Elk brucellosis rates rise in Cody area
by Wyoming Game and Fish Department
March 15, 2009
Elevated brucellosis rates recently found in elk from the Cody area have wildlife experts rethinking the link between high rates of brucellosis and elk feedgrounds. There are no elk feedgrounds in the Cody area.
The Wyoming Game and Fish Department has been collecting data to measure the prevalence of brucellosis in Wyoming elk for more than 25 years. Until now, there has been a clear link showing higher prevalence rates in those elk that are annually congregated on winter feedgrounds in northwest Wyoming. In other areas of the state, the disease historically has been either non-existent or present at very low levels in free-ranging elk.
On April 30, 2007, an aborted elk fetus, a tell-tale sign of the disease, was found on a ranch southwest of Cody. The fetus indeed tested positive for brucellosis. This finding reaffirmed the Game and Fish Departmentís interest in more closely monitoring elk in the Cody area to get a better picture of how prevalent the disease is there. The best way to do so is to provide hunters with a blood sampling kit and ask them to collect blood as they are field dressing their animal.
Brucellosis has been present in elk in the Cody area for years at relatively low levels. Samples taken from hunter-killed elk in the area since 1991 indicate that seroprevalence rates (the percent of elk that have been exposed to the disease) in the area has been around 3 percent. However, data collected over the past three years has shown seroprevalence rates at approximately 10 percent.
"Hunters have been pretty good about getting us blood samples," said Wyoming Game and Fish Wildlife Disease Specialist Hank Edwards. "We received 232 usable samples from this past hunting season, which is a respectable sample size, so we appreciate everyoneís effort." Blood samples also were gathered as part of an elk research project being conducted north of Cody.
Wyoming Game and Fish Wildlife Veterinarian Terry Kreeger agrees that the data are worth paying attention to. "In three years of sampling the results have consistently shown a seroprevalence of around 10 percent," says Kreeger. "We have to believe itís real." Both Edwards and Kreeger believe these results warrant further testing.
The significance of these findings lies in the fact that elk in the Cody area do not attend winter feedgrounds as they do in the Jackson and Pinedale regions, where brucellosis has had a stronghold for many years. Seroprevalence rates among feedground elk have ranged between 8 and 50 percent, with an average of around 30 percent over the years.
"This finding kind of flies in the face of the traditional dogma that says brucellosis is a feedground disease," says Kreeger. "Clearly, concentrating animals on a feedground is not good from a disease standpoint, but this is showing us that you do not have to have a feedground setting to perpetuate brucellosis."
Kreeger noted that while there are other areas in the state with fairly large wintering concentrations of elk, elevated brucellosis rates have not been detected anywhere else to date. Brucellosis is known to exist in both bison and elk in Yellowstone National Park.
It is believed that the disease is most commonly spread when an animal aborts its calf and other nearby animals visit the fetus, either sniffing or licking it. "It may just be that one aborted fetus amongst a large concentration of animals can be enough to perpetuate this disease, whether itís on a feedground or not," said Kreeger.
Wyoming Game and Fish officials plan to continue their sampling efforts in the Cody area as well as other locations around the state. "I canít say enough, how appreciative we are to those hunters who take the time to get us their blood samples," said Edwards. "We know itís a bit of an inconvenience, but the data are extremely valuable to the management of the stateís wildlife."