The bird flu in the United States of America is showing no sign of dying down.
A variant of H5N1 bird flu that has circulated widely in wild birds — and several instances led to severe illness in humans — has turned up in dairy cattle for the first time. The findings were relayed in a short update from the U.S. Department of Agriculture, which traced the new variant back to dairy herds in Nevada.
The state agriculture officials confirmed, at least four cattle herds in Nevada have tested positive for a strain of H5N1 bird flu never before seen in cows with respiratory symptoms like coughing and sneezing have been reported.
That bird flu strain, called D1.1 scientists that has emerged in recent months to dominate infections in wild birds and poultry flocks across North America, was also linked to a fatal human case in Louisiana last year after exposure to sick birds.
What is the D1.1 strain?
D1.1 is a strain of the avian influenza virus (HPAI) that was first detected in North American birds in the fall and winter of 2024.
The discovery of the D1.1 bird flu strain’s spread in cows also upends previous theories floated by U.S. health and agriculture officials that the spillover of the virus into cows from wild birds was a rare, one-off event.
For humans infected by the D1.1 strain, the symptoms in them 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.
The B3.13 strain:
However, research suggests that B3.13 is less likely to result in severe disease for humans, unlike other bird flu strains overseas. The risk is different for other animals, like pet cats, which have frequently died after exposure to food and milk contaminated with B3.13.
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.
Citing the federal government’s plan to try to stop the unprecedented surge of highly pathogenic avian influenza, or HPAI, in recent years, the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service said, “The detection does not change USDA’s HPAI eradication strategy.”
Apart from the human health threat posed by the virus, an unprecedented toll claimed by spillovers of the D1.1 from wild birds into chickens has driven up egg prices across the country. As per the USDA, nearly a thousand cow herds have been confirmed infected by bird flu to date, with detections across 16 states, while most recent cases have been in California.
Bird flu was also reported in December from a herd in the state’s Nye County, though those cows ended up testing positive for the B3.13 strain of the virus. The Nevada spokesperson said that two additional herds in Churchill County have also now been placed under quarantine, pending laboratory results from the USDA.
Regarding the cows’ symptoms, the Nevada Agriculture Department spokesperson said, “Symptoms of H5N1 D1.1 have been similar to the detections of B3.13. These include fever, reduced feed consumption, reduced milk production and mild respiratory signs (coughing, sneezing, runny nose).”
Those herds were confirmed to have been infected as the result of a state investigation, the USDA said, after a silo that had received milk from the cows tested positive for the virus. As per USDA, “USDA APHIS continues to work with the Nevada Department of Agriculture by conducting additional on-farm investigation, testing, and gathering additional epidemiological information to better understand this detection and limit further disease spread.”
However, it is unclear how many workers in the state may have been exposed to the D1.1 strain after working with those sick cows.
What is bird flu?
Bird flu, also known as avian influenza, is a viral infection that primarily affects birds but can also infect humans and other animals.
H5N1 bird flu, also known as highly pathogenic avian influenza (HPAI), is a subtype of the influenza A virus that can infect birds, mammals, and humans.
Causes: Bird flu is caused by the influenza A virus, which is present in many bird populations. There are many different strains of the virus, which can be classified as either low pathogenic (LPAI) or high pathogenic (HPAI).
Symptoms:Symptoms of bird flu can range from mild to severe and include fever, cough, muscle aches, eye redness, and difficulty breathing. In severe cases, complications like pneumonia or organ failure can occur.
Transmission: Bird flu spreads between wild and domesticated birds, and can be transmitted to humans through close contact with infected animals or contaminated surfaces. There is no clear evidence that bird flu can spread from person to person, but it may have happened in rare cases.
