As we’re a few months into this year’s AI season, vet Matt Balfour highlights some key areas to focus on that can help reduce its spread in poultry sites.
In the current 2025-26 period (starting 1 October 2025) there’s been, at the time of writing, 92 cases of AI in poultry units, plus significant numbers of wild bird detections across a range of species. This poses a huge challenge to the poultry sector, with the value of birds alone lost during the devastating 2022-23 outbreak calculated at £52 million.
Added to this are costs of business disruption, cleaning and disinfection, compliance with control zone restrictions and international trade losses, and the serious bird welfare impacts on infected premises. The transmission of HPAI, therefore, must be fully understood to implement practical biosecurity measures to limit its spread into or within poultry units.
The role of wild birds
Wild birds can carry and shed virus, serving as reservoirs and sentinels. Although all wild bird species are susceptible to infection, of particular concern are these bird orders:
Anseriformes: e.g., duck, geese, swans
Charadriiformes: e.g., gulls, auks, terns
These orders account for the majority of wild bird detections and pose the most significant risk to poultry units. However, the virus has been detected in a broad range of other species, such as puffins, red kite, partridge and wood pigeon.
Wild birds in the UK may become infected either locally: if the virus is already circulating or present in the environment, or abroad: from infection during seasonal migration.
Outbreaks can occur year-round but risk increases seasonally, particularly in late autumn and early winter, when migratory waterbirds arrive via two main flyways.:
- The Black Sea-Mediterranean route (linking Europe, Africa, and the Middle East)
- The East Atlantic flyway (connecting Scandinavia, northern Europe, Greenland, and North America to the UK)
These flyways overlap, and species mix extensively, often with viral reassortment and the emergence of novel variants. When the virus reaches our shores, infections can spread among both migratory and resident wild birds.
Transmission into, or within, poultry units
Introduction into poultry units depends on:
- Infection levels within the local wild bird population
- The susceptibility of the poultry species involved
- Biosecurity standards within the poultry unit
HPAI spreads through direct contact between birds via respiratory secretions and faeces, and indirectly through contaminated environments such as water, soil, equipment, and housing. There is also evidence for limited airborne transmission of the virus. For these reasons, it is vital to ensure anything or anyone entering the bird area is free from disease. Here are some practical measures which I believe are particularly important:
- Ensure all staff and visitors are correctly using the double stepover barrier. This is a far more effective means of disease control than foot dips by themselves (which tend to become contaminated, or to not properly disinfect soiled footwear)
- If using non-mains water source, which is at risk of contamination, ensure the water is being treated constantly with a water sanitiser (e.g., chlorine dioxide, hydrogen peroxide)
- Fix leaking roofs, vents or walls urgently. A significant number of HPAI outbreaks have been started by contaminated water entering the shed
- Use enrichment and bedding which has been stored in a rodent/wild birds proof area and has outer packaging which can be disinfected before it’s placed into the bird area
- Make sure all vents are fully meshed with 25x25mm (or smaller) meshing. This is sufficient to prevent access to even small wild birds to the bird area
- Ensure excellent rodent control. Both rats and mice are excellent vectors for disease and have been implicated in HPAI outbreaks
- When discussing the infection risk to a poultry unit, susceptibility of the poultry species or breed type housed should be considered. Susceptibility cannot be directly correlated with the number of reported cases per species or breed type (as a proportion of total units), due to differences in housing and management practices
Virus survivability
The HPAI survives for markedly different periods, depending on environmental conditions. For example, HPAI tolerates cold or even freezing (to as low as -20°C) conditions well, and H5N1 virus has been shown to be able to survive for 240 in feather tissue, 160 days in muscle and 20 days in liver at 4°C. At warmer temperatures for 20-22°C, virus survivability drops to 6 days in infected carcases. As a rule of thumb, the virus survives well in cold, damp environments but is rapidly inactivated by heat, drying, and ultraviolet light, contributing to its marked autumn-winter seasonality in the UK.
Unfortunately, HPAI is unlikely to disappear soon, so we must continue to adapt. While we cannot control migratory flyways or wild bird infection levels, we can control what happens on farm. Meticulous, consistent biosecurity remains our strongest defence, and this is best done by understanding the key features of the virus and taking an evidence-based approach. By regularly reviewing risk points and acting swiftly to address weaknesses, there’s a reduced likelihood of virus introduction and we can help protect both bird welfare and business resilience.
If you have any concerns about your birds, get in touch with us by calling 01392 872932