UW and WGFD Seek to Unravel Elk Brucellosis Mystery
June 8, 2009 — By Rachel Knutson, University of Wyoming journalism graduate
June 8, 2009 -- Finally free, the elk sprints full speed from the holding pen. Suddenly, a few hundred yards from the corral, she abruptly stops. Turning her head, she slowly looks back wide-eyed at her capturers. For a brief second the two very different creatures are caught in a silent exchange. Then, with the realization she is not being pursued, the cow elk marches away triumphantly, head held high, no longer looking back.
"One of the most significant memories of the research is watching the elk that do not test positive run to rejoin their herd," said Todd Cornish, an associate professor in the University of Wyoming College of Agriculture's Department of Veterinary Sciences.
Cornish and Laura Meadows, who is working on a master's degree in animal and veterinary sciences at UW, are involved in a cooperative project with the Wyoming Game and Fish Department (WGFD), the goal of which is to decrease the seroprevalence of brucellosis in Wyoming's feed-ground elk.
"The term seroprevalence is used to indicate the number of animals that tested positive on a series of blood tests. This method gives us a statistically significant estimate of the number of brucellosis cases in the population," said Meadows, who grew up in Wilson, which is near several of the feed grounds in northwestern Wyoming.
Brucellosis infects reproductive organs and associated tissues, typically causing pregnant animals to abort their fetuses. The disease occasionally is transmitted from feed-ground elk to cattle when the cattle are exposed to the aborted fetus or amniotic fluids of a brucellosis-positive elk. The problem occurs when elk calving locations overlap with cattle grazing areas.
When two or more herds of cattle in a state are infected with brucellosis, the state loses its brucellosis-free status. In 2004, one cattle herd in Sublette County and another in Teton became infected, and Wyoming was no longer declared brucellosis free.
If the brucellosis-free status is lost, other states can choose not to accept your cattle, said Mark Gocke, WGFD public information specialist in Jackson. Because milk is pasteurized, brucellosis is rarely transferred from cattle to humans. Regardless, losing the brucellosis-free label can be very detrimental to a state's cattle marketing efforts, he said.
"What drives the whole elk brucellosis issue is the risk of transmission to cattle. Obviously Wyoming is a cattle-producing state, and we place great emphasis on the marketing of cattle," Gocke said.
In 2005, the Wyoming Governor's Brucellosis Coordination Team, which College of Agriculture Dean Frank Galey chairs, released a report with 28 recommendations to help prevent the state from losing its status again.
Included was a suggestion to implement a test-and-slaughter pilot program. The program requires blood to be drawn from elk on designated feed grounds in western Wyoming. Because the blood tests cannot show for certain an animal has brucellosis, the researchers must take an educated guess based on their knowledge of the bacterium and the disease. The elk that have blood test results showing likely contact with brucellosis are slaughtered in order to perform further tests at the Wyoming State Veterinary Laboratory (WSVL) in Laramie, which is managed by the UW Department of Veterinary Sciences, and the WGFD's Wildlife Disease Laboratory (WDL), which is in the WSVL.
"We are asking the question: Will test and slaughter reduce seroprevalence over time by removing positive animals?" Gocke said.
And this is exactly the question Meadows, Cornish and the WGFD are working to answer.
The test-and-slaughter study is being conducted on three feed grounds southeast of Pinedale: Fall Creek, Scab Creek and Muddy Creek. The five-year study, which concludes next winter, is taking place in the northwest part of the state, said Gocke, because this is where brucellosis generally occurs.
"Round traps are set-up on feed grounds with good hay and alfalfa to lure the elk in. There are doors on both sides that are narrow enough to prevent bulls from entering the traps," said Meadows, who stretches her hands out beside her head indicating large antlers.
Teams then count the number of captured elk, a seemingly easy task when temperatures are balmy but an arduous one when the thermometer reads 10, 20 or even 30 below zero.
"Up to 200 elk can be in the trap at once. We sort them into chutes with five elk per chute, then into individual squeeze chutes for testing. The elk become skittish easily so we try to work quickly," continued Meadows, who is familiar with this process as she has been involved in the study for four years.
Once inside the individual squeeze chute, Meadows and WGFD personnel take a blood sample from each cow or yearling, give the animals neck collars with identity numbers and an ear tag, and return the female elk to the holding pen. The calves are ear tagged and released.
"The trap itself is as easy on the elk as possible," Meadows said.
Next, the blood samples are sent to the WSVL and WDL for testing. This is when the waiting game begins in the field.
But at the WSVL and WDL, the work of Hank Edwards is anything but a waiting game. The blood must be processed and tested very quickly so the elk that do not test positive for brucellosis can be released as soon as possible.
"It is a hurried atmosphere when the samples arrive, but things slow down as the testing proceeds for the next four or five hours," said Edwards, a WGFD wildlife disease specialist who has been working on the test-and-slaughter project for four years and studying brucellosis for 15.
Each sample is put through three preliminary screening tests. If the results are positive in any of these tests, the sample proceeds through two additional tests.
"It is not cut and dry by any stretch of the imagination," Edwards said. "Brucellosis can be a wretched disease in terms of diagnostics."
Many of the tests adopted by the U.S. government in the 1930s and'40s are still being used today, he said, because a more accurate method has not yet been developed.
Throughout the procedures, Edwards is not looking for the Brucella abortus bacterium, which causes brucellosis. Instead, he is looking for antibodies against the bacterium, which signify the animal has been exposed to brucellosis. A greater number of antibodies indicate a greater chance the animal was exposed. Thus, Edwards' team cannot say for certain the animal has the disease but only has been exposed to brucellosis.
"Hank has to take an educated guess as to which ones are actually infected," Gocke said.
Meadows added, "The blood tests are the only way to estimate the prevalence in a minimally-invasive, ante-mortem way."
To determine if an elk is in fact brucellosis positive, tissue samples must be taken for culture tests. Therefore, those animals that are likely infected must be slaughtered.
"This is the crux of the problem," Meadows said. "If we are too conservative with the antibody cut-off levels, we may leave animals in the field that could continue to transfer the disease, but if we are too liberal, we are unnecessarily removing too many elk."
While there is no certain range of antibodies that guarantees an animal will be culture positive, Meadows does believe the study is bringing the researchers closer to being able to determine accurate cut-off levels.
Back in the field, the results from the lab arrive early in the morning. The elk that test negative for brucellosis are released from the holding pen in an awe-inducing manner the team sees first hand.
During the 2008-09 winter, 7 percent of elk tested at Muddy Creek feed ground showed positive signs of seroprevelence, 7 percent at Fall Creek and 20.8 percent at Scab Creek.
When asked why Scab Creek's percentage was so much higher, Meadows responded, "This is the million dollar question!"
She said seroprevalence can vary widely from year to year. On one particular feed ground, which has been tested consistently since 1993, seroprevalence has varied from 0 to 59 percent.
In addition, Meadows said, the average seroprevalence of feed-ground elk is about 23.6 percent, so Scab Creek is right about at the average. It is also difficult to compare feed grounds because they are all a little different. Other factors, such as elk density on the feed ground, elevation and size of the feed ground may need to be taken into account, she said.
That being said, there is another possibility for the difference at Scab Creek, Meadows speculated. The team has been trapping and slaughtering positives at Muddy Creek for four years now and at Fall Creek for two in an attempt to reduce seroprevalence. The 2008-09 winter was the first for testing at Scab Creek.
"The goal of this program is to achieve a statistically significant reduction in seroprevalence. So we are trying to determine if the seroprevalence at these feed grounds is decreasing as a result of the test-and-slaughter program or from numerous other factors," Meadows said.
The animals that do show seroprevalence are sent to a slaughter plant in Idaho. Meadows, Cornish and WGFD wildlife veterinarian Cynthia Tate accompany them.
"It is an interesting experience moving from the cool, quiet, open air of Wyoming where it often reaches below zero to the hot, steamy slaughter plant where they play loud music all daybut it gives you a real appreciation of how slaughter plants work," Cornish said.
At the slaughter plant, Cornish and Meadow are also acutely aware of the dangers of their work.
"We are collecting tissues most likely to be infected at a time of year when they harbor the most bacteria," Meadows said. "But the 'gear' we are using and safe laboratory practices combine to provide a good barrier for Brucella abortus transmission."
Despite the dangerous and often unpleasant conditions involved in the research, Meadows does not lose sight of her greater goal.
"In all research involving wildlife, we have to appreciate and respect those animals that are utilized in order to answer questions for the greater good of the species or managing the disease. As part of that respect, we need to strive to gather as much information as possible and to design research projects that effectively utilize each animal."
At the slaughter plant, Meadows and Cornish collect the reproductive organs and tissue samples to bring back to the WSVL and WDL to perform culture data and statistical analysis. The remainder of the elk meat is donated to schools or families in need in Wyoming. The meat is not affected by the B. abortus bacterium because brucellosis only infects the reproductive organs of an animal.
Meadows compares culture data with blood test results to draw closer to determining the antibody cut-off levels. She said the ultimate goal is to have a better understanding of these tests and the disease in elk.
"We have an unmatched sample size compared to any other elk brucellosis research so that allows us to confer positive results," said Meadows as she watched a cow elk leap to freedom.
Laura Meadows releases a calf elk from a trap at a western Wyoming feed ground after the animal was checked and fitted with an ear tag. (Photo by Dave Edmunds)
Posted on Monday, June 08, 2009