PIERRE, S.D. (AP) — South Dakota officials are trying to stop the spread of a strain of bovine tuberculosis discovered in a Harding County cattle herd.

It’s the first case of bovine tuberculosis in the state in six years. So far 41 infected animals have been identified, the Capital Journal reported.

Thirteen neighboring ranches were quarantined, six of which have since been released. State agriculture officials said the remaining seven still have testing to complete.

Wildlife officials also are testing deer, pronghorn, possums, raccoons, coyotes and badgers in the area.

The National Veterinary Services Laboratory in Iowa identified the strain of bovine tuberculosis as nearly identical to one previously only seen in dairy cattle in central Mexico.

Officials aren’t sure how it entered South Dakota, but state veterinarian Dustin Oedekoven thinks there are at least two possibilities.

“One, it came with cattle. A million to a million-and-a-half cattle are imported from Mexico to here. They’re all tested and inspected for animal health issues,” he said. “We also have additional test requirements if they enter from Mexico into South Dakota. We don’t know if these cattle are of Mexican origin. It’s a possibility, but it’s a long shot.”

Oedekoven said the second possibility is that the tuberculosis was brought in by people, which can be possible due to the fact that it can infect humans.

All animals that tested positive on the initial herd test were removed from the herd. Oedekoven recommended that herds with infected animals be depopulated or moved to slaughter. He said the cattle ranchers would be paid by the U.S. Department of Agriculture for the loss of their animals.