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Still Anxious About Brucellosis?

The announcement on May 26 by the Canadian Food Inspection Agency (CFIA) that it had launched a brucellosis investigation on two farms in southern British Columbia nettled an industry already besieged by challenges. Three beef cows from adjacent ranches in the Osoyoos area were classified as “reactors” on brucellosis tests conducted during routine slaughter surveillance in a U. S. slaughter plant. The glow of Canada’s brucellosis-free status since 1989 was momentarily tarnished.

The United States Department of Agriculture’s imposition of a temporary import restriction on all sexually intact cattle and bison in B. C. since March 25 sent a shudder through an industry still in recovery stage from the serious trade implications of other reportable diseases. The USDA’s blunt response on the strength of brucellosis screening tests was considered premature, but highlights the prominence brucellosis still occupies in the psyche of nations trading in livestock.

As expected, a host of confirmatory tests conducted by the USDA National Veterinary Services Laboratory and the World Organization for Animal Health (OIE) reference laboratory for brucellosis in Ottawa showed that initial tests on blood samples turned out to be cross-reactions to other bacteria unrelated to those causing brucellosis. Investigation of the herds in question and herd tests conducted as part of the investigation confirmed the false alarm.

The disease

Brucellosis is a chronic and contagious disease caused by several species of bacteria called Brucella. Bovine brucellosis, caused primarily by B. abortus, affects cattle, bison and elk. Caprine/ovine brucellosis, caused by B. melitensus primarily affects goats and sheep.

Humans can become infected by all types of brucellosis, including a fourth type, which is known as “rangiferine” brucellosis in northern Canadian reindeer and caribou caused by Brucella Suis Biotype 4.

Bison and elk are significant reservoirs of B. abortus. Bison in and around Wood Buffalo National Park are the only known wildlife reservoir of brucellosis in Canada. In the U. S., B. abortus infection in bison and elk in the Greater Yellowstone Area persists. The lingering presence of brucellosis in free-ranging wildlife and the potential threat it poses to domestic livestock remains a point of contention between federal, provincial/state authorities and the livestock industry on both sides of the border.

Brucellosis is a serious disease in humans and the primary reason it remains a regulated and reportable disease in most countries.

Few countries escaped the wrath of brucellosis in domestic livestock. Australia, Canada, New Zealand and Western Europe have eradicated brucellosis from their domestic herds. The United States is working toward eradication.

Others are not so lucky. China for example still considers brucellosis a serious human health threat in many livestock-producing regions. In 2007, nearly 20,000 cases of human brucellosis were reported. In Eastern Europe and Eurasia, B. melitensis infection has re-emerged as a serious threat in sheep and goats. B. melitensis is very contagious for humans.

Canada initiated an eradication program for bovine brucellosis in livestock in the 1940s, and was declared free of the disease in 1985. Several isolated cases of bovine brucellosis in livestock were subsequently identifi ed, with the last known case occurring in a cattle herd in Saskatchewan in 1989.

Animals become infected with brucellosis by direct contact with infected tissues or fluids from infected animals, through consumption of colostrum and milk from infected animals and through feed or water contaminated by infected tissues.

Clinical signs

Following infection in animals, Brucella spread through the blood and lymphatics. Many tissues are invaded — particularly the reproductive organs, mammary glands and joints.

The main clinical signs in cattle are abortions. Most animals abort during the first pregnancy following infection, and will carry subsequent pregnancies to term. However, they remain carriers for life, and continue to shed large quantities of bacteria during subsequent births and during lactation. Infected animals often carry brucellosis for life.

Brucella cause a disease in humans called “undulant fever,” a chronic and debilitating disease. Obstetrical procedures and Brucella Strain 19 vaccine accidents made brucellosis an occupational risk for many veterinarians and livestock producers.

Brucellosis freedom

Canada protects its brucellosis-free status through import controls, surveillance programs with investigations of all suspect cases and mandatory slaughter of all infected and exposed animals.

Surveillance programs cover cattle, swine and farmed bison, elk and deer. National herd surveys are periodically conducted through randomly selected samples at slaughter. Surveys are augmented by testing of cattle at auction markets in northern Alberta and northeastern British Columbia, due to the presence of brucellosis in free-ranging bison in and around Wood Buffalo National Park.

Canada in keeping with the OIE International Animal Health Code on brucellosis has maintained brucellosis as a notifiable disease, has demonstrated the rate of brucellosis infection does not exceed 0.2 per cent of the cattle herd. Appropriate surveillance programs have been established, and no animal has been vaccinated against bovine brucellosis for at least three years. Finally, all reactors are slaughtered and all animals introduced into Canada come only from herds officially free from bovine brucellosis.



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About the author


Dr. Ron Clarke

Dr. Ron Clarke prepares this column on behalf of the Western Canadian Association of Bovine Practitioners. Suggestions for future articles can be sent to Canadian Cattlemen ([email protected]) or WCABP ([email protected]).



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