The U.S. poultry industry is more than three years into an outbreak of highly pathogenic avian influenza (HPAI) with no clear end in sight, and understanding what fuels transmission has become an operational priority for commercial producers. Erica Spackman, acting research leader at USDA’s National Poultry Research Center, told attendees at the 2026 Georgia Precision Poultry Farming Conference that the virus behind the current wave has distinct genetics and biology that complicate control efforts. Producers and researchers are focusing on where the virus persists in the environment and how it moves from wild reservoirs into houses and barns.
Spackman said current field isolates are far more infectious in poultry than some previous strains, meaning it takes a much smaller exposure to cause infection. Laboratory comparisons show these isolates can require roughly a thousand times less virus to infect chickens and turkeys, with some samples appearing even more infectious. 1,000× smaller infectious dose captures the scale of that change and the challenge it poses for standard biosecurity measures.
Wild waterfowl are the primary source of HPAI pressure on commercial operations, but researchers point to a narrower group within that category as the main reservoir. Dabbling ducks — mallards and other puddle ducks — commonly carry the virus without showing disease, continually seeding the landscape. Dabbling ducks reservoir highlights the species most implicated in maintaining and spreading viral pressure near poultry sites.
Environmental reservoirs
The virus can survive for extended periods in surface water, with experiments showing persistence at common seasonal temperatures measured in months rather than days. Field sampling from multiple U.S. locations has demonstrated that virus in natural water bodies can remain infectious long enough to expose returning waterfowl the following season. That means ponds, drainage ditches and low-lying runoff areas close to farms represent ongoing environmental risk that must be considered in site assessments.
Small mammals and birds that move between wetland habitat and farmyards are under investigation as possible bridging hosts. Rodents, skunks, raccoons, sparrows and starlings are frequently found on infected premises; in many cases it is unclear whether they acquired infection from poultry or served as mechanical carriers into houses. House flies can also carry virus on their bodies or briefly in their digestive tracts, and some fly species are capable of traveling more than a mile per day, which raises the prospect of short-range movement of infectious material between duck habitat and poultry facilities.
Dairy link
Detection of HPAI in dairy cattle introduced an unexpected transmission pathway that producers now watch closely. The virus can replicate in the bovine mammary gland and researchers have recovered very high concentrations of infectious virus in raw milk samples early in infection. Up to 10 billion particles per milk sample was reported in early infection cases, and circumstantial and genetic evidence has tied some poultry infections to nearby dairies where untreated waste milk was land-applied. Waste-milk handling varies widely and the volumes involved make effective treatment and disposal a practical challenge for some operations.
Researchers and industry stakeholders continue to prioritize on-farm biosecurity, environmental management of surface water, pest control and careful handling of livestock byproducts as the core actions to reduce transmission risk. An interactive map of HPAI cases in commercial poultry flocks across the United States, Mexico and Canada is available at WATTPoultry.com.
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