Avian influenza (bird flu)

30 May 2022


Understand more about avian influenza and the possible implications of an outbreak

ALERT: Avian influenza: housing measures to be lifted
25 April 2022

The housing restrictions for poultry and captive birds, which were introduced in November to help stop the spread of bird flu, are to be lifted on 2 May. More >

This guidance is for England

Avian influenza is a highly infectious viral disease affecting the respiratory, digestive and/or nervous system of birds.

The severity depends upon the strain of the virus and the type of bird infected. Some strains - known as 'highly pathogenic avian influenza' - can cause severe disease in poultry, with a high death rate. The disease can develop so rapidly that birds may die without showing any previous signs of disease.

Other strains - known as 'low pathogenic avian influenza' - usually result in milder, less significant disease. However, certain low pathogen strains can mutate into highly pathogenic strains.

Possible impact of the disease

Highly pathogenic avian influenza can cause severe disease in susceptible birds. Low pathogenic avian influenza generally causes mild disease or no disease at all.

All bird species are thought to be susceptible to avian influenza. Migratory birds such as wild ducks and geese can carry the viruses, often without symptoms of illness, and show the greatest resistance to infection. However, domestic poultry flocks are particularly vulnerable to epidemics of a rapid, severe and fatal form of the disease.

Legislation and processes for management of the disease are different, depending on the circumstances of the outbreak - for example, whether highly pathogenic avian influenza is confirmed in poultry, other captive birds or wild birds, and whether the disease occurs at a farm, slaughterhouse or border inspection post.

The highly pathogenic H5N1 strain has shown the ability to jump the species barrier occasionally and cause severe disease in humans. It has not shown the ability to move easily between humans, but this is a cause for concern (see below).

Clinical signs

The severity depends upon the strain of virus and the type of bird infected. Birds infected with highly pathogenic avian influenza may die suddenly or show a range of clinical signs.

Individual birds with highly pathogenic avian influenza may show the following symptoms:

  • nervous signs (tremors and incoordination)
  • depression, sneezing and coughing
  • swollen, congested and oedematous wattles
  • haemorrhages on the hock (lower part of leg)
  • diarrhoea 

In the flock symptoms can be:

  • unusual quietness, decreased activity levels
  • decreased levels of vocalisation
  • decreased levels of feed and water consumption
  • decreased egg production

It is important to note that when infection is due to a highly pathogenic form of avian influenza, the onset of clinical signs is sudden, severe, short lasting and mortality is extremely high (sometimes 100%).

Avian influenza is a notifiable disease. If you suspect any type of bird flu you must tell the Animal and Plant Health Agency (APHA) immediately by telephoning 03000 200301. Failure to do so is an offence.

Procedures when disease is confirmed

The premises where disease is confirmed will be put under restriction so poultry or other captive birds cannot move on or off. It will be referred to as the infected premises. An approved disinfectant must be used to disinfect footwear, clothing and vehicles before entering or leaving the premises.

A protection zone of 3 km and a surveillance zone of 10 km are put in place around the infected premises where the disease has been confirmed. There are certain restrictions for keepers of poultry that are within the protection and surveillance zones. If avian influenza is confirmed it will be controlled in line with the contingency plan for exotic notifiable diseases and the notifiable avian disease control strategy will be implemented.


Biosecurity measures should be practised routinely. Avian influenza is spread through bird-to-bird contact and indirectly through contaminated feed, water, equipment, etc.

The boots, clothing and hands of any person who has been in contact with infected animals can spread the disease.

The Department for Environment, Food and Rural Affairs (Defra) and the Scottish and Welsh Governments have jointly published information on biosecurity and the measures you can take to protect your birds from disease, specifically avian influenza. It includes a poster on protecting your birds from avian influenza and a guidance document entitled Biosecurity and Preventing Welfare Impacts in Poultry and Captive Birds: Advice for all Captive Bird and Poultry Keepers (Including Game Birds, Waterfowl, and Pet Birds).

Legislation applicable to avian influenza

The Animal Health Act 1981 provides powers for the control of outbreaks of avian influenza. It was amended in 2002 to provide more powers to deal with foot-and-mouth disease and these powers were extended by the Avian Influenza and Newcastle Disease (England and Wales) Order 2003, so that they are now exercisable in relation to avian influenza (and Newcastle disease).

The Act provides for the slaughter of diseased poultry, poultry suspected of disease, poultry exposed to disease and poultry that the Secretary of State thinks should be slaughtered to prevent the spread of disease (a 'firebreak' cull).

The Diseases of Poultry (England) Order 2003 introduced a number of key amendments to the Animal Health Act 1981. The definition of poultry within section 87(4) of the Animal Health Act 1981 was amended to include all birds (including those in captivity) and the definition of disease in section 88(3) was extended to include all diseases of birds.

The Avian Influenza and Influenza of Avian Origin in Mammals (England) (No 2) Order 2006 allows for a flexible and risk-based approach to disease control, which will enable industry to continue to operate in a safe and biosecure manner.

The Order contains preventive measures such as:

  • power for the Secretary of State to declare an avian influenza prevention zone
  • ban or limitation of bird gatherings
  • separation of birds from wild birds
  • surveillance for avian influenza

The Order includes a range of provisions for application in cases of suspected and confirmed avian influenza, both highly pathogenic and low pathogenic.

The Avian Influenza (H5N1 in Wild Birds) (England) Order 2006 provides controls in the event that avian influenza H5N1 is found in wild birds. Under the Order, the Secretary of State can declare a wild bird control area and a wild bird monitoring area and ensure the inspection of commercial premises in such areas.

The Avian Influenza (Vaccination) (England) Regulations 2006 prohibit vaccination but allow the Secretary of State to declare an emergency vaccination zone or a preventive vaccination zone. The Secretary of State can also serve an emergency vaccination notice on individual premises. Within the zones or on individual premises the Secretary of State can require the vaccination of poultry and other captive birds. Movement restrictions will apply within the zones.

The Avian Influenza (Preventive Measures) (England) Regulations 2006 ban fairs, markets, shows or other gatherings of poultry or birds. In practical terms bird gatherings have been permitted to take place under a general licence, but the organiser must notify APHA on 03000 200301 or [email protected]. The position in relation to bird gatherings remains under continual review, in consideration of the wider risk. There is an ongoing requirement in the Regulations for keepers of poultry flocks of 50 or more birds to register.

They also restrict the vaccination of birds in zoos. The Secretary of State can require vaccination of birds in zoos to be carried out. Certain measures apply to vaccinated birds in zoos and the Secretary of State can require surveillance at these zoos.

The Avian Influenza and Newcastle Disease (Contingency Planning) (England) Order 2003 provides for the preparation of a national contingency plan indicating the arrangements to be put in place for the control and eradication of avian influenza (and Newcastle disease). The national contingency plans for these diseases must be issued on an annual basis for public consultation and issued to Parliament.

Effect on food and humans

Advice from the World Health Organisation (WHO) is that there is no health risk from well cooked poultry meat or from eggs. For further information please see the WHO website.

Avian influenza is primarily a disease of birds. Humans can only be infected with the disease through close contact with live infected birds.

Transmission of avian influenza viruses to people remains relatively rare and in most cases occurs as a result of direct contact with infected poultry or other birds or their faeces. At present the virus cannot transfer directly from human to human.

There is concern that the virus may change (or mutate) to emerge as a new virus that is transmissible between people and capable of causing disease in people, birds and other animals.

Public health control measures in any outbreak of avian influenza amongst poultry will therefore aim to protect people against avian influenza and also protect against the risk of any mutation of the virus.

For more information please see the section of the GOV.UK website on avian influenza: guidance, data and analysis.


Livestock keepers can stay up to date with the latest avian influenza developments via the APHA alert subscription service.

Trading standards

For more information on the work of trading standards services - and the possible consequences of not abiding by the law - please see 'Trading standards: powers, enforcement and penalties'.

In this update

No major changes.

Last reviewed / updated: April 2022

Key legislation

Please note

This information is intended for guidance; only the courts can give an authoritative interpretation of the law.

The guide's 'Key legislation' links may only show the original version of the legislation, although some amending legislation is linked to separately where it is directly related to the content of a guide. Information on amendments to legislation can be found on each link's 'More Resources' tab.

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