With chickens becoming the most widely produced land-based animals globally, avian influenza poses a serious threat to poultry production, public health and food security. Rapid expansion of chicken production in South and Southeast Asia has created increased opportunities for avian influenza viruses to emerge and evolve, including strains that can infect humans.

While live bird markets are well-known hotspots for transmission, much less is understood about the wider production and distribution system. In Viet Nam, practices such as trading live chickens and slaughtering birds at the point of sale further increases the risk of human exposure. However, there is limited data linking farms, distribution facilities and points of sale which has left gaps in understanding where infection risk is highest – highlighting the need for surveillance across the entire poultry network.

This study was conducted by the RVC and with project partners in Viet Nam, France and Hong Kong to carry out a cross-sectional investigation of chicken production and distribution systems in northern Viet Nam. The researchers collected 1,682 samples across 50 farms and 52 distribution facilities in four provinces, including retail and wholesale markets, small-scale slaughter points and industrial slaughterhouses. To understand how chickens moved through the system, the researchers also interviewed farmers, traders and facility operators. This data was used to trace chicken movements and analyse the poultry supply chain as a connected network, allowing researchers to identify where chickens from different sources were most likely to mix, as well as testing for the presence of avian influenza viruses.

The study revealed clear differences in the presence of avian influenza viruses across the poultry production and distribution system. Two virus types were examined: A(H5N1), which is a highly pathogenic virus associated with severe disease; and A(H9N2), a low pathogenic virus which typically causes less severe disease in chickens. Both virus types can harm poultry and potentially infect humans directly or can combine with other influenza viruses to form new strains. Only one chicken tested positive for A(H5N1), whereas A(H9N2) was detected in 11% of all sampled chickens, with higher prevalence in distribution facilities than on farms.

Differences were also observed between facility types along the distribution chain. The prevalence of A(H9N2) in distribution facilities was approximately five times higher than on farms, indicating increasing virus detection as chickens moved through the supply chain. Among facility types, the highest prevalence was detected at informal slaughter points, followed by retail markets, with a substantially lower prevalence observed in slaughterhouses and wholesale markets. These latter facilities are prioritised for upgrade through the Vietnam Avian and Human Influenza Preparedness (VAHIP) programme, suggesting that improved infrastructure and biosecurity measures may be effective in reducing virus circulation. In contrast, retail markets and small-scale slaughter points showed high virus prevalence. As the most commonly used outlets for purchasing chickens, the study also highlights the increased risk of virus exposure closer to the point of sale.

These findings indicate that avian influenza surveillance and mitigation strategies in Viet Nam should extend beyond large industrial slaughterhouses and wholesale markets to include smaller, widely used chicken distribution facilities, as well as the farms that supply them.

By identifying points along the poultry supply chain where virus circulation is most likely to occur, this study provides an evidence base for more inclusive and targeted control strategies that better reflect how chickens are produced, traded and purchased in Viet Nam. For example, given the continued pandemic potential of avian influenza viruses for both poultry and humans, these findings suggest that effective surveillance be paired with safer food production and distribution practices.

This study was funded by the UKRI GCRF One Health Policy Hub; the French National Research Agency; the French Ministry of Higher Education and Research; the UK Department for the Environment, Food and Rural Affairs (Defra); and the devolved Scottish and Welsh governments. It forms part of the One Health Poultry Hub, which works in collaboration with the RVC, the National Institute of Veterinary Research in Viet Nam and the Animal and Plant Health Agency in the UK.