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Brucellosis

Brucellosis

The disease in cattle, water buffalo, and bison is caused almost exclusively by Brucella abortus; however, B suis occasionally is isolated from seropositive cows but does not appear to cause clinical signs and is not contagious from cow to cow.
Infection spreads rapidly and causes many abortions in unvaccinated cattle. In a herd in which disease is endemic, an infected cow typically aborts only once after exposure; subsequent gestations and lactations appear normal. After exposure, cattle become bacteremic for a short period and develop agglutinins and other antibodies; some cattle resist infection, and a small percentage of infected cows spontaneously recover. A positive serum agglutination test usually precedes an abortion or a normal parturition but may be delayed in ~15% of cows. The incubation period may be variable and is inversely related to stage of gestation at time of exposure. Organisms are shed in milk and uterine discharges, and the cow may become temporarily infertile. Bacteria may be found in the uterus during pregnancy, uterine involution, and infrequently, for a prolonged time in the nongravid uterus. Shedding from the vagina largely disappears with the cessation of fluids after parturition.
Natural transmission occurs by ingestion of organisms, which are present in large numbers in aborted fetuses, fetal membranes, and uterine discharges. Cattle 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.

Clinical Findings

Abortion is the most obvious manifestation. Infections may also cause stillborn or weak calves, retained placentas, and reduced milk yield. Usually, general health is not impaired in uncomplicated abortions.
Seminal vesicles, ampullae, testicles, and epididymides may be infected in bulls; therefore, organisms are present in the semen. Agglutinins may be demonstrated in seminal plasma from infected bulls. Testicular abscesses may occur. Longstanding infections may result in arthritic joints in some cattle.

Diagnosis

Diagnosis is based on bacteriology or serology. B abortus can be recovered from the placenta but more conveniently in pure culture from the stomach and lungs of an aborted foetus. Most cows cease shedding organisms from the genital tract when uterine involution is complete.
VETLAB Bovine Brucella Test- ( Serum agglutination test) have been the standard diagnostic method.

Screening Tests

The RBPT has effectively located infected dairy herds. The brucellosis status of dairy herds in any area can be monitored by implementing the RBPT at 3- to 4-mo intervals as well as FOR ANY NEW ANIMAL WHICH IS BEING ADDED TO HEARD,

Brucellosis-free areas can be achieved and maintained, effectively and economically, by using the BRT on dairy herds and through market cattle testing. Adult cattle are sampled at the time of slaughter.

Control

Efforts are directed at detection and prevention, because no practical treatment is available. Eventual eradication depends on testing and eliminating reactors. The disease has been eradicated from many individual herds and areas by this method. Herds must be tested at regular intervals until two or three successive tests are negative.

Non infected herds must be protected. The greatest danger is from replacement animals. Additions should be vaccinated calves or non pregnant heifers. If pregnant or fresh cows are added, they should originate from brucellosis-free areas or herds and be seronegative. Replacements should be isolated for ~30 days and retested before being added to the herd.

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