Brucellosis: The Disease

[Snowden]

BRUCELLOSIS: THE DISEASE



Brucellosis in cattle and bison is a serious chronic bacterial infection caused by the bacterium Brucella abortus. Brucellosis causes cattle and bison to abort their fetuses. In humans, an infection of B. abortus, B. suis, or B. melitensis causes undulent fever. (Hagan, 1957)

B. abortus is especially virulent because is can survive within cells of the host organism, even macrophages. Inside the host's cells, B. abortus is protected from antibodies and antibiotics in the blood. There are several vaccines for brucellosis in cattle, including a low-virulence, live vaccine derived from B. abortus strain 19. No current vaccine is completely effective. (Hagan, 1957)

B. abortus is spread from bison to bison or from cow to cow (there have been no documented cases of interspecial transmission) by contact with an infected pregnant female, or ingestion of infected milk, an infected aborted calf, or infected afterbirth (placenta and other birthing materials). B. abortus invades through mucus membranes, can enter and survive absorption by phagocytes, and spread to various organs, including the liver, spleen, bone marrow, kidney, and uterus. When the infection reaches the uterus, the placenta can be infected, causing inflammation and ulceration of the membranes, leading to the abortion of the fetus. After the abortion, the infection remains in the Iymphatic system and can contaminate the infected organism's milk for life. (Hagan, 1957)

Undulent fever is a disease caused by an infection of B. abortus in humans. It can have an incubation period as long as weeks or months. Undulent fever is very difficult to diagnose because it has vague and differing symptoms, including chills, fever, sweats, weakness, fatigue, psychoneurosis, myalgia, and headaches. (microvet.arizona.edu, 1998)

Undulent fever is named for the severe intermittant fever that is one of its symptoms. Undulent fever is rarely fatal. Undulent fever is usually transmitted from livestock to humans by injestion of raw milk, contact with infected fetuses, afterbirth, and uterine discharges, or contact with infected animals when they are slaughtered. Undulent fever is very rarely transmitted from human to human. Pasteurization kills the bacteria in milk, and cooking removes the bacteria from infected meat. (APHIS, 1998)



Brucellosis is a major problem for cattle ranchers in the Greater Yellowstone Area. Apart from any existing infections in their herds, cattle ranchers have to worry about infected bison from Yellowstone National Park that may come in contact with their livestock. While there has never been a documented case of bison to cattle transmission of brucellosis cattle ranchers are still concerned that their cattle could be infected. Montana cattle were granted "brucellosis-free" status in 1985, and in order to keep that status, ranchers and government officials from the National Park Service and the Montana Department of Livestock slaughter many bison that leave Yellowstone. (Popular Mechanics, 1998)

Montana's "brucellosis-free" status indicates that brucellosis has been eliminated from Montana cattle. This status earns cattle ranchers about $6 million per year, as the meat poses no threat of undulent fever to humans, and the cattle can be shipped easier since they pose no threat of brucellosis to other livestock. Montana ranchers and authorities have spent over $30 million since 1985 to maintain the status. (Fretwell and Platts, 1997)

Although the only possible threat of transmission would be from pregnant female bison, since brucellosis is transmitted by contact with or ingestion of an infected pregnant female, infected milk, a brucellosis-aborted calf, or infected afterbirth, two-thirds of the bison slaughtered in the winter of 1996 were males, calves, and females that were not pregnant. Montana ranchers are so concerned because if they find even one infected cow, they must slaughter their entire herd to protect the brucellosis-free status. This fear forces Montana authorities to slaughter bison, which pose no documented threat of infection. (Popular Mechanics, 1998)


Disease

[satin_patriot]

That's what my parents had last year. There are only about 100 cases in humans per year. It's REALLY HARD to get rid of, too. They had to have their entire immune systems shut down with antibiotics, then had to rebuild. My mom is still having lingering problems, a year later.

Ugly stuff, the brucellosis.

[Woodmonkey]

I thought that was strictly an animal disease. Learned something new.

[Snowden]

I remember when they were so ill, Lacey. I didn't realize this was what they had, though.