Bovine tuberculosis found in South Dakota
A Harding County, South Dakota, ranch is under quarantine after three cows originating there were found to be infected with bovine tuberculosis.
All fenceline neighbors are under quarantine at this time, too, said South Dakota state veterinarian Dr. Dustin Oedekoven. A total of approximately 10,000 head of cattle are quarantined, he said.
Neighboring ranches will be out of quarantine if and when their herds test clean, he said. He doesn’t know at this time when the affected herd might be out of quarantine.
Every bovine animal in the affected herd has been tested, with some animals being euthanized and necropsied at the state diagnostic laboratory in Brookings.
Most of the animals that were put down were confirmed to be infected with the disease. The affected ranch has been compensated through USDA Animal and Plant Health Inspection Service (APHIS) for the euthanized animals.
The three cows that were initially traced back to the Harding County herd were found in two separate slaughter facilities within one week of each other, Oedekoven said.
“The cows were sold last fall – two through one western South Dakota market and another through a different western South Dakota market. Two went to one cow feedlot for about 90 days and the other went to another cow feedlot. They were slaughtered at two different Nebraska plants within a week and USDA inspectors found the lesions, sent samples to the lab, and TB was confirmed.”
Oedekoven said his team has not determined how TB was introduced into the Harding County herd but they are investigating a number of angles, as well as tracking where cattle have gone after leaving the affected ranch.
“How one of these investigations works — we test at all the adjacent herds and look at the affected herd’s records going back about five years. We look at purchases this herd has made and sales that this herd has made.” The affected ranchers have been helpful and cooperative, he said.
“They’ve been forthcoming with their neighbors and with helping us identify herds that might be at risk. We’ve got a lot of work to do but it’s not going to appear to affect the entire region. We’ll work through it systematically with the good information we’ve been able to gather,” Oedekoven said.
Neighbors, who don’t want to be identified, are praying for the affected ranch, even as they deal with the quarantine themselves, which prevents them from selling cull cows.
“My heart goes out to them. They are very good operators. They do everything right. They would never bring a cow on the place that didn’t meet their high standards. This could happen to anyone, nobody is pointing fingers. We’re sorry this had to happen because they’ve done everything right their whole lives,” a neighbor said.
Oedekoven said that some situations are lower risk than others. Calves from the affected ranch that were previously sold for feeding and slaughter, for example, are considered low risk, but are still tracked.
Bovine tuberculosis is not easily transmitted from one animal to another so the chance of even neighboring herds being greatly affected is small, Oedekoven said.
“Primarily we are interested in breeding animals because this is a chronic disease that takes some time to develop. We look at bull sales and where they purchased breeding females, all of those will be investigated,” he said.
Further investigation may help determine how the disease was introduced to the Harding County ranch. There are different strains of TB and genetic testing can reveal information that indicates the likely origin of that specific strain. For example, in a 2009 case of TB in South Dakota was identified as a strain that came from elk or deer, he said.
Even with this positive herd, South Dakota continues to be considered a TB–free state.
“The US has nearly eliminated bovine TB due to a cooperative eradication campaign. South Dakota has officially been recognized as free of the disease since 1982. There is no immediate effect to our state status. The last affected herd in South Dakota was identified in Hutchinson County in November 2011. Thorough investigation of this outbreak will help us maintain our free status with USDA,” he said. The status is important because South Dakota sends a lot of cows and calves out of state for feeding, he said.
Because the affected ranch has bought cattle from out of state, and sold cattle out of state, other states are already involved in the investigation, and quarantining and testing additional of herds is a real possibility, said Oedekoven.
Oedekoven said that all of the neighbors are quarantined, at least in part. Some neighboring ranches have cattle in more than one location that are not co-mingled. Only the cattle that have been in fenceline contact with the infected herd are under quarantine and are required to be tested.
Testing has not begun on neighboring herds, but will soon. Oedekoven’s office is aware of the burden this requirement puts on ranchers, particularly during calving season, and will work with ranchers’ schedules as much as possible, he said.
Some ranchers might want to wait until branding day to test, which is acceptable.
A ranch will not be released from quarantine until its herd has been tested and classified as TB free.
The ranchers will not be charged for the staff time or materials needed for testing, which must be done by a state or federal veterinarian. The ranchers’ time and labor and use of facilities needed to test their cattle will be their responsibility.
The Testing Process
The first TB test is a skin test, similar to a human one, said Oedekoven. “We would inject a small amount of tuberculin within the layers of skin, then we come back three days later, after the immune system has had time to respond. Swelling around the injection site is an indication that the animal may be infected and that further testing is warranted.” That injection is done in skin near the tailhead, called the caudal fold.
Some false positives are expected with the initial test, so a second test is done in the neck of any animals that tested positive initially. In the second test, two different kinds of tuberculin are injected and checked within three days.
If, after the two tests, the reaction indicates a positive result, the animal is euthanized and tissues are sent to the lab where testing will provide a definite answer, based on bacterial lesions in TB-positive cattle, Oedekoven said. TB infected cattle will often have visible nodules in their lungs or lymph nodes, he said.
Tri-State Livestock News reported last fall that 22,000 head of cattle in Canada were under quarantine and 10,000 at risk for euthanization after a Canadian cow was discovered to be infected with TB during a routine check at a United States slaughter plant. Forty operations were affected and 18 were high risk, the story said.
Oedekoven said he does not expect to have to quarantine all of Harding County.
“I don’t think there’s going to be a countywide restriction on movement,” Oedekoven said. “We want to move through this thoroughly to maintain our status nationwide.”
There is no vaccination for TB, said Dr. Oedekoven.
While he suggests that ranchers always keep a close eye on their cattle for health purposes and stay in contact with their local veterinarian, Oedekoven said ranchers don’t need to fear a sudden “outbreak” of TB.
The pathogen is spread from direct contact between animals or through feed bunks or waterers. It can be ingested or passed via respiratory channels. It won’t travel for miles, but tends to be spread when cattle are in close quarters, he said.
Cattle with TB are often slaughtered before showing clinical signs. “It is a chronic respiratory disease. Eventually it causes wasting away and death loss, but there are many other things that can cause that as well,” Oedekvoen said.
“Certainly if ranchers are seeing that kind of thing they should call the vet and assess the clinical health of their herd. A general awareness of the health of your livestock is important.”
Bovine TB is not a food safety threat, thanks to milk pasteurization and meat inspection programs.