BRUCELLOSIS HISTORY AND BIOLOGY
Brucellosis is a highly contagious bacterial disease of both animals and humans that has been recognized since the nineteenth century. A cooperative state-federal brucellosis eradication program has existed for more than seventy years because of the disease’s economic impact on cattle ranchers and because it can be a serious human disease. This program has nearly eliminated brucellosis in domestic livestock, but the disease still exists in free-ranging elk and bison in the greater Yellowstone area, including northwest Wyoming. Brucellosis is not found in wildlife anywhere else in the state.
Brucellosis was probably introduced into the Yellowstone area from infected bison that were transplanted into Yellowstone National Park from a brucellosis-infected cattle ranch. In addition, elk likely contracted brucellosis when they shared feed with infected cattle in and near Yellowstone in the early 1900s.
There are several species of the Brucella bacterium; Brucella abortus is the species that infects elk, bison, and cattle. The current taxonomic scheme recognizes eight strains: B. abortus types 1 and 4 are probably the most common isolates from elk and bison in the greater Yellowstone area.
Brucellosis Infection of the female reproductive tract results in abortion. A cow usually aborts her first calf following infection; a few cows will abort their second, or even third, calves as well. Fetuses delivered near term often are stillborn or fail to thrive due to overwhelming Brucella infection. The male reproductive tract (testes, seminal vesicles, prostate) can also be infected. Infection of the bone or joint membranes results in lameness that may make the animal more susceptible to predation.
The most common route of transmission is thought to be oral. Elk, bison, and most other ungulates lick newborn young, whether the youngster is alive or dead, and whether it is one of their own offspring or not. They often eat placentas, fetal sacs, and even stillborn young. This instinctive reaction to a birth gives Brucella a perfect avenue for infecting new animals. Licking or eating an infected fetus or placenta, licking the vulva of an infected female that has just given birth, consuming any of the fluids that leave an infected female at birth— any of these is enough to transmit brucellosis to another animal.
Under cool, moist conditions, Brucella bacteria can survive for more than 100 days in the environment. An elk or bison that consumes feed or water contaminated by vaginal discharges or fetal membranes may develop brucellosis. Treatment of the disease in wild animals is difficult because it requires multiple drugs administered daily for several weeks.
The Wyoming Game and Fish Department tests elk for brucellosis at many of its feedgrounds. It also gathers blood samples from elk that are thought not to winter regularly on feedgrounds— these samples are taken from elk killed by hunters. The Wyoming Livestock Board and the USDA Animal and Plant Health Inspection Service regularly test cattle throughout the state.
Blood testing shows the proportion of animals that have been exposed to brucellosis and developed antibodies— veterinarians call this proportion “seroprevalence.” This testing doesn't necessarily mean that the animal can transmit the disease. Another test is used to culture the bacteria from tissue samples— a positive case or "culture positive," indicates that the animal actually harbors the bacteria and may be able to transmit to other animals.
Managing brucellosis in elk, wild bison, and cattle in the greater Yellowstone area is one of the most complicated and contentious wildlife management issues in North America. Often called a “political disease,” brucellosis affects both livestock and wildlife, resulting in social, economic, biological, and political complications that are a constant challenge for wildlife and livestock officials.
Many interest groups— state and federal wildlife and agricultural officials, hunters, ranchers, outfitters, conservationists, landowners, and the general public— are touched by this disease. Managing brucellosis requires a cooperative, multi-pronged approach that uses new techniques, research, and progressive thinking that are, at times, controversial.
Over the last thirty years, a coalition of government agencies, private-sector organizations, and individuals has mounted a growing effort to solve the brucellosis problem. Together, these groups have built an aggressive program of vaccination, conducted research on new vaccines, and managed land to provide better habitat for wildlife. Though Wyoming’s brucellosis problem is far from being solved, these efforts have made a significant difference in the scope and impacts of the disease. Continued research, management actions, and cooperation by all parties involved promises even more progress in the future.
Brochures and Additional Information
Brucellosis: What is UW doing?
UW seeks better brucellosis control through vaccine development, vaccination practices
College of Agriculture and Natural Resources scientists at the University of Wyoming are hopeful their brucellosis studies may produce a better vaccine for livestock and are studying whether a change in vaccination procedures could offer better control.
Brucellosis can cause elk, bison and cattle to abort fetuses. The highest risk of brucellosis transmission to other animals occurs after an animal has an abortion. The organism can also be transmitted to humans, often through consumption of unpasteurized milk or dairy products such as soft cheese, which may result in a severe disease called undulant fever.
We have eradicated the disease from livestock but occasionally get a disease spillover from elk transmitting the organism to livestock,” said Bruce Hoar, University of Wyoming brucellosis research coordinator. “One of the ways we try to control brucellosis is through the use of vaccinations.”
Scientists are interested in pursuing vaccines for wildlife, particularly elk; existing vaccines for cattle are not very effective at preventing disease in elk. The emphasis, though, is on livestock vaccines, said Hoar.
Cattle in the U.S. have been vaccinated since the 1930s with a vaccine called Strain 19. That vaccine was moderately effective preventing 60-70 percent of cattle from aborting after becoming infected, said Hoar. Strain 19 was replaced by a vaccine called RB51 in the 1990s and is the currently licensed vaccine for cattle.
“It, too, only protects 60-70 percent of animals in the herd, so that leaves 30-40 percent of the herd vulnerable, and, because of that, we are looking for better vaccines, and that is what a team of researchers here at the University of Wyoming have been involved in for a number of years,” said Hoar.
Several investigators at UW are looking at different vaccines. Gerry Andrews, associate professor in the Department of Veterinary Sciences and a medical microbiologist, has developed unique vaccines.
“These vaccines have been tested in the mouse model of brucellosis,” said Hoar. “They are in the early stages of development, but we are very excited and hopeful this will lead to a better vaccine for cattle.”
Another, more recent, effort is to simply vaccinate with more doses of RB51 vaccine, said assistant professor Jeff Adamovicz in the department.
“We recently completed a vaccine study in Black Angus cattle and have promising results that show multiple doses of RB51 vaccine reduced abortions in cattle and may also reduce the risk of transmission,” said Adamovicz. “We hope to pursue a recommendation to change the vaccination practices in Wyoming based on our findings.”
Other efforts to model the risk of brucellosis transmission and development of economically feasible ranching practices are also of interest.
These efforts parallel vaccine development efforts but are an important part of the overall goal of reducing transmission and economic impacts to Wyoming ranchers, according to Brant Schumaker, an assistant professor in the Department of Veterinary Sciences, and Dannele Peck, associate professor in the Department Agricultural and Applied Economics, at UW.
Other on-going efforts to break disease transmission are also important, said Hoar. These include the work of the Wyoming Game and Fish Department, a crucial partner in the effort to control the disease, he said. Elk calves on the feeding grounds are still vaccinated with Strain 19.
Game and fish department personnel are able to vaccinate the elk with a “bio bullet,” which contains a freeze-dried vaccine pellet. The bullet is shot into a rear muscle of the animal and then breaks down, slowly releasing the vaccine into the animal. That technique works well but in a non-feeding ground elk population, the process becomes more challenging, said Hoar.
In northwestern Wyoming, 20-40 percent of elk will test positive on a blood test, which means they were at some point exposed to the bacterium. That doesn’t necessarily mean they are actively spreading the organism, said Hoar.
As one goes east of Yellowstone National Park into Park County, 5-15 percent of elk can be seropositive, which shows they have been exposed to the disease and that brucellosis has spread farther east. Most recently, seropositive elk have been found in Big Horn County raising concerns about the spread to local cattle, although no seropositive cattle have been found in this area, said Hoar.
“It is still a concern, because we are seeing it where we historically haven’t been seeing it in our elk,” said Hoar.
The most recent farm bill approved use of funds for brucellosis vaccine research.
“There could be significant funding for brucellosis vaccine research, and that would be a really good thing,” said Hoar. “The University of Wyoming would be a great competitor for these grant funds, as we already have a well-qualified team in place that can perform the research. Our long-term goal is to develop vaccines, vaccine strategies and diagnostic tests that will enhance our ability to control the potentially devastating effects that this disease could cause to Wyoming cattle and wildlife.”
Credit: University of Wyoming College of Agriculture and Natural Resources.
Hunters Urged To Help With Brucellosis Research
LARAMIE – Not only is there a call out to give blood these days, there’s also a request for hunters to take blood.
Nearly 6,000 antlerless elk license holders in the Cody, Lander and Cokeville areas will be receiving kits to take a blood sample from their quarry. The sample will be tested to check the range and prevalence of brucellosis in elk. Brucellosis is a bacterial disease, which can induce abortions in elk, bison and cattle.
Wyoming Game and Fish Department Disease Specialist Hank Edwards said the blood sampling done by hunters is a very important part of the state’s long-running brucellosis monitoring program.
Edwards said instructions are included with each kit and hunters should follow the guidelines carefully to ensure the samples are usable. “Timely collection of the blood and then getting the sample in the mail to the laboratory as quickly as possible is very important,” he said. “Hunters should also try to keep the sample from freezing.”
Only about half of the hunters receiving kits harvest an elk and send the samples back to the lab, and of those, only half are usable. “The more viable samples we get, the better information we have on the status of the disease,” Edwards said.
Since 1991, over 7,300 elk blood samples have been analyzed in Wyoming for brucellosis. To date, the disease has only been documented in western Wyoming, with prevalence levels of 1 to 3 percent in the southern herd units surrounding feedgrounds, and from 9 to 10 percent in the corresponding northern herd units, around Dubois, Meeteetse and Cody.
“The northern units have been of great interest over the past several years, where the historical prevalence was similar to the southern herd units, but for unknown reasons the incidence of this disease has dramatically increased,” Edwards said.
Game and Fish personnel will also be collecting blood samples in the field this season from hunter-harvested elk in the Wheatland and Douglas areas.
BRUCELLOSIS IN CATTLE
Frequently Asked Questions
What is brucellosis?
Brucellosis in cattle, elk, and bison is a disease that is caused by a bacterium, Brucella abortus. This is also known as contagious abortion or Bang’s disease. Swine and reindeer can be infected with another species, Brucella suis, while Brucella melitensis can infect goats. In humans, infection with any of these bacterial species can result in a disease called undulant fever.
How important is brucellosis?
Brucellosis is an important disease of livestock and an important zoonosis (disease transmitted from animals to people) worldwide. It is of major economic importance to livestock industries in developing countries that do not have national eradication or prevention programs, as it can result in decreased milk production, weight loss, loss of young, infertility, and lameness. There are also significant trade implications associated with infection. The fact that the disease can spread rapidly and be transmitted to humans further emphasize its importance.
What are the signs of brucellosis, and how is it spread?
Animals infected with brucellosis usually do not show any outward signs of illness. The most obvious signs in pregnant animals are abortion or birth of weak calves. Milk production may be reduced, there may be a reduction in fertility with poor conception rates, retained afterbirths and occasionally enlarged, arthritic joints. Not all infected cows abort, but those that do usually lose their pregnancy between the fifth and seventh month of pregnancy. After abortion or birth, the bacteria persist in low numbers and “hide” in an animal’s tissues until the next pregnancy, when massive growth in bacterial numbers and seeding of the bacteria in large numbers in fetal tissues and fluids occurs. Therefore, the disease is most easily transmitted from animal to animal during abortion or birthing. A percentage of infected cows will abort during subsequent pregnancies. Calves born from infected cows may have latent infections, that is, infections that are not detected until they become pregnant, abort, or give birth.
Aborted fetuses and fetal membranes and uterine secretions eliminated after abortion or calving are the most important sources of infection. Grazing on infected pasture, or consuming other feedstuffs and water supplies contaminated by discharges and fetal membranes from infected cows, and contact with aborted fetuses and infected newborn calves are the most common methods of spread. The bacteria can survive in the environment for variable periods, depending on the conditions. In temperate climates, infectivity may remain for 100 days in winter and 30 days in summer. The disease can also be transmitted to calves while in the uterus and through contaminated milk, but these routes are much less important.
The direct impact of brucellosis on wildlife populations appears to be modest. Wyoming Game and Fish Department has estimated that about 7% of elk calves are aborted by younger elk cows on their first calving season following infection. Older cows are at less risk of aborting, although if infected they will still shed the organism at birthing.
Clinical symptoms in human brucellosis include recurring fever, loss of appetite, arthritis in multiple joints, meningitis, pneumonia, heart infections, and other less common clinical manifestations. In most cases, human infection is due to consumption of contaminated non-pasteurized milk and cheese or as an occupational exposure to infected animals or carcasses, uterine secretions or aborted fetuses (e.g. farmers/ranchers and veterinarians). Less often accidental infection may occur due to manipulation of live vaccine strains or Brucella in the laboratory. As human brucellosis is essentially a zoonotic disease, control and prevention of brucellosis in animals is essential for eradicating the disease in man.
Can brucellosis in animals be cured?
No. Despite numerous attempts to develop effective therapies, the fact that the bacteria are intracellular pathogens (live inside cells of lymph nodes, mammary gland, and reproductive organs) make it very difficult to achieve clearance of the bacteria from the body. Occasionally, animals may recover after a prolonged period of time, but more commonly, only the signs disappear and the animal remains infected. Such animals remain as potential sources of infection for other animals they contact.
Is there a vaccine for brucellosis?
Yes, the vaccine is a live product called RB51, and must be administered by an accredited veterinarian or State or Federal animal health official. The vaccine typically protects about 70% of the vaccinated animals from becoming infected. Female calves are vaccinated one time between 4 and 12 months of age. When they are vaccinated, heifers are also tattooed in the ear, which identifies them as “official vaccinates”. Properly vaccinated cattle are less likely to be infected and less likely to abort if they do become infected. Current vaccines are even less effective in elk and bison.
What about wildlife, specifically bison and elk?
Brucellosis is considered to be endemic (widespread and common) in elk and wild bison in the Greater Yellowstone Area (GSA). It is estimated that the Jackson Bison Herd has a brucellosis prevalence of 50 to 80% and may be considered a reservoir for contamination for other species. Elk on winter feedgrounds in the GYA have an average seroprevalence of exposure of about 30%. Elk that winter off feed grounds on less densely populated wintering ranges in the GYA have significantly lower prevalence. Previous cases of brucellosis in cattle herds have been linked to infection in elk.
What is currently being done about brucellosis in Wyoming?
Multiple strategies are currently being employed to help reduce the threat of brucellosis. Although imperfect, vaccination is useful in cattle and may be helpful for elk on winter feedgrounds. Heifer calves in the State are vaccinated against brucellosis using RB51 vaccine. High-risk cattle can be revaccinated as adults with permission of the United States Department of Agriculture and the State Veterinarian. Elk have been vaccinated with Strain 19 via ballistic bio-bullets by the Wyoming Game and Fish Department on most of the State elk feed grounds.
Another important strategy is to prevent commingling of elk, wild bison, and cattle during the critical periods of transmission in the late winter and spring. Elk are being fed at key areas to keep them off cattle feed lines. The duration of elk feeding is being reduced as much as possible in an effort to encourage the elk to move to summer pastures earlier in the year, thereby further limiting contact between high-risk elk and cattle. Fencing and hazing are used to move elk away from the cattle and vice- versa. Allotment use is timed on spring range conditions, but ranchers are encouraged to use caution when moving cattle near high-risk areas.
Surveillance is another important tool used by State and Federal regulators. The Wyoming Livestock Board (WLSB) has specific rules and orders addressing the requirements for moving cattle from the Designated Surveillance Area (DSA) in Wyoming. The latest version of the Chapter 2 Rules can be found at http://wlsb.state.wy.us, or call the WLSB at (307) 777-7515. Elk are trapped on selected winter elk feed grounds and tested for brucellosis. Also, blood sample kits are distributed by Wyoming Game and Fish Department to a proportion of purchasers of elk hunting licenses in targeted regions of the State. The hunters are encouraged to submit a blood sample if they successfully harvest an elk, thereby adding another layer of surveillance for the State. Bison testing is not done as routinely as elk testing in Wyoming, but is practiced adjacent to Yellowstone National Park on animals migrating west and north into Montana.
What does brucellosis in humans look like?
People infected with Brucella can have a range of signs and symptoms, some of which may present for prolonged periods of time (years or a lifetime). Initial symptoms can include fever, sweats, chills, loss of appetite, headache, fatigue, and pain in muscles, joints and back. Long term effects can include arthritis, chronic fatigue, recurrent fevers, depression, and swelling of internal organs. Treatment may require several weeks to several months of antibiotic therapy.
How are humans usually infected?
The most common way to be infected is by eating or drinking unpasteurized or raw dairy products from infected animals. Bacteria can also enter wounds in the skin or mucous membranes through contact with infected animals. This poses concern for workers who have close contact with animals or animal excretions, such as slaughterhouse workers, veterinarians, and farmers/ranchers.
How can people reduce the risk of contracting brucellosis?
People who handle animal tissues, such as hunters and animal caretakers, should protect themselves by wearing sturdy rubber or plastic gloves when field dressing and handling tissues from wildlife, assisting calving or aborting animals, and scrub well with soap and water afterward. Do not consume unpasteurized dairy products, including milk, cheese, and ice cream. Ultimately, the best prevention is to eliminate brucellosis from all animals in the area.
For further information on human brucellosis, visit the Centers for Disease Control and Prevention website at: CDC - Home - Brucellosis
WYOMING BRUCELLOSIS COORDINATION TEAM
In 2004, Wyoming Governor Dave Freudenthal created the Wyoming Brucellosis Coordination Team to chart a course for brucellosis management in the future. The team presented the governor with 28 recommendations for actions to help manage and control the disease in elk, wild bison, and cattle. Today, many of those actions are being implemented, and the combined efforts of agencies, landowners, and others are bringing measurable success in the battle against this stubborn disease.
Francis D. Galey, University of Wyoming College of Agriculture
Joel Bousman, Rancher, Sublette County Commissioner
Jose Castro, USDA Forest Service
Jessica Crowder, Governor Mead’s representative
Fred Emerich, WY State Senator
Andrea Erickson, The Nature Conservancy
Marty Griffith, US Bureau of Land Management
Michael Healy, WY Game and Fish Commission
Rob Hendry, Rancher, Natrona County Commissioner
James Kaste, Attorney General Representative
John Keck, National Park Service
Will Laegreid, WY State Diagnostic Laboratory
Bill Lambert, Rancher
Jim Logan, Wyoming Livestock Board, State Veterinarian
Shawn Madden, Madden Brothers Livestock Yard
Mike McDole, USDA Animal and Plant Health Inspection Service
Bob Meyer, Wyoming Livestock Board, Assistant State Veterinarian
Doug Miyamoto, WY Department of Agriculture
Karl Musgrave, Department of Health Services, Public Health Veterinarian
Terry Pollard, WY Outfitters and Guides Association
Charles Price, WY Game and Fish Commission
Albert Sommers, WY House of Representatives
Scott Talbott, WY Game and Fish Director
Joe Thomas, Rancher, WY Livestock Board
Scott Werbelow, WY Game and Fish Department
Bob Wharff, Sportsmen for Fish and Wildlife
Bill Williams, Veterinarian and former WGFD Commissioner
Mary Wood, WY Game and Fish Veterinarian
2005 Team Report and Recommendations
Wyoming Brucellosis Coordination Team
Minutes from previous meetings
- WY State Vet Report 2018
- Montana 2018
- Idaho 2018
- Non-feedground Elk 2018
- Bighorns update 2018
- Feedground Elk 2018
- WY State Vet Report
- MT Report
- Idaho Update
- WGFD Brucellosis Surveillance
- North Bighorn Elk Movement
- NER Step-Down Plan Update
- RB51 Vaccine
- WY state vet report
- 2015 BCT MT update
- Schumaker Hull Spring 2015 BCT Presentation
- 2014 Brucellosis Elk Survey
- Yih_BCT meeting
- WBCT Letter
- 2012 North Bighorn Sero-Positive Tests in Elk
- Economic Performance of Converting From a Cow/Calf/Yearling System to a Stocker/Yearling Operation as a Response to Brucellosis
- Brucellosis Situation in Kenya
- 2012 Brucellosis Surveillance in Hunter-Killed Elk
- Brucellosis in Uganda: Experiences with the Disease
- Phase out elk feedgrounds: Gros Ventre Pilot Project
- Accidental Exposure to Cattle Brucellosis Vaccines in Wyoming, Montana, and Idaho Veterinarians
- Status of Brucellosis in United Republic Of Tanzania