Study Confirms H5N1 Spread Between Cows, Cats, Raccoon

Researchers found mammal-to-mammal transmission of highly pathogenic avian influenza H5N1 among dairy cows and other animals on affected farms.

Updated on Nov. 3, 2026 in COVID-19

Study Confirms H5N1 Spread Between Cows, Cats, Raccoon

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A study published July 25 in Nature confirmed transmission of highly pathogenic avian influenza H5N1 between dairy cows and to cats and a raccoon. Whole genome sequencing found no mutations that would enhance transmissibility of the virus in humans.

Why it matters

The findings show the virus can move between mammals on farms, which raises concern about how it could adapt over time. Officials and researchers are watching for any changes that could increase spread to people, as several human cases have already been reported.

The study relied on whole genome sequencing, modeling and epidemiological information, and the U.S. has reported 11 human H5N1 cases since April 2022. Researchers have not determined whether the virus may adapt in mammals to enable efficient transmission in humans.

The players

Nature

Nature is a leading international scientific journal that publishes peer-reviewed research across many fields.

The details

Researchers used sequencing and epidemiological data to trace virus transmission from infected cows in Texas to healthy cows on an Ohio farm. The virus also infected cats and a raccoon, most likely after they drank raw milk from infected cows, and wild birds found dead on affected farms were also detected. Infected cows showed reduced appetite, changes in fecal consistency, respiratory distress and reduced milk production, and pasteurization kills the virus.

January 2022: H5N1 infections were first detected in the U.S.
April 2022: The first U.S. human H5N1 case was reported.
July 25: The study was published in Nature.
Recent weeks: Four human H5N1 cases were reported in Colorado.

Big Picture

Whole genome sequencing of H5N1 samples from U.S. dairy herds has become the main tool for tracing how the virus moves between animals. This study extends that work by documenting spread among cows and to other mammals on the same farms.

Raw milk from infected animals can carry the virus, and pasteurization kills it. Readers who consume dairy products are not affected by the virus through pasteurized milk, according to the findings.

The takeaway

Pasteurization kills the H5N1 virus, which is a practical safeguard for dairy consumers. Continued sequencing of animal and human samples will show whether the virus changes in ways that matter for people.