Avian flu has wiped out 50.54 million birds in the United States this year, making it the country's deadliest outbreak in history, US Department of Agriculture data indicates.
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The deaths of chickens, turkeys and other birds represent the worst US animal-health disaster to date, topping the previous record of 50.5 million birds that died in an avian-flu outbreak in 2015.
Birds often die after becoming infected.
Entire flocks, which can top a million birds at egg-laying chicken farms, are also culled to control the spread of the disease after a bird tests positive.
Losses of poultry flocks sent prices for eggs and turkey meat to record highs, worsening economic pain for consumers facing red-hot inflation and making Thursday's Thanksgiving celebrations more expensive in the United States.
Mainland Europe and the United Kingdom are also suffering their worst avian-flu crises, and some UK supermarkets rationed customers' egg purchases after the outbreak disrupted supplies.
The US outbreak, which began in February, infected flocks of poultry and non-poultry birds across 46 states, USDA data shows.
Wild birds like ducks transmit the virus, known as highly pathogenic avian influenza (HPAI), through their faeces, feathers or direct contact with poultry.
"Wild birds continue to spread HPAI throughout the country as they migrate, so preventing contact between domestic flocks and wild birds is critical to protecting US poultry," USDA chief veterinary officer Rosemary Sifford said.
Farmers struggled to keep the disease and wild birds out of their barns after increasing security and cleaning measures following the 2015 outbreak.
In 2015, about 30 per cent of the cases were traced directly to wild bird origins compared to 85 per cent this year, the USDA told Reuters.
Government officials are studying infections at turkey farms in particular in hopes of developing new recommendations for preventing infections.
Turkey farms account for more than 70 per cent of the commercial poultry farms infected in the outbreak, the USDA said.
People should avoid unprotected contact birds that look sick or have died although the outbreak poses a low risk to the general public, the US Centers for Disease Control and Prevention said.
Australian Associated Press
