Highly pathogenic avian influenza, or H5N1, has been circulating the globe since 1996. The virus has grown more deadly to birds since it started spreading in North America in 2021. The disease spreads quickly among birds, and is nearly always fatal for poultry raised on large commercial farms.
In late March of this year, federal authorities recorded the first ever cases of H5N1 in dairy cows in Texas. It has since spread to 51 herds in nine states, leading to new regulations for testing and transporting cattle. The virus has also spread among wildlife, including walruses, polar bears, and foxes.
For over two years, more than 90 million commercially raised birds have been affected by the virus. More than 600,000 backyard flocks — which include poultry used for a wide range of purposes, such as breeding or fighting cocks — have also been affected.
And since February 2022, more than 83 million farmed chickens and turkeys have been killed in the U.S. as a way to stem the spread, according to the USDA.
A dairy worker in Texas tested positive for H5N1 in March, the second confirmed case in humans in the U.S. and the first cow-to-human transmission. In 2022, a poultry worker contracted the virus in Colorado.
The CDC considers the risk for human transmission low, according to a statement released by the agency, and continues to monitor the situation. This includes testing wastewater levels of influenza A, of which H5N1 is a subtype.
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