Epidemiological Situation of Influenza and Avian Influenza

Avian influenza: an unprecedented epizootic affecting nearly every continent

Since October 2021, Europe has been experiencing the most devastating highly pathogenic avian influenza outbreak it has ever known. Numerous outbreaks, overwhelmingly caused by the A(H5N1) virus of clade 2.3.4.4b, have been identified in domestic poultry and wild birds, leading to the culling of several million birds and causing mass mortality events in wild bird populations. The geographic scope of this epizootic is also unprecedented, with nearly all continents affected (particularly Europe, Asia, the Americas, and to a lesser extent Africa).

In France, since August 2022, more than 300 outbreaks on farms have been detected, with more than three-quarters concentrated in the Pays de la Loire region in an area with a high density of poultry farms. Among wild birds, the number of cases also rose sharply in France in 2022–2023, with hundreds of infected birds found dead across the country, and the infection becoming endemic in wild bird populations, spreading to non-migratory birds.

Learn more:

• On the situation regarding avian influenza outbreaks in France, Ministry of Agriculture and Food Sovereignty

• On the situation at the European and international levels, EFSA (European Food Safety Authority)

• Avian Influenza Report, Santé publique France

Highly pathogenic H5N1 avian influenza of clade 2.3.4.4b: mammals also affected

The intense and continuous circulation of these viruses among wild birds has led to frequent introduction of the virus into populations of poultry and captive birds, as well as into some twenty different species of terrestrial and marine mammals, both wild and domestic. Hundreds of infected mammals have been found dead or near death, with frequent detection of neurological damage. Mammal-to-mammal transmission has been suggested in infections of seals in the United States (Puryear et al., 2022), mink in Spain (Agüero et al., 2023), and sea lions in Peru (reference on 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, in late December 2022, a sick cat tested positive for the highly pathogenic avian influenza virus H5N1 in the Deux-Sèvres department. ANSES was actively involved in investigating this case, which led to the identification of a nearby duck farm as the source of the cat’s infection. Investigations were also conducted among people who had been exposed to the infected cat to ensure they had not been infected. Initial tests did not reveal any acute infection among those exposed. Additional serological tests are underway to confirm the absence of infection in the exposed individuals.

The World Health Organization (WHO) considers the risk of human infection from currently circulating avian influenza viruses with zoonotic potential to be low, and no human-to-human transmission has been documented. Nevertheless, the increased frequency of transmission of these viruses to various mammalian species raises the risk of the 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 cases but requiring increased vigilance

Several detections of the A(H5N1) virus or H5Nx subtypes belonging to clade 2.3.4.4b have been confirmed in humans since late 2021 (Spain, the UK, the United States, China, Vietnam, and Ecuador). No cases have 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 active surveillance for infection with this virus among people exposed to an outbreak in domestic birds caused by this virus, while the most recent cases involved exposure to sick or dead backyard poultry. Clinical presentations ranged from mild or even asymptomatic symptoms to severe cases requiring admission to intensive care and resulting in death. To date, no human-to-human transmission has been identified.

Recently, two human cases of infection with the A(H5N1) virus were detected in Cambodia. According to the WHO, the viral strain involved does not belong to clade 2.3.4.4b, but to another clade (2.3.2.1c), which has been endemic in Cambodia for several years.

• Learn more about the epidemiological situation of avian influenza in Europe, ECDC (European Centre for Disease Prevention and Control)

Recommendations to follow in the event of contact or potential exposure to wild or domestic animals

Given the current situation, Santé publique France recommends:

• do not touch dead or injured animals; report them to the Departmental Office of Biodiversity or the Hunters’ Federation and notify the town hall;

• protect yourself (gloves, mask, handwashing) when handling wild birds, such as when collecting dead wild birds or during occupational exposure to birds suspected of being infected;

• get vaccinated against seasonal flu every year if you are a professional exposed to swine and avian influenza viruses. A simultaneous infection with an avian or swine influenza virus and a human influenza virus could indeed lead to the emergence of a new influenza virus that is contagious to humans;

• Consult your doctor immediately if you experience symptoms (fever, cough, fatigue, breathing difficulties, neurological symptoms) within 10 days of a high-risk exposure (contact with wild or domestic birds, sick or dead wild mammals, or pigs with influenza).