Avian influenza remains a major industry challenge. Not only is there a significant financial impact, but the emotional toll on those sites affected shouldn’t be underestimated.
Understanding Highly Pathogenic Avian Influenza (HPAI) transmission is essential to implementing effective biosecurity measures to prevent its spread within and between poultry units.
Wild birds
Wild birds carry and shed the virus. Of particular concern are Anseriformes (ducks, geese and swans) and Charadriiformes (gulls, auks and terns), although all wild bird species are susceptible.
Wild birds may be infected in the UK through local virus circulation or abroad during seasonal migration. While outbreaks can occur year-round, risk rises in late autumn and early winter as migratory waterbirds arrive via the Black Sea-Mediterranean and East Atlantic flyways.
These overlapping flyways bring species into close contact, enabling viral reassortment and new variants to emerge. Once in the UK, the virus can spread among migratory and resident wild birds.
Transmission
HPAI introduction into poultry units depends on local wild bird infection levels, poultry species susceptibility and biosecurity standards.
HPAI spreads through contact between birds via respiratory secretions, faeces and contaminated environments like water, soil, equipment and housing. Limited airborne transmission is also possible, meaning anyone or anything entering bird areas must be disease-free.
When assessing infection risk, consider the poultry species or breed housed. Reported cases alone cannot indicate susceptibility, as housing and management practices vary. However, UK cases suggest turkeys, ducks and broiler breeders are disproportionately affected, while broilers are under-represented. Studies show some H5N1 strains can infect turkeys at doses over 100 times lower than those needed for chickens.
Virus survivability
HPAI survives longest in cold, damp conditions, even at -20°C. At 4°C, H5N1 can persist for 240 days in feathers, 160 days in muscle and 20 days in liver. At 20–22°C, survival in infected carcases drops to six days. Heat, drying and UV light rapidly inactivate the virus, contributing to its autumn-winter seasonality in the UK.
Ongoing vigilance is essential. While we cannot control wild bird movements or infection levels, consistent biosecurity and regular risk assessments can reduce virus introduction, protect bird welfare and strengthen your business resilience.
If you have any concerns about your birds or would like to talk about your biosecurity, get in touch with our vets: 028 8772 2225