2023-06-02 08:48:02
What is avian influenza?
Avian influenza is a highly contagious animal disease caused by influenza type A viruses, which can affect very numerous species of wild birds, pets and those in zoological parks.
There are two categories of viruses according to their virulence characteristics for birds:
In its highly pathogenic form, the disease spreads very quickly among birds and can have significant consequences both on farms and for wildlife. It can cause very high mortality in certain species.
What is the current situation in France?
In France, since 2015, highly pathogenic viruses have been the cause of increasingly large-scale epizootics, particularly in waterfowl farms in the south-west of France. These episodes, which for the most part also affected other European countries, led to a number of poultry slaughtered never before reached in France or in Europe.
What viruses are currently circulating?
The highly pathogenic strain A (H5N1) of the avian influenza virus has been in the news since 1997, due to significant outbreaks in Asia among farmed and wild birds and its zoonotic potential, that is to say its ability to infect humans under certain conditions.
Since 2003, this strain has spread worldwide and is still circulating today. H5N6, H5N5 or H5N8 viruses derived from them have also spread in recent years. The latter are of concern due to their degree of virulence and their wide distribution, not only among poultry but also among wild birds.
Beyond birds, are other animals affected?
Certain strains of the virus can infect mammals such as pigs, ferrets, mink, foxes and even cats. They can cause respiratory or neurological symptoms in these species.
When a bird virus infects a mammal (human or animal), certain mutations can be selected in the virus and promote its multiplication or transmission in this new host species.
Can humans be contaminated?
Avian influenza is a disease caused by zoonotic potentialThe virus can therefore, under certain conditions, be transmitted to humans. This transmission can take place in the absence of wearing personal protective equipment during frequent and/or prolonged contact with animals infected with the virus, whether or not they show symptoms.
The virus then causes symptoms in humans that most often resemble a common cold or flu, which can in extremely rare cases quickly worsen due to severe respiratory problems. Human-to-human transmission is extremely rare. To date, no human cases have been observed in France. However, it is recommended that people who have been in contact with infected poultry and who then show respiratory signs report this to their doctor.
Finally, the existence of a simultaneous infection by an avian influenza virus and by a human influenza virus in a human being or in a pig could promote reassortment. It is a mixture of genetic material between the two viruses, which can lead to the emergence of a new virus that is highly contagious for humans. This is why people in contact with infected birds or pigs are advised to be vaccinated against seasonal flu.
How is avian influenza transmitted?
Farmed poultry can be contaminated by infected wild birds or, during an epizootic, by other domestic birds, whether they are breeding or recreational (farmyards, ornamental birds, decoys used for waterfowl hunting). A large number of bird species can become infected.
Many factors can contribute to the spread of avian influenza viruses:
THE migratory movements wild birds, breeding practices,THE flow of people and materials within production sectors or between hobby poultry and farms.
The transmission between birds can be direct, through close contact between individuals – respiratory secretions, feces – or indirect, through exposure to contaminated materials or media: food, water, equipment, feathers, dust, or clothing. The virus enters the body of poultry by the respiratory route or by the digestive route.
How does avian influenza manifest?
Depending on the modalities of exposure and the virulence of the viral strain, the incubation period of the disease can vary. 1 to 3 days at individual level and expand up to 14 days at the level of a flock of poultry. Symptoms in birds are divers : nervous disorders (paralysis, convulsions, loss of balance), respiratory disorders, digestive disorders, head edema, drop in the number of eggs laid and mortality, which in the most serious cases can appear almost without prior symptoms.
The disease can also be asymptomatic and only detectable by laboratory analyzes or manifest in moderate forms: reduced appetite, reduced egg laying, more or less discreet respiratory signs, etc.
Where is avian influenza present?
Avian influenza affects the whole world with different virus strains more present in some parts of the world than others. Since the 1950s, numerous more or less serious episodes linked to highly pathogenic avian influenza viruses have been reported around the world in poultry farms or in wild birds.
Is there a treatment for avian influenza viruses?
Vaccines are available around the world, but only one currently has marketing authorization in Europe because vaccination, with very rare exceptions (zoo animals), was until recently prohibited. European regulations were modified in 2023 to allow States to decide to launch a vaccination campaign if the health situation justifies it. It authorizes the vaccination of poultry under certain conditions, including the establishment of surveillance of vaccinated farms, so as to guarantee the absence of inapparent infection in these animals. In fact, the available vaccines reduce but do not completely eliminate the excretion of the virus by birds which, even if vaccinated, could still be infected. It is therefore important to define monitoring programs for future vaccinated herds, to detect possible circulation of the virus. Specific validated tests will be used to distinguish, among vaccinated poultry, those which may be infected.
To more easily meet these requirements, new generations of vaccines and new detection techniques are already available or under development. It is also important to have vaccines adapted to the avian influenza viruses circulating within each species of domestic birds at a given period. Several vaccines having proven their protective effect against circulating viral strains have thus received temporary authorization of authorization (ATU) in France for use from 2023, in order to quickly have vaccine solutions available.
How to fight disease on farms?
The fight against disease today is essentially based on:
strengthening biosecurity in periods of risk, with sheltering birds and strengthening hygiene measures at the entrance to farms (cleaning equipment, changing work clothes, washing hands, etc.), to avoid contamination from wild birds, or transmission between farms;
monitoring of poultry farmswith the aim of early detection and elimination of infected poultry as quickly as possible.
In times of epizootic, depopulation measures of the most affected areas, so as to limit the number of susceptible poultry present and likely to contribute to the spread of the disease.
What is ANSES’s role in preventing the spread of avian influenza?
The Anses is national reference laboratory (NRL) to carry out in particular all the confirmatory analyzes and methodological developments necessary for the diagnosis of avian influenza. The NRL regularly checks skills and manages the network of approved or recognized veterinary laboratories for first-line diagnosis.
ANSES intervenes with the health authorities in the management of epizootics, particularly through epidemiological surveys to identify the causes of influenza outbreaks and to limit the risks of spread. It also conducts experiments intended to evaluate the effectiveness of certain management approaches: experimental evaluation of the duration of slurry sanitation, contribution to the study of the effectiveness of vaccine candidates for waterflies, monitoring of viral persistence on landfill sites.
The Agency conducts research work focused on ducks, a potential relay for transmission to other poultry species, and on the inter-species transmission of avian influenza viruses. This work ranges from the development of methods for detecting the virus in farms and the environment, to the search for solutions to reduce the risks of introduction and dissemination of viruses.
In the event of infection observed in areas close to France, or in the event of mortality of wild birds affected by avian influenza in our country, ANSES assesses the risks of introduction and spread of the disease in French poultry farms. It provides scientific advice to support health authorities in disease management. It intervenes in coordination with the National Reference Centers responsible for the characterization of human influenza viruses, in interaction with Public Health France and the regional health agencies competent in the surveillance and management of possible transmissions to humans, to analyze the risks that influenza viruses detected in animals may represent for humans.
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