USDA Reports Second Bird Flu Spillover into U.S. Cattle

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USDA Reports Second Bird Flu Spillover into U.S. Cattle \ Newslooks \ Washington DC \ Mary Sidiqi \ Evening Edition \ A new strain of H5N1 bird flu has been detected in dairy cattle in Nevada, marking the second known spillover of the virus from wild birds to cows. Scientists warn that the emergence of multiple variants raises concerns about wider transmission and potential risks to humans. USDA officials plan to release genetic data on the new strain as researchers assess its spread and impact.

New Bird Flu Strain in Nevada Dairy Cattle: Quick Looks

Second Bird-to-Cow Transmission: USDA confirms a new H5N1 strain, D1.1, in Nevada dairy cattle, marking at least the second known spillover from wild birds to cows.
Distinct from Previous Variant: The D1.1 strain differs from the B3.13 variant, which has infected over 950 herds in 16 states since late 2023.
Linked to Human Cases: The D1.1 strain was tied to the first U.S. death from bird flu in Louisiana and a severe illness in Canada.
Raising Concerns Over Spread: Scientists warn the emergence of multiple strains could indicate more frequent transmissions and difficulty controlling outbreaks.
USDA Expanding Testing: The virus was detected through a milk surveillance program, highlighting the importance of ongoing monitoring in livestock.
Potential Pandemic Risks: Experts caution that failure to track and contain the virus could lead to dangerous mutations, increasing the risk of human-to-human transmission.
USDA to Release Genetic Data: Officials plan to publish the virus’s genetic sequences to determine whether it has been circulating undetected for months.
Call for Transparency: Scientists urge the government to share data quickly, stressing that understanding the virus’s evolution is critical for public health security.

Deep Look

A newly identified strain of H5N1 bird flu has been detected in dairy cattle in Nevada, marking the second time the virus has spilled over from wild birds into U.S. herds. The discovery, announced Wednesday by the U.S. Department of Agriculture (USDA), has renewed concerns about the virus’s spread, its impact on both livestock and humans, and the challenges of containing outbreaks.

The new strain, known as D1.1, is distinct from B3.13, the bird flu variant that has been circulating in dairy cattle since late 2023. While the earlier variant has infected more than 950 herds across 16 states, the emergence of D1.1 suggests that bird-to-cow transmission has occurred at least twice—raising questions about how frequently such spillovers may be happening undetected.

Experts Warn of Increased Risk and Wider Spread

For months, scientists have debated whether bird flu’s transmission from birds to cattle was an isolated event or part of a larger, ongoing risk. The new case in Nevada challenges earlier assumptions.

“I always thought one bird-to-cow transmission was a very rare event. Seems that may not be the case,” said Richard Webby, an influenza expert at St. Jude Children’s Research Hospital.

Scientists emphasize the importance of continued surveillance and testing to track the virus and prevent further outbreaks. The Nevada case was identified through a USDA milk surveillance program launched in December to detect the virus in dairy herds.

Angela Rasmussen, a virologist at the University of Saskatchewan, who helped identify the first cow infections, stressed the need for ongoing monitoring. “Now we know why it’s really important to test and continue testing,” she said.

Link to Human Cases and Pandemic Concerns

The newly identified D1.1 strain is concerning not only because of its appearance in cattle but also because of its connection to severe human illness. This strain was linked to:

The first U.S. death from bird flu, in January 2024, when a person in Louisiana died after severe respiratory complications following contact with infected birds.
A severe illness in Canada, where a teen girl in British Columbia was hospitalized for months after contracting the virus from poultry.

In the U.S., at least 67 people have been infected with bird flu, primarily farm workers who have close contact with dairy cows or cattle. While most cases have been mild, experts worry that further mutations could lead to more serious infections and human-to-human transmission.

Michael Worobey, an evolutionary biologist at the University of Arizona, warned that failure to track the virus properly could have catastrophic consequences. He noted that if D1.1 had been circulating in cattle for months undetected, it could already be more widespread than currently known.

“A couple of months is a long time not to detect it,” Worobey said. He urged federal officials to immediately share genetic data on the new strain, emphasizing that understanding its evolution is critical to preventing a potential pandemic.

“It’s a vital part of national security, global security, the well-being of people, of animals, and of businesses in the U.S.,” Worobey added.

USDA to Release Genetic Data on New Bird Flu Strain

To better understand the risks posed by D1.1, the USDA announced plans to publish genetic sequences of the virus in a public database later this week. Researchers will use the data to determine whether this strain recently jumped from birds to cattle or has been circulating undetected for a longer period.

Key Questions Scientists Hope to Answer:

How does D1.1 differ genetically from B3.13?
Did it originate from a separate bird-to-cow transmission event?
How easily does it spread between animals, and could it mutate to infect humans more efficiently?

Ongoing Efforts to Contain the Spread

As new bird flu variants continue to emerge, federal and state agricultural officials are increasing monitoring efforts in livestock and dairy farms. The goal is to limit the virus’s impact on food production and prevent further transmission to humans.

The discovery of a second H5N1 spillover event raises urgent questions about how bird flu spreads among species and whether it could evolve into a more dangerous form. Experts warn that a lack of transparency and slow responses to emerging diseases could increase the risk of a global health crisis.

For now, continued testing, data-sharing, and early intervention will be crucial in managing the spread of H5N1 and minimizing its potential impact on public health and the agricultural industry.