Silent Messengers: The Role of Wild Birds in Spreading HPAI H5 in Asia

In the last decade, highly pathogenic avian influenza (HPAI) has moved from being a seasonal threat to a year-round challenge for both poultry industries and wildlife conservation in Asia. Countries like China, Vietnam, India, Indonesia, South Korea, and Japan have all faced repeated outbreaks, often originating without clear human intervention. 

A recent study by Martelli et al. (2025), though based in Europe, offers crucial insights for Asian governments, veterinarians, and epidemiologists by identifying the wild bird species most closely associated with HPAI H5 transmission and emphasizing the role of eco-epidemiological modeling.

Why This Matters for Asia

Asia sits along major migratory bird flyways — the East Asian-Australasian Flyway (EAAF) and the Central Asian Flyway (CAF) — connecting breeding grounds in Siberia with wintering sites in Southeast Asia, the Indian subcontinent, and Australia. Wetlands, rice paddies, and aquaculture ponds are common stopovers for these birds — and unfortunately, also home to millions of free-ranging or low-biosecurity poultry farms.

This ecological overlap increases the risk of spillover events. However, much of the surveillance in Asia has historically focused on poultry-side monitoring, often neglecting the wild bird interface. The European study offers a model for shifting that focus — identifying bridge species that frequent both wetlands and farms, thereby playing a critical role in virus transmission.

Key Lessons from Europe with Relevance to Asia

Martelli et al. modeled 40 wild bird species near poultry farms in northern Italy and found that species like cattle egrets, little egrets, herons, pheasants, and moorhens had the strongest association with HPAI outbreaks. These are birds often found in Asia too — especially in India, China, and Southeast Asia — foraging in wetlands and agricultural lands side by side with ducks, chickens, and buffalos.

Interestingly, ducks and gulls, while still relevant, were not the strongest predictors of outbreaks in this study. The focus shifted to birds that traverse both wild and domestic zones — echoing patterns seen in Bangladesh’s Haor wetlands, Vietnam’s Mekong Delta, and China’s Poyang Lake region, where free-grazing ducks intermingle with wild migratory birds during seasonal flooding.

Surveillance Must Evolve in Asia

Current surveillance programs in Asia often center around Anseriformes (ducks and geese), but this study suggests expanding the net to include Ardeidae (herons and egrets), Galliformes (pheasants), and even corvids and passerines that live near human habitation. Many of these species are:

• Abundant across rural Asia
• Resident year-round, not just seasonal visitors
• Active in human-modified landscapes like rice paddies, garbage dumps, or fish farms

Moreover, the study uses species distribution models combined with outbreak data to build predictive risk maps — a technique that can be localized in Asian countries using eBird data, satellite imagery, and outbreak records.

Strengthening Asia’s Defenses

Here’s what Asia can learn and do:

1. Broaden wild bird surveillance: Include species not traditionally considered reservoirs, like cattle egrets and pheasants.
2. Integrate eco-epidemiology: Use mapping and modeling tools to predict where outbreaks might occur, based on bird movement and land use.
3. Reevaluate farm siting and biosecurity: Farms near wetlands or open water bodies need stricter controls.
4. Invest in cross-border coordination: Migratory birds don’t recognize national borders. India, China, and Southeast Asian countries must coordinate surveillance and response.

A One Health Wake-Up Call

Wild birds are more than innocent bystanders in the HPAI story. They are sentinels, transporters, and possibly even victims. Asia, with its dense human and animal populations, is a hotspot for zoonotic diseases. By bridging the knowledge gap at the wild–domestic interface, Asian nations can strengthen early warning systems, reduce poultry mortality, and protect public health.

Conclusion

The study by Martelli et al. underscores a pressing need: Asia must widen its surveillance lens. Rather than just watching the skies for ducks and geese, we must look around — at the egrets in our rice fields, the magpies in our mango orchards, and the pheasants in our forests. They may hold the keys to anticipating and preventing the next HPAI outbreak.

References

Martelli, L., Fornasiero, D., Martínez-Lanfranco, J. A., Spada, A., Scarton, F., Scolamacchia, F., Manca, G., & Mulatti, P. (2025). Exploring the Role of Wild Bird Species in the Transmission of Avian Influenza to Poultry. Transboundary and Emerging Diseases. https://doi.org/10.1155/tbed/2288535