Dairy cows in Nevada have been infected with a new form of bird flu, the U.S. Department of Agriculture announced on Wednesday.
The new strain, known as the D1.1 genotype, was discovered through an agency testing milk in December. The D1.1 strain was the predominant genotype among wild birds this past fall and winter and has also been found in poultry.
Wild birds likely transmitted the second strain to cattle in Nevada, according to officials who suggest farmers should ramp up safety measures to contain the outbreak in Nevada from spreading to other states.
The H5N1 virus has reduced milk output in cattle, pushed up egg prices by wiping out millions of hens, and infected nearly 70 people since April as it has spread across the country.
“We’re seeing the H5N1 virus itself be smarter than all of us,” said Beth Thompson, South Dakota’s state veterinarian. “It’s modifying itself so it’s not just staying in the poultry and the wild waterfowl. It’s picking up a home in the mammals.”
According to the American Veterinary Medical Association, common clinical signs in affected cows include low appetite, reduced milk production, and abnormal appearance of milk (thickened, discolored). Lactating cows have been most highly affected, and signs of illness have been reported in less than 10% of cows within a herd.
While bird flu is associated with high morbidity and mortality in birds, this hasn’t been the case for dairy cattle. Most affected animals reportedly recover with supportive treatment, and the mortality/culling rate has been low at 2% or less on average.
- Of the 67 Americans known to have become ill with H5N1 so far, the only one who died was infected with the D1.1 version. That person died in January and had cared for sick and dying birds in Louisiana, and was older than 65.
- Another in Canada, a 13-year old girl, whose only risk factor was obesity, became severely ill and was placed on life support, but did recover.
- Bird flu is best adapted to infecting birds, but the virus gained mutations during the course of infection that might allow it to better infect people.
