Avian influenza (AI) is a notifiable disease in the UK, and one that often pops up in the news cycle. But many veterinary staff members are often unaware of the implications of AI in clinical practice, and how much of a role general practice vets also play in preventing the spread of this disease throughout the UK.
Classifying avian influenza
Influenza viruses viruses come from the family Orthomyxoviridae and are divided into four known types: A, B, C and D. AI viruses are type A viruses, and are further classified based on the antigenic proteins haemagglutinin (H) and neuraminidase (N) present on the viral capsid (Styles, 2016). These H and N proteins are then used to categorise the virus based on the proteins present. There are 16 different H subtypes and nine different N subtypes (Styles, 2016). Further classification of the virus is based on the pathogenic potential – high pathogenic avian influenza (HPAI) and low pathogenic avian influenza (LPAI). The H and N protein subtype designation gives a clue as to the pathogenicity of the virus – all known HPAI contains either H5 or H7 haemagglutinin proteins; however, not all H5 or H7 designations are HPAI viruses (Styles and Nadler, 2019).
An antigenic shift occurs when a host is co-infected with two subtypes of AI that undergo recombination and can create a new virus, which can rapidly increase the virulence of the virus, or the way it interacts with the host’s immune system
All known influenza A subtypes have been identified in birds, with waterfowl and shore birds considered to be natural reservoir hosts for AI viruses (Zambon, 1999). This means that wild birds act as asymptomatic carriers of AI. Type A influenza viruses mutate by antigenic shift and antigenic drift, both of which occur in the host. Antigenic drift refers to small changes in the genetic code of the virus, which does not alter the virus significantly (Taubenberger and Kash, 2010). However, antigenic shift occurs when a host is co-infected with two subtypes of AI that undergo recombination and can create a new virus, which can rapidly increase the virulence of the virus, or the way it interacts with the host’s immune system (Styles, 2016).
Prevalence and clinical signs of avian influenza
Identifying a bird that is possibly carrying AI is difficult, as the symptoms can be non-specific or mirror other possible respiratory or neurological illnesses; information on possible clinical signs can be found here (Figure 1).
As these symptoms are non-specific and can encompass many different disease pathologies, a joint statement by the British Veterinary Association (BVA), British Veterinary Zoological Society (BVZS), The British Veterinary Poultry Association (BVPA) and the British Small Animal Veterinary Association (BSAVA) has indicated when a veterinarian should raise suspicions. If any bird in joint housing shows signs of unresponsiveness or huddling, or if there is a sudden and rapid increase in unexpected deaths, concerns should be raised. If there are any birds with severe disease, clinical signs including neurological signs such as shaking and twitching, twisted heads or necks, swollen heads, blue discoloration of the non-feathered areas of the head, weakness, bruising or dyspnoea, then concerns should also be raised for the possibility of AI (BVA, BVZS, BVPA and BSAVA, 2024). As AI is a notifiable disease, any suspicion should be reported to Defra without delay.
AI is endemic in wild birds across the world, and the same is true for the UK. During most of the year, LPAI remains endemic in wild waterfowl and shore birds and causes minimal risk. However, the appearance of migrating birds through the winter mixing with wild birds in Europe and travelling to the UK brings new subtypes of AI that can undergo antigenic shift, resulting in HPAI. This is why AI is often an issue through winter when the temperatures are colder, and wild migrating birds are flocking.
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Prevention of disease spread
All owners of poultry or captive birds must register their birds with the Animal and Plant Health Agency (APHA), and it is against the law for bird owners not to comply with this. Different forms exist for owners of fewer than 50 birds and 50 or more birds, and for owners of birds of prey. Being registered means that bird owners can keep up to date with changes in biosecurity rules and Avian Influenza Prevention Zone (AIPZ) rules in their area and be warned about HPAI outbreaks nearby.
It is also recommended to prevent contact between captive birds and wild birds. This can be facilitated by using bird deterrents, spike strips and foils or streamers, and by netting any ponds or bodies of water to prevent waterfowl from contaminating these with faeces. Food, bedding and water should be stored in a covered area, and outside areas should be cleaned daily to remove any wild bird faeces, feathers or carcasses.
At the time of writing, the UK has already experienced its first cases of HPAI for this winter, and an AIPZ mandating enhanced biosecurity has been put in place over the entirety of England, Scotland and Wales. At present, this means that bird keepers must follow strict increased biosecurity measures to prevent spread of HPAI, but mandatory housing measures are not in place for the whole country. However, in areas that have already had several cases of HPAI, an AIPZ mandating both enhanced biosecurity and mandatory housing measures has come into effect in areas of East Riding of Yorkshire, North Yorkshire, Kingston upon Hull, Lincolnshire, Norfolk, Suffolk, Shropshire, York, Cheshire, Herefordshire, Lancashire, Merseyside and Worcestershire (Defra and APHA, 2025a).
As is usual for such a situation, the AIPZ rules and zones are changing constantly, and the most up-to-date information can be found on government websites. A country-wide interactive map (Figure 2) is available that identifies areas where outbreaks have occurred, where the control, protection and surveillance zones are, and which parts of the country are covered by the different AIPZ zones.
Biosecurity measures
Biosecurity measures inside an AIPZ, which currently encompasses all of England, Scotland and Wales, include the following requirements for bird keepers (Defra and APHA, 2024; Defra and Hickman, 2025).
- Cleanse and disinfect clothing, footwear, equipment and vehicles before and after contact with poultry and captive birds – if practical, use disposable protective clothing
- Reduce the movement of people, vehicles or equipment to and from areas where poultry and captive birds are kept, to minimise contamination from manure, slurry and other products
- Carry out effective vermin control in any areas where poultry and captive birds are kept
- Thoroughly cleanse and disinfect housing on a continuous basis
- Keep fresh disinfectant at the right concentration at all farm and poultry housing entry and exit points
- Minimise direct and indirect contact between poultry and captive birds and wild birds, including making sure all feed and water is not accessible to wild birds
- Prevent access by poultry to ponds and watercourses and ensure that birds are kept in fenced or enclosed areas
- Keep records of bird and egg movements and records of bird deaths and disposal, and make these available to an inspector on demand
- Do not keep waterfowl in the same enclosures as other birds, with the exception of those in zoos
- Contain any wild game caught up during open season for 21 days prior to moving
- Maintain all buildings that house birds to prevent leakage of water or contamination from wild birds
Any disinfectant used must be Defra approved and mixed to the correct concentration as specified by the list of approved disinfectants for use in England, Scotland and Wales. This information has been provided by Defra and is available for access here.
If captive birds are present within an AIPZ that includes mandatory housing measures, bird owners will have to follow the above biosecurity measures as well as the mandatory housing measures. The mandatory housing measures mean that these birds must be housed indoors, in secure buildings that prevent the entry of wild birds. All openings in these buildings must be covered with mesh or netting, with a maximum hole size of 25x25mm. Any birds that are not able to be kept inside on welfare grounds must only be allowed access to outdoor areas that are netted with a minimum net hole size of 25x25mm, and have no access to permanent standing water sources. More detail on these requirements can be found here.
When a case of HPAI is suspected, a 3km and 10km temporary control zone are put into place to prevent disease spread. If HPAI is confirmed in these zones, they become either a 3km protection zone and 10km surveillance zone, or a 3km captive bird monitoring controlled zone. When a bird is within a protection or a control zone, this means that poultry, poultry meat and eggs cannot be moved into or out of the premises without a licence. In addition, disposal of carcasses must be performed following instructions given by a veterinary inspector, and poultry litter must not be spread or removed from the premesis. If the birds are outside of the 3km zone but within the 10km surveillance zone, all egg movements must be recorded, and all poultry, captive birds and other mammals, as wells as any poultry litter must not leave the premises. It is important to note that exceptions can be made for pet birds in these situations, but must be approved by APHA (Defra and APHA, 2025b).
The role of the general practitioner
Veterinary staff do not currently have an obligation to report owners who are not following the mandatory guidelines for their area, but should be able to provide sound and accurate advice for pet owners who may have questions. As such, it is important to keep up to date with the AIPZ requirements for the area in which you practise, in order to give advice about movement or transport of birds. The main sources for spread of AI to captive birds include direct contact with wild birds, especially waterfowl and gulls, direct contact with faeces from affected birds, and contaminated footwear, clothing, vehicles and equipment (Defra and APHA, 2024).
A 20-year-old parrot who has lived inside for their lifetime that presents with respiratory symptoms is highly unlikely to be a carrier for AI, compared to a backyard duck who is allowed to free range over a large garden and interact directly with wild birds
It is also very important not to compromise animal welfare because of lack of knowledge or inexperience. Many veterinary practices will have their own AI protocols which need to be followed, especially for birds who live outside. However, a 20-year-old parrot who has lived inside for their lifetime that presents with respiratory symptoms is highly unlikely to be a carrier for AI, compared to a backyard duck who is allowed to free range over a large garden and interact directly with wild birds.
In many cases, birds can be assessed and treated outside in the car park while wearing appropriate personal protective equipment, for example with backyard chickens or birds of prey (Figure 3). In most, if not all, cases where the bird has lived indoors for a significant amount of time and has not been in contact with wild birds, there should be no risk factors that preclude them being brought into the clinic to receive appropriate care (Figure 4). If in doubt, a risk analysis can be performed with direct visual inspection prior to inviting the bird into the clinic. Veterinarians, veterinary nurses and veterinary receptionists must be aware that implying that the only help that can be provided for a much-loved pet bird is euthanasia will make a distressing situation for the owner even more stressful.
Final thoughts
It is important for veterinary staff to keep up to date with the changes in the situation and advise clients who own birds accordingly
AI in the UK is an ever-changing situation that should be monitored closely, especially for practices who register birds and are within AI prevention zones, or surveillance zones following outbreaks of HPAI. It is important for veterinary staff to keep up to date with the changes in the situation and advise clients who own birds accordingly. AI in captive pet birds is very uncommon, and other differential diagnoses should be considered in individuals that are low risk.
