Brown County case of bovine TB has state vet curious

State officials are investigating the origin of a steer that tested positive for bovine tuberculosis last month in Aberdeen.

A young, red feedlot steer tested positive for a new strain of bovine tuberculosis during a routine slaughter inspection at DemKota Ranch Beef, according to a U.S. Department of Agriculture report to the state's Animal Industry Board.

State Veterinarian Dustin Oedekoven said South Dakota has had other cases of bovine tuberculosis in the last year. They were in herds in two West River counties.

The strain of bovine tuberculosis found in Brown County is closely related to a strain that has been confirmed in Mexico, he said.

"We've found out from the National Veterinary Services Laboratory that the strain that was identified in that steer was not related to the cases we had in Tripp and Harding counties. Furthermore it has not been identified in the United States previously. It's a really strange presentation of bovine tuberculosis. The closest relative of this strain was in Mexico, which is not uncommon. That's where we see other related strains," Oedekoven said.

Since the steer was younger than 18 months, it was not required to have an identification tag.

"The group that went to slaughter that day was the last of a the group that was in that pen, and there were no other animals identified (with bovine tuberculosis) within that group," Oedekoven said.

"We don't know exactly which herd that steer came from. The feedlot owner had sourced animals from auction markets and there were multiple sellers. We're investigating those potential sales," he said.

Tuberculosis can infect both humans and animals and is transmitted through direct contact or respiratory secretions, Oedekoven said.

He said that around 30 percent of human tuberculosis cases in Mexico are due to region's different food consumption practices, which include drinking unpasteurized milk and eating soft cheeses.

"People that come from other countries, not only Mexico, may be at higher risk of tuberculosis. In some cases we may believe that tuberculosis has spread from people to animals, though that's difficult to prove," he said.

Most mammals can catch tuberculosis, a bacteria that attacks the lungs and causes illness, coughing and death.

There is a human vaccine, which is not commonly used in the U.S., but is in other counties where tuberculosis is common, according to the federal Centers for Disease Control.

Imported cattle tested

As many as 1.5 million cattle are imported to the U.S. each year.

"While they are tested prior to import, some of them are infected and it it's undetectable. It's not a food safety risk because of the food safety protections we have in our country. As far as I'm concerned there's not a lot South Dakotan producers can do to prevent it other than knowing your sources — don't interbreed your herds with Mexican breeding cattle," Oedekoven said.

"We're kind of scratching our heads as to why these strains are showing up in South Dakota," he said.

Cattle infected with bovine tuberculosis are killed.

"There's really no vaccine for bovine tuberculosis partly due to testing and eliminating infected animals. That's how that's happened over the years. Our main surveillance stream is slaughter channels. If they find those signs of tuberculosis they test the samples, and if we find a positive tuberculosis-infected carcass we do our best to go back to our herd of origin," Oedekoven said.

"The prevalence of tuberculosis in United States cattle populations is extremely low,' he said.

South Dakota was recognized as tuberculosis-free in 1982, though occasional cases are found, Oedekoven said.

The cases in Harding and Tripp counties involved adult livestock that had been culled to slaughter and were required to have identification tags, which helped officials quickly identify what herds they came from.

"This case is a little different in that it was in a feedlot steer. ... We'll make some determinations on what herds to test, which will be in the fall because a lot of them are out in the pasture," Oedekoven said.

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