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Updated on 11/02/2021

Avian influenza in six questions

Keywords : Avian influenza, Animal diseases, Zoonosis, Animal health, H5N1 (Bird), Bird flu

Avian influenza is a highly contagious viral infection occurring in wild and domestic birds. Wild bird migration periods and movements have an impact on the level of risk of influenza virus transmission from wildlife to poultry farms. Liable to cause extremely high animal mortality and therefore major economic losses, some avian influenza viruses can be transmitted to humans under certain conditions. Here we present the profile of a highly contagious disease and describe the work of ANSES, a key player in preventing the spread of high-pathogenicity avian influenza viruses.


1/ What is avian influenza?

2/ How is avian influenza transmitted?

3/ What are the symptoms of avian influenza?

4/ Where is avian influenza found?

5/ What is being done to prevent and control avian influenza viruses?

6/ What is ANSES' s role in limiting the spread of avian influenza?


1/ What is avian influenza ?

Avian influenza is a highly contagious animal disease caused by influenza A viruses, which can infect many wild and domestic bird species. Avian influenza viruses are classified based on the characteristics of two of the proteins in the viral envelope (external structure of the virus): hemagglutinin (16 subtypes numbered from H1 to H16 in birds) and neuraminidase (nine subtypes numbered from N1 to N9); all combinations of these two proteins are theoretically possible. There are also two categories of viruses depending on their virulence characteristics: low-pathogenicity viruses (LPAI) and high-pathogenicity viruses (HPAI). All of the latter belong to subtypes H5 or H7.

In its highly pathogenic form, the disease rapidly spreads in birds and causes very high mortality, generating considerable economic losses for the poultry sector. Some strains of the virus can also infect certain mammals such as pigs, cats and ferrets and, in certain conditions, can be transmitted to humans. Avian influenza is therefore a disease with zoonotic potential.

2/ How is avian influenza transmitted ?

Domestic poultry are mainly contaminated by infected wild birds or, in the event of an outbreak on a farm, by other infected poultry farms. A wide variety of wild species, especially ducks and geese, whether migratory or not, can potentially become infected.

Infected poultry with or without symptoms can contaminate humans if the viral strain has characteristics of human transmission. Multiple factors can contribute to the spread of these viruses: globalisation and international trade, farming practices, and migratory movements of wild birds.

Did you know?

Influenza A viruses have a high level of “plasticity” and continuously evolve by exchanging their genes or acquiring mutations: all of these events may enable these viruses to infect new species, “circumvent” the animal or human host’s immune defences, or become more virulent.

Transmission between birds can be direct due to close contact between individuals – respiratory secretions, faecal matter – or indirect via exposure to contaminated materials – contaminated feed, water, equipment or clothing. The virus enters the bodies of poultry through the respiratory tract or digestive tract.

3/ What are the symptoms of avian influenza ?

Depending on the exposure conditions and the virulence of the viral strain, the disease’s incubation period can range from one to three days within an individual; within a poultry flock, it can be as long as 14 days. The disease causes a variety of symptoms in birds: nervous disorders (paralysis, convulsions, loss of balance), respiratory disorders, digestive disorders, swelling of the head, or a decrease in the number of eggs laid. The disease can also be inapparent, in which case it can only be detected via laboratory analyses. There are also more moderate forms presenting as a decrease in appetite, reduced laying performance, more or less discrete respiratory signs, etc.

Did you know?

When the disease occurs in birds, the term avian influenza is used. The term avian flu is used in particular to refer to human disease caused by avian influenza A viruses with zoonotic potential.

4/ Where is avian influenza found?

Avian influenza is found worldwide with various viral strains occurring more frequently in certain parts of the world. Since the 1950s, several outbreaks of varying severity caused by high-pathogenicity avian influenza viruses have been reported on poultry farms around the world. From 1997 to the 2010s, there was much talk about the highly pathogenic avian influenza virus A (H5N1) strain, due to the emergence of large outbreaks in Asia in domestic and wild birds and because of its zoonotic potential. In recent years, H5N6, H5N5 and H5N8 viruses have been widespread and have raised concerns, due to their degree of virulence and their wide distribution, not only in poultry but also in wild birds.

5/ What is being done to prevent and control avian influenza viruses ?

There is no specific treatment for the disease. The vaccination of animals is currently difficult from a technical standpoint. This is because it is necessary to ensure that the vaccine is suited to the viruses found in the region in question and that vaccination will not encourage the inapparent circulation of the wild virus in vaccinated birds. For European Union Member States, vaccination is prohibited and disease control is based on the strengthening of biosecurity in high-risk periods, to prevent contamination from wild birds and transmission between farms; it also relies on the monitoring of poultry farms, with a view to early detection and culling of infected or potentially infected poultry.

The monitoring of this disease is regulated at the international level. In France, it is classified in Category 1, with mandatory disease control and notification managed by the State. There is a permanent monitoring and diagnostic network. It calls on farmers, state-mandated veterinarians, farm technicians, Departmental Directorates for the Protection of Populations, employees of the French Biodiversity Agency, ornithologists, veterinary diagnostic laboratories, and the National Reference Laboratory.

6/ What is ANSES’s role in limiting the spread of avian influenza ?

  • The ANSES National Reference Laboratory: a key diagnostic player

A network of veterinary laboratories coordinated by the ANSES National Reference Laboratory (NRL) for avian influenza based at the Ploufragan site (Ploufragan-Plouzané-Niort laboratory) operates on a permanent basis to rapidly carry out all analyses required to diagnose infections. Whenever the disease is suspected, on the basis of official clinical suspicion criteria, standardised samples are collected and immediately sent to the official veterinary laboratories, which perform RT-PCR screening tests. ANSES’s laboratory then performs confirmatory analyses if a positive result is obtained with these tests. The laboratory also participates in annual interlaboratory proficiency tests at European level and organises their equivalent in France so as to guarantee the operational capacity of the veterinary screening laboratories. Moreover, the NRL develops new analytical methods, has a strain library that it adds to on a regular basis, and conducts in-depth investigations aiming to characterise isolated strains. ANSES’s laboratory also contributes to the international pooling of data on the circulation of avian influenza virus strains, as part of OFFLU (joint OIE-FAO global network of expertise on animal influenza).

  • Research activity focused on ducks, which play a potential role in transmission to other poultry species

During the most recent outbreaks in France (winters of 2015-2016 and 2016-2017), the Ploufragan-Plouzané-Niort laboratory conducted research on the virus’s persistence in duck faeces and on the development of a method for its detection on farms and in their environments. The goal was to detect the most contaminated areas and equipment and assess the effectiveness of the cleaning and disinfection measures taken, before any resumption of activity or reintroduction of animals into farms. Epidemiological investigations were conducted in the field, in the various affected départements, in collaboration with the Departmental Directorates for the Protection of Populations. During this period, the Agency was also involved in studying the efficacy of avian influenza vaccines.

The French outbreak of high-pathogenicity avian influenza in winter 2016-2017 heavily impacted the fattened goose and duck production sector as well as the entire French poultry sector. An in-depth study of the characteristics of the avian influenza viruses detected during this outbreak in terms of genetic variability, host adaptation and transmission capacity seems essential, to improve responsiveness and adapt control measures in the event that a new high-pathogenicity avian influenza virus emerges. To address these issues, the PREDYT project financed by the FRIA 2019 fund has been under way since October 2019 and involves three complementary components calling on the epidemiological and virological expertise of its partners: the ANSES Ploufragan-Plouzané-Niort laboratory (coordinator), the Veterinary School of Toulouse and the INRAe Molecular Virology & Immunology Unit.

Since December 2017, the Ploufragan-Plouzané-Niort laboratory has been involved in an experimental study dealing with the circulation of low-pathogenicity avian influenza viruses in flocks of ready-for-gavage ducks in France. The goal of this study is to analyse and describe the viral strains circulating in populations of fattened geese and ducks which, since they show few or no symptoms when infected with avian influenza viruses, can contribute to the spread of the virus on farms. This study is also seeking to find solutions with all of the stakeholders involved, to reduce the risks of introduction and spread of low-pathogenicity avian influenza viruses on farms.

At international level, the Agency’s scientists act as experts or consultants for the European Commission, the World Organisation for Animal Health (OIE), the Food and Agriculture Organisation of the United Nations (FAO) and the European Food Safety Authority (EFSA). Its experts also participate in the standardisation work of AFNOR, the OFFLU network (OIE/FAO), and the European Pharmacopoeia.

  • Assessment of the risks of introduction and spread of high-pathogenicity avian influenza and epidemiological news relating to avian influenza

When infections are observed in areas near France, and when wild birds die from avian influenza in our country, ANSES receives regular requests from the Ministry of Agriculture to assess the risk of introduction and spread of the disease on French poultry farms.

Concerning the risk associated with wildlife, during the outbreak due to an H5N8 virus in 2016-2017, ANSES published two opinions (Adjustment of risk levels, Assessment of risk levels) that provided the health authorities with criteria for raising or lowering the level of risk of disease transmission based on the migration period of wild birds, the geographic areas covered by these birds and the number of poultry farms in these areas. These opinions were prepared by multidisciplinary expert committees made up of epidemiologists, virologists and ornithologists. The Ministry of Agriculture can refer to these two opinions to adapt the risk of introduction of avian influenza in France based on the epidemiological situation worldwide and in Europe. This situation is updated on a regular basis by the epidemiological surveillance platform for animal health with input from the ANSES National Reference Laboratory for avian influenza.

In December 2020, new outbreaks of highly pathogenic avian influenza H5N8 appeared in the Landes département of France and have spread there as well as in three neighbouring départements (Gers – Hautes-Pyrénées – Pyrénées Atlantiques). Faced with this epizootic, ANSES provides scientific and technical support as well as opinions concerning both measures to control the disease in the south west of France  (see our SCIENTIFIC AND TECHNICAL SUPPORT NOTE and the ANSES Opinion) (in French) and the monitoring and transporting of decoys for waterfowl hunting and game release (see the SCIENTIFIC AND TECHNICAL SUPPORT NOTE and the ANSES Opinion ) (in French).