Nevada detects new bird flu strain H5N1 D1.1 in cattle herds

At least four cattle herds in Nevada have tested positive for a strain of H5N1 bird flu never before seen in cows, state agriculture officials confirmed Wednesday. Reports of respiratory symptoms, such as coughing and sneezing, have been noted.

This bird flu strain, referred to as D1.1 by scientists, was previously linked to a fatal human case in Louisiana last year that resulted from exposure to sick birds. The D1.1 strain has recently become dominant among infections in wild birds and poultry flocks across North America.

Symptoms in humans infected with D1.1 have been observed to be more severe than the previous bird flu strain affecting cows, known as B3.13. The latter has led to only mild symptoms, including pink eye and fever, in humans who came into contact with sick cows.

Research indicates that B3.13 is less likely to cause severe illness in humans compared to other bird flu strains found abroad. However, other animals like pet cats have frequently died after exposure to food and milk contaminated with B3.13.

The discovery of the D1.1 bird flu strain in cows challenges earlier theories proposed by U.S. health and agriculture officials, which suggested that the virus's spillover into cows from wild birds was a rare occurrence.

All previously identified bird flu cases in cows since a spillover event in Texas in late 2023 were linked solely to B3.13, which officials noted as evidence that new variants were not continuously spreading to cows from birds.

The U.S. Department of Agriculture's Animal and Plant Health Inspection Service stated Wednesday, "The detection does not change USDA's HPAI eradication strategy," referring to the federal government's plan to combat the ongoing surge of highly pathogenic avian influenza (HPAI).

Alongside the human health threat, the spillover of D1.1 from wild birds into poultry has caused a significant increase in egg prices nationwide.

As of now, nearly a thousand cow herds have been confirmed as infected by bird flu across 16 states, with the most recent cases reported in California.

The four recently infected cattle herds in Nevada were identified in Churchill County, as confirmed by a spokesperson from the state's Agriculture Department.

A herd in Nye County also tested positive for bird flu in December but was affected by the B3.13 strain.

In addition to the newly identified herds, two other herds in Churchill County are currently under quarantine while awaiting laboratory results from the USDA.

Ciara Ressel, spokesperson for the Nevada Agriculture Department, remarked, "Symptoms of H5N1 D1.1 have been similar to the detections of B3.13, including fever, reduced feed consumption, reduced milk production, and mild respiratory signs (coughing, sneezing, runny nose)."

The detection of these herds was confirmed through a state investigation after a silo that had received milk from these cows tested positive for the virus.

The USDA continues its collaboration with the Nevada Department of Agriculture to conduct on-farm investigations, testing, and to gather additional epidemiological information to help control the spread of the disease.

It remains unclear how many workers in Nevada may have been exposed to the D1.1 strain while working with the affected cows.

A spokesperson for Nevada's health department redirected comments to the Central Nevada Health District, which did not respond immediately.

The Centers for Disease Control and Prevention (CDC) reported that out of the 67 confirmed human bird flu cases since 2024, 40 have been linked to exposure to dairy cows infected with the virus. Most other cases arose from exposure to infected poultry.

Last month, Nevada's Agriculture Department issued a statement noting that the CDC still considers the risk to humans to remain low, while they work in conjunction with state and county health officials to ensure human health and safety.

A CDC spokesperson did not provide comments regarding whether the spillover of D1.1 alters that risk assessment.

State veterinarian Peter Rolfe emphasized, "It is critical that animal health biosecurity practices are enhanced to help prevent the spread of disease and protect animal and worker safety."