Brucellosis is a highly contagious, zoonotic disease caused by bacteria of the genus Brucella. There are several species of Brucella, each having slightly different host specificity. Brucella abortus most commonly affects cattle, but is also known to infect bison and elk. B. Suis is most common in swine and B. melitensis is most common in goats. Brucella species sometimes spill over and infect other animal species, including humans. B. abortus is the species of most concern to hunters and wildlife professionals in Montana (Michigan, 2010), and will be the focus of this information.

Brucellosis is found worldwide, but is most common in countries without good public and veterinary health programs. Brucella abortus was once present across the United States, but as the result of a brucellosis eradication program that began in 1935, and advances such as vaccination and pasteurization of milk, the disease has nearly been eliminated. The only known remaining focus of disease caused by B. aboruts is in the Greater Yellowstone Area.

Brucellosis caused by B. abortus is a disease of cattle that has spilled over into wildlife in some areas. Bison and elk are the primary wildlife hosts of B. abortus (Miller et al, 2003) . It has also been found in moose, Dall sheep, caribou and several species of deer, although much less commonly than in elk and bison. Additionally, infection has rarely been diagnosed in dogs, foxes, hares, mice, rats, ticks and fleas.

Brucella abortus is now being maintained in some elk and bison populations without an outside source of infection, and these populations serve as a reservoir for potential transmission of the disease to cattle. The National Brucellosis Eradication Program has nearly eliminated brucellosis from domestic livestock.

Brucellosis transmission in cattle, bison, and elk generally occurs by ingestion of bacteria, which are present in large numbers in aborted fetuses, fetal membranes, and uterine discharges. It is not unusual for cattle, elk, and bison to be curious and investigate an abortion site. Animals may ingest contaminated feed and water or may lick contaminated genitals of other animals. Venereal transmission by infected bulls to susceptible cows appears to be rare. 

Most human cases occur from consuming milk that has not been pasteurized. Hunters, veterinarians, abattoir workers, and others who handle carcasses may be exposed via contact with bacteria through mucous membranes of the eyes or mouth, skin wounds, or via inhalation.

Abortion, usually late in pregnancy, is the most obvious clinical sign of disease in cattle, elk, and bison. Usually, only the first calf is aborted after the cow has become infected. Future pregnancies often result in a live birth. Retained placentas, decreased milk production, and weak calves are also signs of brucellosis infection in these species. Infection of the bull reproductive tract can result in inflammation and abscesses. Less commonly, infection with Brucella bacteria may cause arthritis, formation of abscesses in lymph nodes, and inflammation of mammary tissue (Miller et al, 2003) . Chronic infections of bones and joints occur in livestock and reindeer, resulting in lameness and abscesses (Michigan, 2010).

Detailed information about brucellosis in humans can be found on the CDC website: https://www.cdc.gov/brucellosis/index.html. Humans may become infected through skin abrasions, mucous membranes, or the conjunctiva of the eyes during activities such as butchering or field dressing, handling fetuses or afterbirth, contact with the secretions and excretions of the genital system of an infected animal. Humans can also be infected by consuming raw milk from an infected animal, or by consuming raw or undercooked meat that has been contaminated with fluids (primarily from the reproductive tract) containing Brucella. Symptoms of Brucella abortus infection in humans include: weakness and fatigue, lack of appetite, sweating, muscle and joint pain, fever, and/or mental inattention and depression (Miller et al, 2003).

Hunters can reduce their risk of exposure during field dressing by wearing gloves and avoiding the reproductive organs of elk, which is where most of the bacteria are located. Wash hands, forearms, and instruments well with warm soapy water after handling a potentially infected animal. Reusable instruments can be cleaned with a dilute bleach solution. Although muscle tissue typically does not contain Brucella, it can be unknowingly contaminated during the field dressing process. Meat should be cooked thoroughly to a temperature of at least 165°, which would kill the bacteria if contamination occurred.

Is it safe to eat the meat?

The bacteria that cause Brucellosis are not normally found in muscle tissue and are killed by normal cooking temperatures. Meat can be safely consumed if cooked thoroughly to a temperature of at least 165° – however, freezing, smoking, drying or pickling will not kill the bacteria. Brucella bacteria may also be found in the bone marrow and liver. Meat from an infected carcass or a carcass thought to be infected should NOT be fed to domestic cats or dogs. If you harvest an animal and are unsure whether it is safe to eat, contact your local FWP staff for guidance soon after the animal is harvested.

Centers for Disease Control and Prevention. Brucellosis. Website. https://www.cdc.gov/brucellosis/index.html Accessed 1/31/22

Michigan Wildlife Disease Manual. 2010. Michigan Department of Natural Resources. Website

Miller, M.J.R., R.D. Dawson, and H. Schwantje. 2003. Manual of Common Diseases and Parasites of Wildlife in Northern British Columbia. University of Northern British Columbia.

Western Wildlife Disease Workshop Notebook. 2009. Southeastern Cooperative Wildlife Disease Study. College of Veterinary Medicine, University of Georgia.