The bird flu outbreak in U.S. livestock herds is believed to have reached Minnesota on Thursday, when the state Animal Health Board said a farmer reported more than 40 cows showing signs of fever.
The animals were tested on Monday and the U.S. Department of Agriculture (USDA) National Veterinary Laboratories confirmed the positive test.
The entire herd has been quarantined for 30 days to reduce the risk of the virus spreading off the farm and milk from the sick cows being thrown away, the Minnesota Board of Agriculture said.
State Veterinarian Brian Hoefs said the herd was recovering, noting that “it was only a matter of time before this detection reached our doorstep.”
An outbreak of H5N1 bird flu in multi-state dairy cows in herds in Kansas and Texas was first reported in March. This was the first time that bird flu viruses were found in cattle.
The following month, the US Centers for Disease Control and Prevention confirmed one person had contracted H5N1 from exposure to dairy cows believed to be infected in Texas. Last month, the agency reported additional cases in people exposed to infected livestock.
Since late March, more than 80 dairy herds have reportedly been infected in 11 states three dairy workers testing positive, including two in Michigan. The virus is not believed to have acquired the ability to transmit infections between people.
However, health officials in Mexico confirmed last month a fatal case of human infection with bird flu H5N2, a virus reported in poultry in Mexico. The World Health Organization estimates the current risk of this virus to the general population as low.
Confirmation that H5N1 has reached Minnesota will likely prompt more testing, Hoefs told Reuters. “Once this news gets out, it will prompt other farms to do the testing if they were previously on the fence,” he said.
Other states that have reported infected herds outside of Texas, Kansas and Minnesota include Colorado, Idaho, Iowa, Michigan, New Mexico, North Carolina, Ohio and South Dakota.
The USDA has said the vast majority of cows recover from the disease. Reuters found that some cows with bird flu have died or been slaughtered by farmers after failing to recover, suggesting that the outbreak in cows could take a greater economic toll than outbreaks in poultry because the cattle are more expensive to raise.
The agriculture agency said last month that bird flu virus particles had also been found in beef tissue comes from a dairy cow that was slaughtered for meat, but that animal’s meat did not end up in the food supply.
In South Dakota, a dairy farm with 1,700 cows sent a dozen animals to slaughter after they failed to recover from the virus, and killed another dozen that suffered secondary infections, the news agency found.
“You get sick cows from one disease, and that creates a domino effect for other things, like routine pneumonia and digestive problems,” says Russ Daly, a veterinarian and professor at South Dakota State University.
Michigan has more confirmed livestock infections than any other state. In Colorado, dairy farms have reported that cows with bird flu have been culled because they did not return to milk production. Meghan Harshbarger, spokesperson for the Ohio Department of Agriculture, said infected cows were usually due to secondary infections.