Avian influenza, also called bird flu, is a type of virus found in birds. Many different strains exist and some zoonotic strains can infect and even kill humans. The 1918 Spanish Flu pandemic was in fact an influenza A(H1N1) of avian origin that infected 500 million people around the globe. However, since then, there’s been no evidence of sustained human-to-human spread and in the past decades human infections have been sporadic, the most recent reports to the World Health Organization (WHO) were in November 2020, when H5N6 and H9N2 avian influenza viruses were detected in two persons in close contact with live poultry.

Avian influenza are RNA viruses, so mutate and evolve more quickly than DNA viruses, thus heightening the chance of increased adaptation to mammals, including humans. The Tripartite – FAO, the World Organisation for Animal Health (OIE) and WHO – work together to conduct monitoring and risk assessment on a regular basis. They also provide data for WHO’s seasonal vaccine composition meetings, a direct support to pandemic preparedness. The three organizations also recently published a tool for national joint, multi-sectoral risk assessment (JRA) that can be used by countries to assess zoonotic health risks at the animal-human-environment interface and guide risk management.

Since its first known emergence in Asia in 1996, several intercontinental avian influenza epidemics have occurred. Although poultry trade remains the most important risk factor for introduction and local spread of avian influenza viruses, long-distance spread is often facilitated by wild birds migrating, with deadly impact on domestic and wild bird populations.

Avian influenza viruses are numerous due to their high spontaneous mutation rate and their capacity to ‘reassort’ with genetic material of other avian influenza viruses to ‘give birth’ to new virus strains. The current classification of subtypes is based on the Hemagglutinin (H) and Neuraminidase (N) genes. Currently, 18 hemagglutinin and 11 neuraminidase subtypes are known to exist in nature, meaning more than 100 combinations based on just these two genes are possible. Today, the H5Nx, H7Nx, and H9Nx subtypes are closely monitored by the scientific community for zoonotic potential, particularly H5N1, H5N6, H7N9, H9N2 subtypes.

Avian influenza types are also classified as low or highly pathogenic avian influenza (LPAI or HPAI). This denomination primarily refers to their potential to kill chickens, and is not related to their ability to infect other animal species or humans. Usually, LPAI viruses cause no or few clinical signs in poultry and disease is less severe or acute than with HPAI viruses, thus economic damage is less intense. However, LPAI viruses can sometimes mutate into an HPAI virus.

There is currently an increased number of HPAI epidemics ongoing in Europe and Asia as well as emergence of reassortant strains (those combining genetic material from different avian influenza viruses) which are affecting poultry and wild birds. In October and November 2020, FAO began to alert animal health authorities in countries at high risk, and continues to provide advice and recommended actions.

The most prevalent HPAI strain since October 2020 is H5N8, affecting more than 30 countries or administrative territories from Ireland to Japan, with more than 1 300 events officially reported events in poultry and wild birds. As of now, no confirmed detections have been reported in Africa or the Americas, although another strain (H5N1 HPAI) has recently been reported in poultry in Senegal.

The H5N8 avian influenza virus currently circulating in Asia, Middle East and Europe has not caused any human infections to date. However, its zoonotic potential should not be ignored, as if an avian influenza virus acquires the ability for sustained human-to-human transmission, the pandemic threat becomes very real very quickly.  (See question 7 and 8 for how people and authorities can minimise the risks).

Analyses of gene sequences of the virus strains detected during outbreaks allow scientists to reconstruct the history of virus circulation and evolution across continents. According to recent genetic analyses, although the clinical picture in affected domestic and wild bird populations is similar, the H5N8 virus strain currently circulating in Eastern Asia is genetically different to the one circulating in Europe. This means that both epidemics developed independently at the same time.

FAO is closely monitoring avian influenza spread worldwide and keeps a database (EMPRES-i) to record events in poultry, wild birds and humans reported by different official sources, including OIE and WHO. Detailed information about the current situation can be found in the Global Avian Influenza Virus with Zoonotic Potential Situation Update, the Sub-Saharan Africa HPAI Situation Update and the H7N9 Situation Update. 

The spread of avian influenza over long distances is facilitated by wild bird migrations. Wild birds are the natural reservoir for avian influenza viruses and every year a massive number of wild birds migrate westwards from Central Asia during August-December in search of feeding grounds in warmer locations, stopping over at multiple resting sites in the Middle East and Europe. Certain species also extend their range to southern latitudes, including sub-Saharan Africa. 

The more species of wild bird carrying the virus, the more migratory flyways along which the virus can spread. The significant congregations of wild birds in Central Asia allow for mixing of species and gives opportunity for avian influenza viruses to circulate, persist, and evolve. Ducks in particular play a key role in their spread as they can shed the virus without showing any clinical signs. Countries along these flyways are at higher risk of avian influenza introduction, especially if biosecurity in poultry farms is weak or if there is contact between wild and domestic birds in situations such as free-grazing poultry.

Once introduced in a country or region, avian influenza can quickly spread through poultry trade within and between countries, especially through informal trade which is less controlled and where biosecurity practices are poor.

While the COVID-19 situation complicates prevention and control efforts, countries and the international community must remain vigilant as avian influenza has pandemic potential and its economic consequences are significant.  FAO recommendations include: increased surveillance efforts in higher-risk areas, immediate testing of sick or dead poultry or wild birds, and good biosecurity measures, including limiting direct and indirect contact between domestic poultry and wild birds. 

The ongoing COVID-19 pandemic has resulted in many practical and financial challenges for the public and animal health sectors. Animal laboratories are assisting with testing human samples resulting in delays for diagnoses of animal samples, while routine veterinary, vaccination and surveillance programmes have been hampered by lockdowns and restrictions on movement.

FAO continues to work with WHO and OIE to monitor outbreaks, offer support to countries for detecting and reporting disease events, and provide training, tools and equipment to assess risks, prepare for and respond to outbreaks. While the COVID-19 pandemic has curbed some in-country trainings and working group activities, FAO has successfully adapted to virtual and hybrid facilitation.

Vaccination against avian influenza is one option, but it can never replace the impact of appropriate biosecurity measures which should be maintained at all times. Poultry vaccination can help reduce virus circulation and prevent the occurrence of major disease outbreaks or further spread, but it should only be implemented along with other controls.

Poultry vaccination is more complex than it seems and appropriate vaccination coverage needs to be achieved in order for it to be successful. Well-planned and regularly evaluated national vaccination strategies help avoid spending money for poor results. Moreover, badly implemented or incomplete vaccination may facilitate avian influenza spread. Given the rapid evolution of these viruses, vaccines need to be constantly updated to match currently circulating field strains.

Vaccination yielded very good results in China where a nationwide poultry vaccination was launched in September 2017 to tackle the H7N9 avian influenza virus that was circulating in poultry and sporadically spilled over to humans, especially in live bird market settings. Appropriate vaccination coverage in poultry significantly reduced the number of human cases in only a few weeks.

If countries consider vaccination as one potential tool in the fight against HPAI, FAO’s  Focus On: Rational use of vaccination for control and prevention of H5 HPAI and the Vaccination Planning Tool for Avian Influenza can be consulted.

While wild birds can facilitate long-distance avian influenza spread, local poultry trade remains the most important risk factor. Appropriate cleaning and disinfection is critical to prevent virus introduction, environmental persistence and spread, especially in contexts where birds from diverse backgrounds mix frequently, such as live bird markets. Biosecurity protocols should include a ban on overnight stays at markets and routine cleaning of premises. FAO strongly recommends support for biosecurity practices among backyard farmers, who account for the majority of poultry production. In addition, major festivals, especially if they involve surging demand for poultry, can also be a key driver for the spread of avian influenza.

If avian influenza is suspected in a country, it is appropriate to immediately restrict movements from the potentially affected areas to avoid further spreading the virus and, upon confirmation of the disease by the laboratory, to cull the affected flock, followed by cleaning and disinfection of the premises.

Setting up a dedicated telephone hotline and having good field reporting systems (like FAO’s Event Mobile Application, EMA-i) in place can be instrumental in identifying and addressing outbreaks early.

Market profiling can be conducted, for example using FAO’s Market Profiling Application, MPA, to select markets with high throughput and low biosecurity for targeted surveillance and risk mitigation measures. Depending on the context, vaccination of high risk or high value poultry flocks may be one of the options to consider, in combination with other measures.

Countries can access FAO technical support directly through FAO Emergency Centre for Transboundary Animal Diseases (ECTAD) country teams or Regional Animal Health Officers, or send requests to [email protected]. 

FAO has published detailed recommendations on how poultry sector stakeholders and animal health authorities can prevent, detect and respond to avian influenza introduction or spread:

• Biosecurity guide for live poultry markets
• Biosecurity for Highly Pathogenic Avian Influenza
• Preparing for Highly Pathogenic Avian Influenza
• Good Emergency Management Practice: The Essentials
• Focus On: Rational use of vaccination for control and prevention of H5 HPAI
• Vaccination Planning Tool for Avian Influenza

The current avian influenza epidemic has come at a time of economic stress and agri-food system challenges due to the COVID-19 pandemic.

Avian influenza can be a high burden for affected countries as outbreaks trigger significant economic losses for the poultry industry and rural livelihoods, as well as reducing available animal protein. Women and children are often in charge of small-scale poultry farming, which gives them an independent income. HPAI strains cause high poultry mortality rates and require large-scale culling.

Well-defined and fair compensation schemes play a significant role in incentivizing farmers to report disease suspicion, as otherwise farmers may opt for selling their affected animals at a lower price instead of losing everything. At the same time, culling and compensation policies can become very costly for a government when multiple outbreaks occur across a country. Regular poultry vaccination campaigns also imply high costs and complicated cold-chain logistics. Affected countries or those at risk are therefore advised to adopt an avian influenza preparedness and control plan and allocate sufficient budget to the planned activities. Poultry import bans implemented by unaffected countries result in market losses for the poultry industry of affected countries. Several million birds in Europe and Asia have been slaughtered due to the current and 2019/20 epidemics.