The extent of the contamination of birds and other animals by the influenza A H5N1 virus in France and around the world worries about possible human transmission. What is the H5N1 virus? What are the risks ?
The virus from influenza A (H5N1) decimates more and more wild and domestic birds in the world. ' The situation is exceptional in France by its magnitude and the period during which the detections are taking place. The health situation with regard to avian influenza highly pathogenic [influenza A H5N1 in birds] in France has deteriorated since August 2022 ' can we read on the site of the The Minister of Agriculture on February 10, 2023. The virus has also infected mammals including a weekend janvier chat in France (Deux-Sèvres) reports France info , which worries scientists. ' While most avian viruses do not infect humans, some subtypes sometimes manage to cross the species barrier: this is the case of the H5N1 virus, pathogen for humans “says the Pasteur Institute. 'Influenza A H5N1 is particularly worrying because it is an influenza virus with a very high lethality rate [in animals, editor’s note] (around 50%)” reminded epidemiologist Arnaud Fontanet to our colleagues at Parisian February 10. ' One of the characteristics of H5N1 is its strong ability to mutate but also to mix with other influenza viruses to produce new viruses, potentially more contagious, even more virulent. 'Warns Yannick Simonin, lecturer in virology at the University of Montpellier, interviewed by Le Parisien. ' Currently, the very rare cases of Human-to-human transmission of the H5N1 virus has remained episodic. However, the threat is still real: the spread of infection in birds increases the likelihood of a new influenza virus appearing in the human population 'alert the Pastor Institute . What is Influenza A H5N1?
We talk about influenza A H5N1 but we should actually talking about avian influenza A H5N1. ' Avian influenza is primarily an animal disease, infectious, highly contagious, caused by type A Influenza viruses, which can infect many species of domestic and wild birds. ' defines the CONSIDERED . According to their virulence characteristics, avian influenza viruses are classified into two categories:
► Low pathogenic viruses (LPAI)
► Highly pathogenic viruses (HPAI)
For the latter, these are then viruses of the H5 or H7 subtypes. When' infection is caused by an HPAI virus, in a susceptible species, the disease has also been called 'avian plague', avian 'flu' (term to be reserved for human disease caused by viruses of avian origin) or ' chicken flu' . Type A influenza viruses are the most important in terms of public health because they can cause an influenza pandemic in humans . A few subtypes of avian influenza viruses, mainly viruses H5N1 HP, H5N6 HP, H7N9 FP et HP, or H9N2 FP present in Asia or the Middle East, may, in rare occasions, cause serious or even fatal illnesses in humans.
The influenza A H5N1 virus was detected for the first time in a domestic goose in the Guangdong province in South China in 1996. A year later, an epidemic of H5N1 occurred in domestic poultry in Hong Kong which infected 18 humans and caused the death of 6 people. This viral disease is spotted again in 2003 in poultry first in Asia then in Europe and Africa, affecting animal species and then hundreds of human cases, causing many deaths. The H5N1 subtype has been responsible for outbreaks in French farms in 2021-2022 and 2022-2023.
No case in humans has been reported in France to date. But the H5N1 virus infected a cat at the end of January 2023 In France (Two Sevres).
► 1997. A first epidemic of the H5N1 influenza virus causes the slaughter of more than 1.5 million chickens and the death of 6 people in Hong Kong.
► February 2003. 2 deaths linked to the H5N1 influenza virus are reported in Hong Kong.
► Early 2004. Epidemic waves of H5N1 in East and Southeast Asia lead to the slaughter of at least 45 million poultry and 35 human cases including 24 deaths.
► October 2003. The H5N1 virus is detected for the first time in Europe (Belgium) in two mountain eagles smuggled from Thailand. Influenza kills 41 tigers in a zoo in Thailand fed on chicken carcasses.
► May 2005. More than 6,000 waterbirds in the Qinghai Lake National Nature Reserve in northwest China are dying from the H5N1 virus.
► January-February 2006. First human cases of H5N1 are detected outside of Asia in Turkey and Iraq.
► June-July 2007. The virus is detected on more than 200 dead wild birds in the Czech Republic, France and Germany with parallel epidemics in poultry farms in the Czech Republic and Germany.
“Like all viruses, Influenzavirus A is a parasite that must infect a host cell in order to multiply. In birds, the host cells of the Influenzavirus are mainly the cells of the digestive tract while in mammals they are mainly respiratory tract cells ' indicates the educational portal of the Toulouse Academy . The H5N1 avian influenza virus is a disease with zoonotic potential that is, it can be transmitted to humans. The main risk factor for transmission to humans is associated with direct or indirect contact with infected poultry, alive or dead. ' A few human cases of influenza A(H5N1) have been linked to the consumption of meals prepared with contaminated raw poultry blood “says the WHO.
H5N1 influenza is usually asymptomatic in wild birds but causes extremely high mortality in factory farms. In humans, the H5N1 avian influenza virus can cause:
' For avian influenza A(H5N1) virus infections in humans, current data indicate that the incubation period is 2 to 5 days on average and can reach 17 days “emphasizes the WHO.
Our immune system is not protected against H5N1 avian influenza since it does not recognize this subtype (different from classic influenza epidemics). ' this is in favor of a pandemic, a rapid and global spread of the virus “says the Pasteur Institute. 'The H5N1 subtype has a great ability to mutate over time, but also to exchange its genes with influenza viruses belonging to other infective subtypes of other species “adds the Institute. 'Influenza A H5N1 is particularly worrying because it is an influenza virus with a very high lethality rate (around 50%)' recalled Arnaud Fontanet on February 10, 2023. ' Since the initial emergence of the H5N1 virus, there has undoubtedly been a back-and-forth between domestic and wild birds, resulting in the appearance of more severe and contagious forms of the virus ' confirms Jean-Luc Guérin, unit director at INRAE and specialist in this H5N1 avian influenza interviewed by France info February 8.
There is no no vaccine against the H5N1 virus . ' There are two effective antivirals against influenza or avian viruses. They can be used in curative or preventive treatment. In the pandemic context, these antivirals are used above all to protect health personnel and professions whose maintenance of activity is essential to ensure the functioning of national structures. “notes the Pasteur Institute.
- Avian influenza: the situation in France, February 10, 2023, Ministry of Agriculture
- Avian influenza: Potentially zoonotic animal disease with essentially non-food transmission, ANSES
- Avian and other zoonotic influenzas, January 2018, WHO
- Avian influenza and the H5N1 virus, Food and Agriculture Organization of the United Nations (FAO)
- Avian Flu, Institut Pasteur
- Avian flu, Educational portal of the Toulouse Academy
- Avian influenza in 11 questions, February 9, 2021, ANSESSource journaldesfemmes.fr