Nevada agriculture officials have announced the detection of a highly pathogenic H5N1 bird flu strain—known as D1.1—in at least four cattle herds, the first documented cases of this particular variant in cows. The state’s Department of Agriculture confirmed on Wednesday that the affected animals showed respiratory symptoms, including coughing and sneezing.
A Novel Strain Tied to Human Cases
The D1.1 strain of H5N1 has been drawing heightened concern since it was linked to a fatal human infection in Louisiana last year, following exposure to sick birds. In recent months, D1.1 has become the dominant form of H5N1 affecting wild birds and poultry flocks across North America.
Previous U.S. cases of H5N1 in cattle have involved a different strain, B3.13, which has typically led to mild symptoms—such as pink eye and low-grade fever—in humans who had contact with infected cows. However, pet cats exposed to B3.13 through contaminated milk or food have frequently suffered fatal outcomes, indicating the virus’s variable impact on different species.
Changing Perspectives on Spillover
Until recently, health and agriculture officials believed the spillover of H5N1 from birds into cows was a rare event. All known cattle infections since a 2023 outbreak in Texas had been associated solely with the B3.13 strain, suggesting the virus was not frequently crossing over from wild birds into livestock.
The new findings in Nevada challenge this assumption, revealing multiple herds infected by D1.1 and raising questions about how the strain might spread further among farm animals.
Despite the emergence of this novel strain in cattle, the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (USDA APHIS) stated that “the detection does not change USDA’s HPAI eradication strategy,” which aims to curb the ongoing surge of highly pathogenic avian influenza (HPAI).
Economic and Public Health Concerns
The discovery of D1.1 in cows adds to mounting worries about the virus’s impact on both agriculture and public health. Nationwide, D1.1-related outbreaks in poultry have driven up egg prices and strained production. According to the USDA, nearly 1,000 cattle herds across 16 states have tested positive for bird flu, with California seeing the majority of recent cases.
In Nevada, the four newly identified D1.1-infected herds are located in Churchill County. An earlier outbreak in December involved a herd in Nye County that tested positive for the B3.13 strain. Two additional herds in Churchill County are now under quarantine while officials await confirmation from USDA laboratories.
“Symptoms of H5N1 D1.1 have been similar to the detections of B3.13,” noted Ciara Ressel, spokesperson for Nevada’s Agriculture Department. “These include fever, reduced feed consumption, reduced milk production, and mild respiratory signs (coughing, sneezing, runny nose).”
The USDA adds that a silo receiving milk from infected cows tested positive for the virus, prompting further on-farm investigations, testing, and epidemiological studies.
Human Exposure and Ongoing Monitoring
It remains unclear how many workers in Nevada might have been exposed to D1.1 through contact with infected herds. The state’s health department referred inquiries to the Central Nevada Health District, which did not immediately respond to requests for comment.
According to the Centers for Disease Control and Prevention (CDC), 40 of the 67 confirmed human bird flu cases since 2024 have been traced to exposure to sick dairy cows. Most other infections have been linked to contact with infected poultry. While the CDC has consistently characterized the risk to the general public as low, it has not issued a specific update regarding the emergence of the D1.1 strain in cattle.
Heightened Biosecurity Measures Urged
Nevada’s Agriculture Department underscores the importance of stringent biosecurity and close collaboration with county and federal health agencies to safeguard both animal and worker health. “It is critical that animal health biosecurity practices are enhanced to help prevent the spread of disease and protect animal and worker safety,” said State Veterinarian Peter Rolfe.Officials continue to investigate the outbreak, implement quarantine measures, and conduct testing to contain further transmission. While efforts to eradicate HPAI remain a top priority, the appearance of the D1.1 strain in cattle adds a new dimension to managing bird flu’s evolving threat to both the agriculture sector and public health.