Keeping brucellosis at bay in U.S. cattle
November 13, 2014
As of today, the U.S. cattle herd is brucellosis-free. Producers, wildlife managers, veterinarians and researchers are doing what they can to make sure it stays that way.
But it's not easy.
In the early 20th century, brucellosis affected, to some extent, about 70 percent of all cow herds in the U.S. With an improved understanding of the disease, testing, vaccines and management, that number has been reduced to only occasional cases in the Greater Yellowstone Area (GYA) in Wyoming, Montana and Idaho, where brucellosis is still active among elk and bison herds.
Brucellosis is caused by a strain of bacteria, Brucella abortus. It originated in cattle herds, which spread it to elk and bison. Now, the elk are returning the favor. Though bison are also affected, and there is currently a domestic bison herd with the disease in Montana, bison and cattle rarely intermingle, so bison are less of a concern than elk.
The brucella bacteria affects the reproductive tracts and causes abortions, often late in the gestation period, says Wyoming state veterinarian Dr. Jim Logan. Sometimes cows infected with brucellosis give birth to live calves, but the calves are often weak, have difficulty breathing and die within a day.
The birth or abortion process is the dangerous time for transmission, because brucellosis is spread by cattle inhaling or ingesting the bacteria from the birth fluids.
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Male animals can get the disease, but they are dead-end carriers, Logan said. The bacteria can exist outside the body for months, depending on the weather conditions. The bacteria live longest in cool, damp, shady places.
The transfer of the disease from elk to cattle most often happens when they are brought together during the elk calving season. A variety of factors can cause the elk and cattle to overlap their ranges, including weather, feed and predators.
In a section of Wyoming, Montana and Idaho, called the Designated Surveillance Area (DSA), producers are required to follow guidelines for vaccinating, and testing before moving or selling animals. The cattle in this area are considered to be at a higher risk for getting brucellosis because of the incidence of brucellosis in elk in the area.
The testing is paid for by the states, but producers do have associated costs, Logan said. "Anytime you put cattle through a chute, an expense is involved as far as shrink, risk of injury, stress. There's a price attached that's very difficulty to quantify, but it certainly exists for the producers. The extra help, time involved, it all adds up."
Logan said the best time to test for brucellosis is during preg-checking, so the cattle are already being run through the chute, and the vet just has to take a blood sample. Testing can be done at any time, though, and results are usually back within a week.
The Wyoming Department of Fish and Game has been working with hunters on testing elk for brucellosis, and this fall some elk outside the DSA have tested positive. That raises concerns for cattle producers in those areas, and for the Wyoming Department of Livestock, which is responsible for the rule-making surrounding the issue.
Logan said he will be scheduling meetings with producers in Bighorn and Sheridan counties, where the new infected elk were found. The meetings will provide information for producers about preventing the spread of brucellosis, and voluntary testing. "It's a whole lot easier to do some things to prevent the problem than to deal with it after a herd becomes infected," Logan said. At this point the WLB is not in the process of considering changing the boundaries of the DSA, but is looking at risk factors and surveillance rates for that area. "We definitely appreciate all the efforts of producers within the DSA and the efforts in Bighorn and Sheridan counties, and encourage them to continue surveillance to protect their herds from the disease."
According to the USDA-APHIS website, "The basic approach has always been to vaccinate calves, test cattle and domestic bison for infection, and send infected animals to slaughter. Depopulation of herds, if funds are available, may be used if herds are severely affected. Identification of market animals for tracing, surveillance to find infected animals, investigation of affected herds, and vaccination of replacement calves in brucellosis-affected areas are important features of the current program. "
Though the Bangs vaccination program has helped prevent brucellosis, Logan said the existing vaccines only about 70 percent effective. Experiments with vaccinating elk and bison have been less effective because of the differences between the wildlife and bovine immune systems.
Dr. Frank Galey, Dean of the College of Ag and Natural Resources at the University of Wyoming, and chair of the Wyoming brucellosis coordination team, said UW is working on improving the vaccine. Logan said there are studies going on at several locations across the country to find a better vaccine, and develop better testing for both elk and cattle. The vaccine the industry uses now, RB51 is a good vaccine, but isn't 100 percent effective. "The industry would benefit from having something that was more efficacious," Logan said.
Historically, the bangs vaccine was assumed to be part of the health protocol for replacement heifers. Montana is now taking comments on a proposal to change that.
The proposed rule would remove brucellosis vaccination requirements for cattle imported into Montana from states, provinces and territories that have been brucellosis-free for at least 10 years, according to a press release from the Montana Department of Livestock.
"While this would be a change from the way we've done things in the past, the simple fact is that 46 states have been brucellosis-free for at least 10 years or more, and there is negligible risk of importing the disease from those states," Montana state veterinarian Dr. Marty Zaluski said.
Zaluski said the proposal would benefit producers by reducing regulation and vaccination costs, and eliminating the need for upon-arrival quarantines.
"The proposed rule will not impact our efforts on brucellosis surveillance and science-based prevention in areas of known risk in southwestern Montana," Zaluski said.
The vaccination requirements for the four counties in Montana's DSA would not be changed. F