Volume 3, Number 37 - December 11, 2003
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Transmission from wildlife
Brucellosis was eradicated from Wyoming's livestock herds by 1980, but since then there have been several outbreaks, all of which have been associated with transmission from wildlife and all of which occurred in the western portion of the state.
According to the 1997 federal review of Wyoming's brucellosis program, recent cases of brucellosis in Wyoming cattle include:
• In 1982, a cattle herd near Bondurant was found to be infected with brucellosis after two cows on the ranch aborted their calves in March. According to the federal review team, "A definite source of infection was never proven, but considering there was no other infection in the area and there was commingling with elk, wildlife was considered the most probable source."
• In 1983, a cattle herd near Cora was found affected. The Black Butte elk feedground lies within the outer borders of the ranch. The federal team noted, "No source of infection could be found other than diseased elk."
• In 1984, seven cattle in a Jackson herd were found infected with the disease, with no source of infection found other than the elk and bison that migrated extensively through the ranch.
• In 1985, a Lincoln County dairy herd was found to be affected, although all neighboring herds were found to be free of the disease. Elk reportedly were known to frequent the property and feed with the dairy cattle.
Wyoming was granted its brucellosis-free status by the federal government in 1985, and since then, only one further brucellosis outbreak has been documented.
In 1989, the Parker Land and Cattle Company of Dubois was found infected with the disease. The resulting court case found: "The court concludes that the Parker brucellosis outbreak was most likely caused by contact with infected elk or bison as those are the only two known sources of the disease in the entire state of Wyoming ...".
Although Wyoming's cattle have remained free from the disease, with the exception of the wildlife transmission cases just discussed, at least two horses have been diagnosed with the disease. One of the horses had been kept on an elk feedground in western Wyoming.
The Wyoming Game and Fish Department has long acknowledged the dire economic consequences to the state's livestock industry that could come from transmission of brucellosis from elk.
Feeding elk during the winter on feedgrounds allows the support of large elk populations and keeps the elk from damaging haystacks on private property, but it also concentrates the animals, allowing the free-flow of disease. Elk associated with feedgrounds have much higher brucellosis seroprevalance rates than those not associated with feedgrounds. To combat this problem, the state wildlife agency began an active elk vaccination program in 1985.
The state manages 22 elk feedgrounds in western Wyoming, one of which is located adjacent to Doc Jensen's ranch near Boulder. Jensen's cattle were determined to be infected with brucellosis last week.
About 550 head of elk are typically fed on the Muddy Creek feedground, according to WG&F Pinedale biologist Dean Clause. The last time the elk herd at Muddy Creek was tested for brucellosis was in 1997, when the seroprevalence rate of the tested animals was determined to be 29 percent. Clause emphasized that seroprevalence and infection are not the same thing. Seroprevalence means that the animal has tested positive for exposure to brucellosis, but doesn't indicate if the animal is currently infected with the disease.
"Infection rates, we do know, are lower than the seroprevalence rates," Clause said.
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