Brucellosis

Brucellosis is a family of infectious and contagious gram negative coccobacilli (Brucella abortus, melitensis, ovis ,suis, canis) that causes disease in animals and humans. It is one of approximately 80 diseases that can be transmitted from animal to humans (zoonoses). The disease primarily effects cattle and bison although it has been reported in sheep, goats, pigs, horses, dogs (and wild canids), wild ungulates (elk, deer, caribou and reindeer) and humans. Because of it’s large economic impacts on American animal agriculture (estimated loss of $800 million annually if there was not an eradication program) and possible human health implications, an eradication program was begun in 1951. Visit the USDA Brucellosis site material we downloaded to read about brucellosis. In particular view the Brucellosis Survelance information to see the current status of the disease in the US . Think about what you can conclude on the location and likely origin of the disease in the cattle over the last 5 years. You may get a clue from the the additional resources but it requires you know something of geography and federal lands in the affected areas. If you can not figure this out, look at a map of where these states come together and look at what is there.

While cattle, sheep and pigs are the major farm species infected by this disease, wild animals are also effected leading to emotional controversies around national parks. Approximately 40% of the elk wintering at Jackson Hole, WY test positive for the disease (3600 elk). Ranchers around Yellowstone National Park (Greater Yellowstone Area), accuse the bison of spreading the disease to the cattle herds adjoining the park. How this controversy of killing animals coming out of the park border will play out is uncertain (USDA Veterinary Service: Cattle and Bison). More recent infections in cattle seem to be mostly of Elk origin. An unidentified brucella has been found in Arctic seals and other marine mammals. The etiology of this strain remains uncertain.

Cause

In cattle, brucellosis is generally identified by late term abortions and inflammatory lesion in the male reproductive tract. The bacteria are an intracellular pathogen that survives and replicates in the white blood cells. In the female, the organism localizes in the udder, uterus and lymph nodes adjacent to the reproductive tract causing degeneration of the placenta leading to abortion or the birth of weak calves. In bulls, the organism localized in the testicles. Transmission is most often through ingestion although there are reports of venereal transmission.

The table below summarizes Brucella strains, hosts and transmission mode.

Diagnosis

The microorganism can be identified bacteriologically, by direct culture of the microorganism from infected tissues in selective medium, or direct stained smears. Commonly, diagnosis is made serologically, by tests as serum tube agglutination test (SAT), and milk ring test (suspect animal serum or milk is tested for the presence of specific anti-brucella antibodies.

Treatment and Control

There is no treatment for Brucellosis in animals. It is controlled by official vaccination and entire herd testing with slaughter of reactors. Quarantines are imposed by state and federal authorities until the herd is proven free of disease. Animals are also blood tested at slaughter and positive reactors traced back to the farm of origin. Vaccines have used different strains of brucella for creation, such as RB-51, so animals vaccinated can be differentiated from naturally infected animal. However human infection from the the 2 different vaccines used in 2016 has occurred, most likely by accidental needle sticks. Other routes of human infection are contact with infected animals, be it livestock or wildlife such as elk or pigs, or eating undercooked meat from infected animals. Current areas of the world most at risk for humans includes the Mediterranean Basin likely due to brucellosis in sheep and consuming unpasteurized sheep milk products. Only North America is relatively free due to vigulance of the USDA.

Treatment in humans includes long term antibiotic therapy with some individuals never fully recovering.

If a cattle herd is located in an area of brucellosis infection, vaccination of heifers between 4-10 months of age is indicated. Calves born to vaccinated cows will acquire circulating antibody titers from colostrum, which will last 4-6 months.

Brucella were one of the first organisms weaponized by the US government in the 1950's but stocks were destroyed in the early 1970's.

Other Links

CDC information on Brucellosis and Humans
Canine Brucellosis - Wisconsin Department of Health (use this link for canine first)
Canine Brucellosis - Colorado PDF