Brucellosis continues to show up in Wyoming, efforts maintain marketability
Riverton – Northwest Wyoming’s wildlife reservoir of brucellosis continues to create problems for cattle producers, and Wyoming State Veterinarian Jim Logan explained to producers at Fremont County Farm and Ranch Days that two new cases were seen in the state in late 2015.
Currently, Wyoming has two cattle herds that are quarantined due to brucellosis.
“Montana only has one bison herd under quarantine, and Idaho doesn’t have any currently,” Logan said. “In Wyoming, we were able to release a bison herd in Park County that had been under quarantine since 2010.”
Cases of brucellosis
With cases of brucellosis occurring in 1988, 2003, 2004, 2008, 2010 and 2011, Logan noted that 2015 also showed two new cases of brucellosis.
Shortly after a domestic bison herd was released from quarantine, an infected beef cow was found in a Park County herd. The herd was quarantined. Testing showed that only one cow in the herd was infected. The cow was removed, and the herd has successfully completed two negative, whole-herd tests.
Less than a week after the Park County herd was quarantined, a veterinarian at one of Wyoming’s livestock markets found a suspect positive cow.
“The suspect positive was not Brucella abortus,” Logan said. “Confirmatory testing showed that another bacterial infection tripped the test and skewed results.”
“Three days later, another suspect cow was found in Sublette County,” he continued. “There were five cows in a group of cull cows that were positive, and additional testing showed six more positive animals.”
One negative, whole-herd test has been conducted to this point, and Logan added that no additional cows were found from herds that had commingled or had fenceline contact with infected herds.
“We are going to see this disease crop up from time to time in cattle in the Greater Yellowstone Area,” Logan said, noting that the wildlife reservoir means that total eradication will be difficult.
“Brucellosis is a bacterial disease caused by Brucella abortus,” Logan explained. “It was recognized as a big problem in this country in the early 1900s, and it is still a problem in the Greater Yellowstone Area.”
Brucella bacteria are shed from infected animals at the time of birthing, and bacteria are transmitted orally or by inhalation.
“Any animal that licks or sniffs the fluids, placenta or an aborted fetus can become infected with Brucella,” he said, noting that, if a live calf is born to an infected animal, that calf can also carry the bacteria. “Brucellosis is a chronic disease. Once an animal is infected with Brucella, it is considered to be a lifelong carrier of the bacteria.”
Logan explained that many producers are aware that brucellosis causes abortions, but it is also possible to see live calves born to infected animals.
“Typically, if an infected calf reaches full-term, it is alive at birth, but it probably won’t survive more than a few days,” he said. “The bacteria affects the lungs in the baby, so it dies after showing signs of pneumonia. Ranchers treat with antibiotics, and the calf dies showing signs of pneumonia.”
Because the ranchers don’t suspect brucellosis, they often don’t call the vet, and brucellosis is able to persist in the herd.
As a result of the wildlife reservoir in the Greater Yellowstone Area, Logan said that temporal and spatial separation are key to reducing impacts from the disease.
“Temporal separation means to keep cattle separated from wildlife at the time that brucellosis could be transmitted,” he explained. “The key period we are worried about brucellosis transmission in February through June.”
In February, March and April, wildlife infected with brucellosis are likely to abort their calves. Those who deliver full-term calves are expected to deliver in May and June.
While focusing on the key timing, Logan also noted that keeping cattle as far away from the wildlife reservoir as possible spatially is also important.
“It is difficult to keep cattle away from wildlife sometimes,” he said, “especially when people depend on public lands for at least seasonal grazing.”
“The good thing is that summer, fall and early winter are not considered significant times for risk of exposure,” Logan noted.
Logan also noted that surveillance and management are vital to preventing the disease in cattle.
“Surveillance and management includes brucellosis testing,” he said. “I’m not suggesting that people everywhere in the state need to test for brucellosis, but within the boundaries of the Designated Surveillance Area (DSA), it is important.”
He continued, “At this point, we are not aware of a big risk factor in wildlife outside of the DSA, with the exception of Big Horn and Sheridan counties where we know there are infected elk.”
The Wyoming Livestock Board has designated Big Horn and Sheridan counties as an “Area of Brucellosis Concern,” and therefore surveillance testing there is important but is currently voluntary, Logan added.
Though Big Horn and Sheridan counties are not included in the boundaries of the DSA, seven hunter-killed elk were found to be positive for brucellosis during the 2012-14 hunting seasons. 2015’s hunting season did not find any new positives.
“We can also vaccinate for brucellosis,” Logan said. “Vaccination for brucellosis is mandatory in Wyoming for all heifers that are going to be kept for breeding purposes.”
Logan added that vaccination, however, is not 100 percent effective, though it is helpful in mitigating risk.
“Every herd, with the exception of the first one in 1988, has been 100 percent vaccinated for brucellosis,” he said. “Vaccination is another tool, and it reduces the chance of infection and abortion. It is not 100 percent. We have to combine vaccination with appropriate management to be effective.”
Saige Albert is managing editor of the Wyoming Livestock Roundup and can be reached at firstname.lastname@example.org.