The US state agriculture officials have confirmed that cattle in Nevada have tested positive for a strain of H5N1 bird flu that has never before been seen in cows. The infected cows are showing respiratory symptoms like coughing and sneezing.

According to experts, the detection indicates that distinct forms of the virus known as Type A H5N1 have spilt over from wild birds into cattle at least twice. It is now raising new questions about the wider spread and the difficulty of controlling infections in animals and the people who work closely with them.

Called D1.1 by scientists, the new bird flu strain has also been linked to a fatal human case in Louisiana last year after exposure to sick birds. The D1.1 strain has emerged in recent months to dominate infections in wild birds and poultry flocks across North America.

Symptoms seen in humans infected by D1.1 have been more severe than the previous bird flu strain that has been spreading in cows. That strain, called B3.13, has led to only mild symptoms, like pink eye and fever, in humans infected after contact with sick cows.

Studies say that B3.13 is less likely to result in severe disease for humans, unlike other bird flu strains overseas. However, the risk is different for other animals, like pet cats, which have recently died after exposure to food and milk contaminated with B3.13.

The discovery of the D1.1 bird flu strain's spread in cows also upends previous theories floated by US health and agriculture officials that the spillover of the virus into cows from wild birds was a rare, one-off event. All cases of bird flu in cows since a spillover in Texas in late 2023 had previously been linked only to B3.13, which officials have cited as evidence that new variants of the virus were not repeatedly spreading into cows from birds.

Till now, at least 67 people in the US have been infected with bird flu, mostly those who work closely with dairy or cattle, according to the US Centers for Disease Control and Preve"The detection does not change USDA's HPAI eradication strategy," said the US Department of Agriculture's Animal and Plant Health Inspection Service, also adding that the federal government plans to try to stop the unprecedented surge of highly pathogenic avian influenza or HPAI, in recent years.

In addition to the human health threat posed by the virus, the toll claimed by spillovers of the D1.1 from wild birds into chickens has also spiked egg prices across the country.

According to officials, as of now, it is not clear how many workers in the state may have been exposed to the D1.1 strain after working with sick cows. The Centers for Disease Control and Prevention say that 40 out of the 67 confirmed human bird flu cases since 2024 have been linked to exposure to dairy cows sick with the virus. Most of the others have been the result of exposure to infected poultry.

The CDC maintains that the risk to humans remains low, and it is working with state and county health officials to protect human health and safety.

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