reveal any acute infection among the exposed people. Additional serological analyzes are in progress to confirm the absence of contamination of exposed persons.
The World Health Organization (WHO) considers that the risk of transmission to humans of currently circulating avian influenza viruses with zoonotic potential is low and no human-to-human transmission has been documented. Nevertheless, the increased frequency of transmission of these viruses to mammals of various species increases the risk of emergence of a new influenza virus better adapted to humans and capable of human-to-human transmission.
Highly pathogenic H5N1 avian influenza of clade 2.3.4.4b in humans: rare contaminations but which call for increased vigilance
Several detections of the A(H5N1) virus or the H5Nx subtype belonging to clade 2.3.4.4b have been confirmed in humans since the end of 2021 (Spain, UK, United States, China, Vietnam and Ecuador). No case has currently been diagnosed in France. The number of human cases detected remains low given the intensity of the global epizootic linked to these viruses.
The first human cases detected were identified during an active search for infection by this virus in people exposed to an outbreak in domestic birds due to this virus, while the most recent were exposed to low-income poultry. yard sick or dead. The clinical forms ranged from mild or even asymptomatic symptoms, to severe forms with admission to intensive care and death. To date, no human-to-human transmission has been demonstrated.
Recently, two human cases of A(H5N1) virus infection have been detected in Cambodia. According to theOMSthe viral strain in question does not belong to clade 2.3.4.4b, but to another clade (2.3.2.1c), endemic to Cambodia for several years.
Recommendations to follow in the event of contact or exposure to risk with wild or domestic animals
In view of the current context, Public Health France recommends:
- do not touch dead or injured animals and report them to the Departmental Office for Biodiversity or the Federation of Hunters and inform the town hall;
- protect themselves individually (gloves, mask, hand washing) in the event of contact with wild birds such as the collection of dead wild birds or during occupational exposure to birds suspected of infection;
- get vaccinated once morest the seasonal flu every year if you are a professional exposed to swine and avian influenza viruses. Simultaneous infection by an avian or swine influenza virus and a human influenza virus might in fact lead to the emergence of a new influenza virus contagious for humans;
- consult your doctor immediately in the event of symptoms (fever, cough, fatigue, breathing difficulties, neurological disorders), within 10 days of exposure to risk (contact with wild or domestic birds, with sick or dead wild mammals, or more pigs with the flu).
For healthcare professionals : it is requested to immediately report any suspected case of zoonotic influenza to the health authorities in order to classify or not the patient as a possible case and to put in place the appropriate management measures.
