With devastating consequences for the poultry industry, farmer’s livelihoods, international trade, and the health of wild birds, avian influenza, most commonly known as ‘bird flu’, has captured the attention of the international community over the years.
Where outbreaks occur, it is often the policy to cull all poultry, whether infected or healthy, to contain the spread of avian influenza. This represents heavy economic losses for farmers and a long-lasting impact on their livelihoods.
But poultry is not the only impacted. While they play a major role in the spread of the disease, wild birds also become victims of bird flu viruses.
Avian influenza is also a major concern for public health. Whenever avian influenza viruses circulate in poultry, sporadic cases of avian influenza in humans are sometimes identified.
What is avian influenza?
Avian influenza (AI) is a highly contagious viral disease that affects both domestic and wild birds. AI viruses have also been isolated, although less frequently, from mammalian species, including humans. This complex disease is caused by viruses divided into multiple subtypes (i.e. H5N1, H5N3, H5N8 etc.) whose genetic characteristics rapidly evolve. The disease occurs worldwide but different subtypes are more prevalent in certain regions than others.
The many strains of avian influenza viruses can generally be classified into two categories according to the severity of the disease in poultry:
- low pathogenicity avian influenza (LPAI) that typically causes little or no clinical signs;
- high pathogenicity avian influenza (HPAI) that can cause severe clinical signs and possible high mortality rates.
Transmission and spread
Several factors can contribute to the spread of AI viruses, such as:
Globalisation and international trade
Farming and sale (live bird markets)
Wild birds and migratory routes.
In birds, AI viruses are shed in the faeces and respiratory secretions. They can all be spread through direct contact with secretions from infected birds, especially through faeces or through contaminated feed and water. Because of the resistant nature of AI viruses, including their ability to survive for long periods when temperatures are low, they can also be carried on farm equipment and spread easily from farm to farm.
According to our data collected since 2005, high pathogenicity avian influenza appears to be seasonal, spread being lowest in September, beginning to rise in October, and peaking in February.
What role do wild birds play in the spread of avian influenza?
Migratory wild birds, especially waterfowls, are the natural host and reservoir of avian influenza viruses. Within their respiratory or intestinal tracts, they can carry different avian influenza virus strains. Depending on the virus strain and the species of bird, the virus can be harmless or fatal to the wild bird. When birds have little or no symptoms of the virus, it allows them to spread the viruses between neighbouring countries or over long distances, along their migratory pathways. Wild birds also play a major role in avian influenza viruses evolution and maintenance during low seasons.
The main wild species involved in the viral cycle of avian influenza are waterfowls, gulls, and shorebirds; however, the virus seems to pass easily between different bird species. Direct exposure of farmed birds to wild birds is a likely transmission route of the virus. Therefore, it is critical to limit their exposure to wild birds to lessen the risk of introduction of avian influenza into flocks.
The global impact of avian influenza
Avian influenza can kill entire flocks of birds so this causes devastating losses for the farming sectorDr. Keith Hamilton
Head of the WOAH Preparedness and Resilience Department
Avian influenza outbreaks can have heavy consequences for the poultry industry, the health of wild birds, farmer’s livelihoods as well as international trade.
might experience a high level of mortality in their flocks, with rates often around 50%
in developing countries can be significant due to the labour intensive nature of the poultry industry
may be damaged, reducing travel and tourism in affected areas
are often culled to contain outbreaks, resulting in risks to animal and human welfare, protein wastage and economic impacts
The presence of HPAI
restricts international trade in live birds and poultry meat This can heavily impact national economies
Impact on animal health, including wild birds
With severe mortality rates, avian influenza can heavily impact the health of both poultry and wild birds. Often considered mainly as vectors of the disease, wild birds, including endangered species, are also victims. The consequences of AI on wildlife could potentially lead to a devastating effect on the biodiversity of our ecosystems.
In addition, avian influenza can also cross the species barrier and infect mammals, such as rats, mice, weasels, ferrets, pigs, cats, tigers, dogs and horses.
Public health risk
The transmission of avian influenza from birds to humans is usually sporadic and happens in a specific context. People who are in close and repeated contact with infected birds or heavily contaminated environments are at risk for acquiring avian influenza.
However, due to ongoing circulation of various subtypes, outbreaks of avian influenza continue to be a global public health concern.
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These reports provide an update of the high pathogenicity avian influenza situation at both global and regional levels, according to the information submitted by countries through the World Animal Health Information System (WOAH-WAHIS).
Surveillance and reporting of outbreaks
The first line of defense against avian influenza is the early detection and reporting of disease outbreaks to allow a rapid response. Putting in place accurate warning systems is thus essential to efficiently prevent and control the disease.
Because of its capacity to rapidly spread across regions, timely reporting of cases is key to enable countries to anticipate and get prepared for potential new outbreaks of avian influenza.
It is an WOAH-listed disease. As such, national Veterinary Authorities must report:
- all high pathogenicity avian influenza viruses, irrespective of their subtypes, detected in birds (domestic and wild)
- all low pathogenicity viruses, in domestic or captive wild birds, that have proven natural transmission to humans with severe consequences.
When LPAI viruses are detected in wild birds, countries can voluntarily report them through the voluntary report on non WOAH-Listed diseases in wildlife. In addition, countries may self-declare the absence of high pathogenicity avian influenza from their territory on a voluntary basis.
Prevention of avian influenza at its animal source
Strict biosecurity measures and good hygiene practices are essential to prevent avian influenza outbreaks, because of the resistance of the virus in the environment and its highly contagious nature.
Relevant measures notably include keeping poultry away from contact with wild birds, ensuring good hygiene in poultry housing and equipment and reporting bird illnesses and deaths to the Veterinary Services.
Control strategies and compensation for farmers
When an infection is detected in poultry, a policy of culling infected animals and the ones in close contact is normally used in an effort to rapidly contain, control and eradicate the disease.
Selective elimination of infected poultry, movement restrictions, improved hygiene and biosecurity, and appropriate surveillance should result in a significant decrease of viral contamination of the environment. These measures should be taken whether or not vaccination is part of the overall strategy.
Systems of financial compensation for farmers and producers who have lost their animals as a result of mandatory culling ordered by national Veterinary Authorities vary around the world; unfortunately, they may not exist at all in some countries. The WOAH encourages its Members to develop and propose compensation schemes because they are a key incentive to support early detection and transparent reporting of animal disease occurrences, including avian influenza.
The use of vaccination
Under certain specific conditions, vaccination of poultry may be recommended. However, this measure alone should not be considered a sustainable solution to control avian influenza. It must be used as part of a comprehensive disease control strategy, in addition to other health measures. Its overall goal: to help control the disease until the virus can be eliminated by other methods. Indeed, despite its benefits, vaccination can hide inapparent infections and compromise the surveillance of circulating strains.
The decision to set up vaccination plans rests with the Veterinary Authority of each country. It must be based on a risk analysis at regional and national level and in consideration of the international context, potential economic consequences of current outbreaks, and the capacity of the Veterinary Services to conduct an effective vaccination campaign.
Any decision to use vaccination must include an exit strategy, i.e. conditions to be met to stop vaccination.
One Health approach
Because of the potential risk on human health and the far-reaching implications of the disease on the health of wild bird populations, avian influenza should be tackled under a One Health approach. Besides the grave impacts of the virus on poultry, AI can also devastate wild birds populations, threatening the sustainability and biodiversity of our ecosystems.
It is therefore critical that the international community work together across sectors to combat the spread of this disease. The WOAH is closely working with the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) to monitor the evolution of the disease at the human-animal-environment interface, in line with a One Health approach.
OFFLU: WOAH/FAO global network of expertise on animal influenza
Since its launch in 2005, the OFFLU network has continuously worked to reduce the negative impacts of animal influenza viruses, including avian influenza, by promoting effective collaboration between animal health experts and the human health sector.
The objectives of OFFLU are to:
- exchange scientific data and biological materials (including virus strains) within the network, and to share such information with the wider scientific community
- offer technical advice and veterinary expertise to Members to assist in the prevention, diagnosis, surveillance and control of avian influenza
- collaborate with the WHO to contribute to the early preparation of human vaccines against seasonal flu
- highlight avian influenza research needs, promote their development and ensure coordination.
WOAH global scientific network
Through its global network of more than 300 Reference Laboratories and Collaborating Centres (collectively, ‘Reference Centres‘) the WOAH provides policy advice, strategy design and technical assistance for the diagnosis and control of avian influenza.
Centres of expertise and standardisation of diagnostic methods, their goal is to provide the required technical and scientific expertise and to form opinions regarding the monitoring, control, and eradication of these viruses.
They also propose scientific and technical training for Members and coordinate scientific and technical studies in collaboration with other laboratories and organisations.
The resources on avian influenza found here, developed by the WOAH and our partners, are freely accessible and available to everyone for downloading and distribution.
Also known as bird flu, avian influenza (AI) is a viral disease affecting poultry and wild birds, often resulting in heavy animal health and economic consequences. While AI viruses are highly species-specific, on certain occasions they have crossed the species barrier and have been isolated from mammalian species, including humans.
These viruses are classified into subtypes based on two surface proteins, the hemagglutinin (HA) and neuraminidase (NA). For example, a virus that has HA 7 protein and NA 9 protein is designated as subtype H7N9. At least 16 hemagglutinins (H1 to H16), and 9 neuraminidases (N1 to N9) subtypes have been found in viruses from birds, while two additional HA and NA types have been identified only in bats.
Regular global situation reports are developed by WOAH experts, based on the data reported by countries through the WOAH World Animal Health Information System (WAHIS). They are publicly available:
Consult the latest situation report
Access OIE-WAHIS for latest information
While it is likely that international trade, farming practices and migratory wild birds have contributed to the spread of avian influenza, the current wide range of avian influenza subtypes circulating shows an ever-evolving complexity in both virus genetics and spatiotemporal distribution. This might be explained by multiple reassortments with low pathogenicity viruses circulating in wild birds.
The dynamic of the spread of avian influenza viruses is complex and difficult to predict. However, the data received by the WOAH over the last 15 years helps to reveal a seasonal pattern: the number of outbreaks of HPAI usually is lowest in September, begins to rise in October, and peaks in February. Several factors can influence this dynamic, such as the wild bird migration pattern, unregulated trade, farming systems, biosecurity and immunity status.
At local level, as the avian influenza viruses can survive for long periods in the environment, they can be easily transmitted from farm to farm by the movement of infected animals, as well as contaminated boots, vehicles and equipment if the adequate biosecurity measures are not implemented. During the Northern Hemisphere winter, the wild bird movements may increase, and lower temperatures may facilitate the environmental survival of AI viruses, increasing exposure of infection in poultry. Additionally, the mixing of wild birds from different geographic origins during migration can increase the risk of virus spread and genetic reassortment resulting in changes in viral properties.
Sustaining veterinary activities amid the COVID-19 pandemic is essential in avoiding the detrimental impacts of other diseases, including animal diseases, which could further exacerbate the current health and socio-economic crises.
Despite the challenging context, Veterinary Authorities in the affected countries have responded to contain AI outbreaks in poultry with control measures, heightened surveillance, and biosecurity recommendations to poultry owners.
The transmission of avian influenza from birds to humans is rare and usually occurs when there is close contact with infected birds or heavily contaminated environments. Indeed, between 2005 and 2020, 246 million poultry died or were culled because of avian influenza. In the same period of time, human have occasionally been infected with subtypes H5N1 (around 850 cases reported), H7N9 (around 1,500 cases reported), H5N6 (around 50 cases reported) and sporadic cases have been reported with subtypes H7N7 and H9N2.
Following the evolution of the global situation, the WHO Global Influenza programme regularly releases risk assessments on influenzas at the human-animal interface.
Moreover, there is no evidence to suggest that the consumption of poultry meat or eggs could transmit the AI virus to humans. However, as a general precautionary measure, animals that have been culled as a result of the implementation of control measures in response to an AI outbreak should not enter the human food and animal feed chain.
It is essential for poultry farmers to maintain biosecurity practices to prevent the introduction of the virus. Some of these measures include:
prevent contact between poultry and wild birds
minimise movements around poultry enclosures
maintain strict control over access to flocks by vehicles, people and equipment; clean and disinfect animal housing and equipment.
avoid the introduction of birds of unknown disease status
report any suspicious case (dead or alive) to the veterinary authorities
ensure appropriate disposal of manure, litter and dead animals
vaccinate animals, where appropriate.
As soon as detected or suspected, avian influenza should be brought to the attention of Veterinary Authorities in accordance with national regulations. In an effort of surveillance and transparency, these authorities are required to timely report of high pathogenicity avian influenza viruses detected in both poultry and non-poultry species including wild birds, and low pathogenicity avian influenza viruses that have proven natural transmission to humans with severe consequences to the World Organisation for Animal Health. In addition, LPAI viruses in wild birds can be reported on a voluntary basis, through the voluntary report on non OIE-Listed diseases in wildlife.
Notifying the disease occurrences helps to better monitor, understand and control it.
To support countries in the fight against this disease, the WOAH developed international standards on avian influenza, which provide the framework for the implementation of effective surveillance and control measures.
As part of the OFFLU network (OIE/FAO) of experts on animal influenzas, the OIE and its partners work together to assess the risks of avian influenza viruses and provide the needed guidance and recommendations to the international community.
Additionally, the OIE World Animal Health Information System (WAHIS) provides a window on the disease situation worldwide. Through its online platform, the system disseminates information about AI outbreaks and sends alerts on events in real time. This allows the international community to follow the evolution of the virus and, therefore, to implement appropriate and timely responses.