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