Policy paper

Avian influenza (bird flu): infection in wild birds and wild mammals

Updated 19 October 2023

Applies to England, Scotland and Wales

Wild birds are the natural hosts of avian influenza (bird flu) viruses. However, avian influenza viruses can also infect mammals.

How the viruses spread in wild birds

Wild birds can become infected through:

• direct contact with other infected birds and their secretions
• contact with contaminated feathers and faeces
• contact with contaminated objects, surfaces or environments (such as ponds, nest sites or feeding areas)
• eating infected birds or mammals

Wild birds can be infected within Great Britain (England, Scotland and Wales) or in another country and bring the virus to Great Britain when they migrate.

The signs of bird flu can vary depending on:

• if the bird is infected with a highly pathogenic avian influenza (HPAI) or a low pathogenic avian influenza (LPAI) virus
• the species of bird – some species (such as some ducks and geese) may show minimal clinical signs

How the viruses spread in mammals

The main risks of avian influenza viruses to mammals come from:

• having close contact with secretions of infected birds
• eating infected birds or raw meat from infected birds

A sick or dead wild bird can contain a significant amount of virus. Scavenging mammals that are opportunistic might eat infectious dead or sick birds and be exposed to very large quantities of virus. This gives the potential for the virus to enter a host population that it does not normally infect.

Surveillance in wild birds

The Animal and Plant Health Agency (APHA) carries out year-round surveillance for HPAI in dead wild birds in Great Britain. This is part of APHA’s wild bird surveillance programme.

The wild birds are collected following reports from the public and warden patrols. All dead birds in Great Britain can be reported.

APHA triages reports and does not collect all birds. They adjust the collection thresholds for dead wild birds for different species to increase or decrease the sensitivity of surveillance.

Results from wild bird testing help APHA understand the distribution of disease across the country and current risk to poultry and other captive birds.

Findings in wild birds

APHA publishes:

• an interactive map of reported wild bird mortality and findings of avian influenza virus in wild birds in Great Britain
• interactive dashboard of findings of avian influenza virus in wild birds in Great Britain
• weekly reports of HPAI findings in wild birds in Great Britain
• the current national risk level for HPAI in wild birds
• risk and outbreak assessments

Reported finding of HPAI in wild birds will underestimate the number of wild birds affected with bird flu. This is because the surveillance scheme only tests dead wild birds, and not all infected dead wild birds are reported or collected.

Surveillance in wild mammals

APHA monitors avian influenza viruses in wild mammals through routine testing of:

• land mammals found dead, including those investigated by the Diseases of Wildlife Scheme (DoWS)
• marine mammals found dead, including those reported to the Cetacean Strandings Investigation Programme

The APHA avian influenza National Reference Laboratory tests wild mammals that meet the case definition for avian influenza viruses. Read the influenza A (H5N1) infection in mammals: suspect case definition and diagnostic testing criteria.

Findings in mammals

APHA publishes:

• an interactive map of findings of avian influenza virus in wild mammals in Great Britain
• reports of findings of avian influenza virus in wild mammals in Great Britain 
• reports of confirmed cases of avian influenza virus infection in captive mammals in Great Britain

Avian influenza viruses may not have been the sole cause of death in these mammals. Other factors may have contributed.

Findings of avian influenza viruses in mammals are uncommon. Evidence of mammal-to-mammal transmission in the wild remains very limited. There is no evidence to suggest an increased risk to non-avian wildlife.

The Human Animal Infections Risk Surveillance (HAIRS) group, a cross-government horizon scanning and risk assessment group, assessed the risk of influenza A (H5N1) in non-avian wildlife to humans. They concluded that the risk is very low for the general population, and low for those exposed to infected non-avian wildlife species.

Protecting wild birds

The Department for Environment, Food and Rural Affairs (Defra) has set out a mitigation strategy for avian influenza in wild birds in England and Wales.

This explains how land managers, the public, ornithological and environmental organisations, and the government and its delivery partners can:

• reduce the impact of bird flu on wild bird populations
• protect public health, the wider environment and the rural economy

It includes a set of bird flu posters for landowners, local authorities and other organisations. They can display these posters on sites where there is a risk of bird flu or it has been detected in wild birds in the area.

The strategy also contains information on wild bird monitoring, including how:

• Defra supports wild bird population monitoring programmes
• the Avian Influenza Wild Bird Recovery Advisory Group uses monitoring information to guide their conservation and monitoring activities to protect wild birds

Monitoring wild bird populations is crucial to understanding the impact of bird flu on wild birds. As part of this work, the British Trust for Ornithology (BTO) issues bird ringing permits on behalf of Defra and Natural England. These allow permit holders to catch birds for ringing purposes, under the Wildlife and Countryside Act 1981.

The BTO HPAI Ringing Framework and information for volunteer field workers set out guidance for bird welfare and biosecurity when ringing birds.