Avian Influenza

Unique identifier / Notation

BI0245

Synonyms

Bird Flu Avian Flu HPAI (en) influenza aviaire grippe aviaire (fr) influenza aviar gripe aviar (es) 禽流感 (cn)

Avian influenza is an infectious disease of birds caused by type A influenza viruses of the Orthomyxoviridae family. Naturally occurring among wild bird populations, avian influenza viruses can infect domestic poultry and other bird species. Some avian influenza viruses can also infect mammals and those affecting humans are called zoonotic. A pandemic can occur when a novel influenza virus spreads in human populations worldwide (adapted from FAO, 2009; WHO, 2023a; 2023b; WOAH, no date).

Primary reference(s)

FAO, 2009. Preparing for Highly Pathogenic Avian Influenza. Food and Agriculture Organization of the United Nations (FAO). Accessed 29 May 2025.

WHO, 2018. Influenza (Avian and other zoonotic). World Health Organization (WHO). Accessed 3 October 2020.

WHO, 2023a. Influenza (Avian and other zoonotic). World Health Organization. Accessed 29 May 2025.

WHO, 2023b. Managing epidemics: key facts about major deadly diseases, 2nd edition. WHO. Accessed 29 May 2025.

WOAH, no date. Avian Influenza. World Organisation for Animal Health (WOAH). Accessed 29 May 2025.

Annotations

Additional scientific description

Human

Avian influenza is transmitted by direct contact with infected birds or through contaminated environments (farms, markets, cages, vehicles, etc.) (WOAH, no date). Live poultry and poultry products trade and movements play an important role in national and cross-border spread. Certain avian influenza strains have also been shown to spread through migratory wild bird movements, sometimes over long distances (FAO, 2016, 2017). Biosecurity measures on farms and in live poultry markets are important to prevent disease introduction or spread (FAO, 2015).
Type A influenza viruses include many different subtypes, classified according to the nature of the two components that make up the virus - haemagglutinin (H) and neuraminidase (N) - proteins found on the surface of influenza viruses. There are 18 haemagglutinin and 11 neuraminidase subtypes of influenza A virus, giving rise to hundreds of variations on the 'HxNy' combination. Since the emergence of the H5N1 Highly Pathogenic Avian Influenza (HPAI) virus subtype in 1997 in Asia, several other subtypes have appeared due to the constant evolution and diversification of avian influenza viruses and progressively spread across continents (WOAH, 2016; CDC, 2017).
In 1997, human infections with A(H5N1) viruses were reported during an outbreak in poultry in Hong Kong SAR, China. Since 2003, this virus has spread in bird populations from Asia to Europe and Africa, and to the Americas in 2021, and has become endemic in poultry populations in many countries. Outbreaks have resulted in millions of poultry infections, several hundred human cases and many human deaths. Human cases have been reported mostly from countries in Asia, but also from countries in Africa, the Americas and Europe (WHO, 2023).
In 2013, human infections with A(H7N9) viruses were reported for the first time in China. The virus spread in the poultry population across the country and resulted in over 1500 reported human cases and many human deaths from 2013 to 2019. No further human cases have been reported to WHO since 2019. Since 2014, sporadic human infections with avian influenza A(H5N6) viruses have been reported almost exclusively from China. Other avian influenza viruses have resulted in sporadic human infections (WHO, 2023).

Animal

Avian influenza is preventable through control measures, including vaccination. As avian influenza viruses antigenically change over time, the use of appropriately matched vaccines is important (OFFLU, 2023). Each country has a policy in handling avian influenza, especially on vaccination. Countries permitting vaccination in poultry have a list of approved vaccines. Contact national veterinary services to learn what is allowed in the country before purchasing.

Highly pathogenic avian influenza (HPAI) causes variable clinical signs and high mortality rates in both wild and domestic bird populations. In certain bird species, some HPAI viruses do not necessarily produce significant clinical disease (WOAH, 2024a).
Avian influenza viruses can infect domestic poultry and other bird species; some avian influenza viruses can also infect mammals.
AIV has been shown to infect domestic mammals such as cats and cattle, as well as wild mammals including terrestrial (e.g. foxes, skunks, raccoons) and marine species (e.g., seals, sea lions) (FAO, no date).
Avian influenza is transmitted by direct contact with infected birds or through contaminated environments (farms, markets, cages, vehicles, etc.).
Live poultry and poultry products trade and movements play an important role in national and cross-border spread. Certain avian influenza viruses have also been shown to spread through migratory wild bird movements, sometimes over long distances. Biosecurity measures on farms and in live poultry markets are important to prevent disease introduction or spread (FAO, 2015).
Highly pathogenic avian influenza (HPAI) is one of the WOAH Listed diseases (WOAH, 2024b).
Avian influenza viruses of the H5 and H7 subtypes, as well as any influenza A virus with high pathogenicity are notifiable to the World Organization for Animal Health (WOAH) under the Terrestrial Animal Health Code.

Metrics and numeric limits

Strains are considered to be of high pathogenicity if they cause more than 75% mortality within 10 days, or inoculation of 10 susceptible 4- to 8-week-old chickens resulting in an intravenous pathogenicity index (IVPI) of greater than 1.2. (WOAH, 2024a).

Key relevant UN convention / multilateral treaty

United Nations, 2023. UN Model Regulations Rev. 23. United Nations. Available from: https://unece.org/transport/dangerous-goods/un-model-regulations-rev-23 Accessed 1 January 2025.

WHO. 2016. International Health Regulations (2005), 3rd ed. (WHO, 2016). Codex Alimentarius (FAO, no date).

WTO. 1998. The WTO Agreement on the Application of Sanitary and Phytosanitary Measures (SPS Agreement) (WTO, 1994). The WTO and the World Organization for Animal Health (OIE) G/SPS/GEN/775 (WTO, 1998).

Drivers

Human

For avian influenza viruses, the primary risk factor for human infection appears to be exposure to infected live or dead poultry or contaminated environments, such as live bird markets. Slaughtering, defeathering, handling carcasses of infected poultry, and preparing poultry for consumption, especially in household settings, are also likely to be risk factors. There is no evidence to suggest that A(H5), A(H7N9) or other avian influenza viruses can be transmitted to humans through properly prepared and cooked poultry or eggs. A few influenza A (H5N1) human cases have been linked to the consumption of dishes made with raw contaminated poultry blood.

Animal

Introduction of an avian influenza virus to a susceptible flock via poultry trade-related activities or farming and sale (live bird markets), or wild birds and migratory routes (WOAH, no date).

Impacts

Human

Exposure to avian influenza viruses can lead to infection and disease in humans, ranging from mild, flu-like symptoms or eye inflammation to severe, acute respiratory disease and/or death. Disease severity will depend upon the virus causing the infection and the characteristics of the infected individual. Rarely, gastrointestinal and neurological symptoms have been reported. The case fatality rate for A(H5) and A(H7N9) subtype virus infections among humans is higher than that of seasonal influenza infections (WHO, 2023). An influenza pandemic will occur when an influenza virus emerges with the ability to cause sustained human-to-human transmission, and the human population has little to no immunity against the virus. With the growth of global travel, a pandemic can spread rapidly. Whether currently circulating avian, swine and other influenza viruses will result in a future pandemic is unknown. However, the diversity of zoonotic influenza viruses that have caused human infections necessitates strengthened surveillance in both animal and human populations, thorough investigation of every zoonotic infection and pandemic preparedness planning. Influenza viruses are impossible to eradicate, and zoonotic infections will continue to occur.

Since 1997 several studies have contributed to fundamental insights into the pathology and pathogenesis of human H5N1 influenza. Aside from the respiratory tract, other organs such as the intestines, the brain, and the placenta appear to be infection targets of the virus. The H5N1 virus is also capable of transplacental transmission to the foetus. Dysfunction of the immune system may be a key pathogenetic mechanism. At the molecular level, several viral genes and mutations in gene products have been suggested to be involved in increased virulence of H5N1 viruses. At the same time, however, it becomes increasingly apparent that what is known today about the virus and its pathogenicity is only the tip of the iceberg and that there are likely several additional pathogenetic mechanisms and molecular determinants of pathogenicity in H5N1 influenza yet to be identified (Korteweg et al., 2008).

Animal

Animal influenza outbreaks have the potential to be significant to public health and can have social and economic impacts (WHO, 2024d). Losses of rare and important wild bird species, as well as significant social and economic costs, including livelihood losses and egg shortages (FAO, no date). High mortality in poultry with sudden death of birds, may cause severe illness in humans, stamping-out of birds in the affected flock or farm, poultry movement restrictions, trade ban, livelihoods, food security and health implications, in particular women and children who often are the ones caring for poultry (WOAH, no date).

Multi-hazard context

While recently identified avian influenza viruses do not currently transmit easily from person to person, the ongoing circulation of these viruses in poultry is particularly concerning, as these viruses cause severe disease in humans and have the potential to mutate to become more contagious between people (WHO, no date a).

Risk Management

Human

To minimize public health risks, quality surveillance in both animal and human populations, thorough investigation of every human infection and risk-based pandemic planning areessential. Public healthand animal health authorities should work together and share information during investigations of human cases of zoonotic influenza (WHO, 2023).

The public should minimize contact with animals in areas known to be affected by animal influenza viruses, including farms and settings where live animals may be sold or slaughtered, and avoid contact with any surfaces that appear to be contaminated with animal faeces. Children, older people, pregnant and postpartum women (up to 6 weeks) or people with suppressed immune systems should neither collect eggs nor assistwith slaughtering or food preparation. Travellers to countries and people livingin countries with known outbreaks of avian influenza should, if possible, avoid poultry farms, contact with animals in live poultry markets, entering areas where poultry may be slaughtered, and contact with any surfaces that appear to be contaminated with faeces from poultry or other animals. Travellers returning from affected regions should report to local health services if respiratory symptoms suspecting zoonotic influenza virus infection (WHO, 2023).

influenza by continuously functioning as a global mechanism of surveillance, preparedness and response for seasonal, pandemic and zoonotic influenza; globalplatform for monitoring influenza epidemiology and disease; and global alertfor novel influenza viruses and other respiratory pathogens (WHO, 2024; WHO, no date c).

Twice a year, WHO consults with experts from WHO Collaborating Centres, Essential Regulatory Laboratories and other partners to review data generated by GISRS and animal health partners on influenza viruses with pandemic potential and assesses the need for additional candidate vaccine viruses for pandemic preparedness purposes. Based on risk assessment, WHO provides guidance, develops and adjusts surveillance, preparedness and response strategies to seasonal, zoonotic and pandemic influenza, and communicates timelyrisk assessment outcomes and intervention recommendations with Member Statesto enhance preparedness and response nationally and globally. The WHO Pandemic Influenza Preparedness Framework implements a global approach to prepare for the next influenza pandemic (WHO, 2023).

Animal

Farm and market biosecurity improvement, movement control, depopulation, tracing back/forward, vaccination (prevention, onlyif the country allows vaccination of birds against avian influenza), compartmentalization, food hygiene (WOAH, no date).

Monitoring

The table below offers an overview of monitoring for harmful algal blooms. This information can be used for forecasting within a national early warning system (EWS). Since EWS capacities and processes differ across countries, the most current and specific information regarding EWS should be obtained from the appropriate national or regional agency/authority responsible for disaster management.

Which institution(s) produce(s) Disaster Risk Data/Information?

WHO, Ministry of Health, FAO Reference Centres, WOAH Reference Centres

How is the Hazard Observed/Monitored/Forecast?

FAO empres-i+ https://empres-i.apps.fao.org/diseases

WOAH WAHIS https://wahis.woah.org/#/event-management

Through its Global Influenza Surveillance and Response System (GISRS). WHO, in collaboration with the World Organisation for Animal Health (WOAH) and the Food and Agriculture Organization of the United Nations (FAO), conducts surveillance at the human-animal interface, assesses the associated risks and coordinates response to zoonotic influenza outbreaks and other threats to public health (WHO, 2023).

WHO supports countries to conduct all-hazards strategic risk assessment in the contexts of health emergencies and disasters, which results in the development of a country's risk profile. Empowered with the country risk profile, inclusive of a seasonal risk calendar, countries can anticipate potential emergencies before they occur to trigger early alerts and inform early actions (WHO, 2021).

WHO's Early Warning, Alert and Response System (EWARS) has been designed to improve disease outbreak detection in emergency settings, such as in countries in conflict or following a natural disaster. It is a simple and cost-effective way to rapidly set up a disease surveillance system. EWARS is deployed during an emergency as an adjunct to the national disease surveillance system. WHO works with Ministries of Health and health sector partners to train local health workers to use the system. After the emergency, EWARSs should re-integrate back into the national system (WHO, no date a).

Human

To minimize public health risks, quality surveillance in both animal and human populations, thorough investigation of every human infection and risk-based pandemic planning are essential. Public health and animal health authorities should work together and share information during investigations of human cases of zoonotic influenza (WHO, 2023).

The public should minimize contact with animals in areas known to be affected by animal influenza viruses, including farms and settings where live animals may be sold or slaughtered, and avoid contact with any surfaces that appear to be contaminated with animal faeces. Children, older people, pregnant and postpartum women (up to 6 weeks) or people with suppressed immune systems should neither collect eggs nor assist with slaughtering or food preparation. Travellers to countries and people living in countries with known outbreaks of avian influenza should, if possible, avoid poultry farms, contact with animals in live poultry markets, entering areas where poultry may be slaughtered, and contact with any surfaces that appear to be contaminated with faeces from poultry or other animals. Travellers returning from affected regions should report to local health services if respiratory symptoms suspecting zoonotic influenza virus infection (WHO, 2023).

Global influenza surveillance has been conducted through WHO's Global Influenza Surveillance and Response System (GISRS) since 1952. GISRS currently comprises institutions in 129 WHO Member States. The mission of GISRS is to protect people from the threat of influenza by continuously functioning as a global mechanism of surveillance, preparedness and response for seasonal, pandemic and zoonotic influenza; global platform for monitoring influenza epidemiology and disease; and global alert for novel influenza viruses and other respiratory pathogens (WHO, 2024; WHO, no date b).

Twice a year, WHO consults with experts from WHO Collaborating Centres, Essential Regulatory Laboratories and other partners to review data generated by GISRS and animal health partners on influenza viruses with pandemic potential and assesses the need for additional candidate vaccine viruses for pandemic preparedness purposes. Based on risk assessment, WHO provides guidance, develops and adjusts surveillance, preparedness and response strategies to seasonal, zoonotic and pandemic influenza, and communicates timely risk assessment outcomes and intervention recommendations with Member States to enhance preparedness and response nationally and globally. The WHO Pandemic Influenza Preparedness Framework implements a global approach to prepare for the next influenza pandemic (WHO, 2023).

Animal

Farm and market biosecurity improvement, movement control, depopulation, tracing back/forward, vaccination (prevention, only if the country allows vaccination of birds against avian influenza), compartmentalisation, food hygiene (WOAH, no date).