D443 - Brucella abortus

Brucellosis is a contagious, infectious, and communicable disease caused by bacteria of genus Brucella abortus. Brucellosis is the most widespread zoonosis transmitted from animals (cattle, sheep, goats, bison, and buffalo) by direct contact with blood placenta, fetuses or uterine secretions or through consumption of infected and raw animal products (especially milk and milk products). In most countries brucellosis is a notifiable disease. Overall brucellosis has an important worldwide impact on animal industries and human health. In cattle, brucellosis is primarily a disease of the female, the cow. Bulls can be infected but they do not readily spread the disease. The brucellosis organism localizes in the testicles of the bull and produces an orchitis (inflammation of the testicles), whereas in the female the organism localizes in the udder, uterus, and lymph nodes adjacent to the uterus. The infected cows exhibit symptoms that may include abortion during the last third of pregnancy, retained afterbirth, and weak calves at birth. Infected cows usually abort only once. Subsequent calves may be born weak or healthy/normal. Some infected cows will not exhibit any clinical symptoms of the disease and give birth to normal calves. The brucellosis organism is shed by the millions in fluids associated with calving and aborting. The disease is spread when cattle ingest contaminated forages or lick calves or aborted fetuses from infected cattle. Outside the animal, the brucella bacteria are easily killed by sunlight, high temperatures and drying; however, the brucella organisms are difficult to control while they are in the animal; there is no economical cure for a brucellosis infected animal.

Once the acute period of brucellosis disease is over, animals may present with little or no disease symptoms, and Brucella cells can chronically be located in the supramammary lymphatic nodes and mammary glands of 80% of infected animals; thus, animals continue to secrete the pathogen in their body fluids. The diagnosis of brucellosis is currently based on serological and microbiological tests. It is well known that serological methods are not always sensitive or specific. Moreover, they have repeatedly been reported to cross-react with antigens other than those from Brucella spp. Also, current serological tests cannot predict whether an animal is actively infected. Microbiological isolation and identfication are the most reliable methods of diagnosing fro brucellosis. However, these procedures are not always successful, are cumbersome, and represent a great risk of infection for laboratory technicians. Furthermore, since these microorganisms can be spread by aerosol routes, additional biological containment measures must be added to control the risk of infection. Fortunately, new DNA-based diagnostic testing procedures circumvent the problems associated with traditional methods of detection. Because DNA-based tests detect the actual DNA of Brucella abortus, rather then detecting an antibody response to infection, none of the problems associated with serological testing apply. Using the PCR (Polymerase chain reaction), unique genetic sequences exclusive to Brucella abortus can be detected with superior specificity and sensitivity, ensuring veterinarians and livestock owners a definitive and rapid method of diagnosis for Brucella abortus.