Brucellosis

BRUCELLOSIS

Brucellosis is a bacterial infection of domestic animals and human caused by 4 species of Brucella. These are B. abortus, B. melitensis, B. ovis and B. suis. Brucellosis in cattle is mainly caused by B. abortus, but can occasionally be caused by B. suis and B. melitensis when cattle are in contact with pigs or small ruminants. Infections with B. abortus are usually symptomless, except in pregnant cattle which cause abortion from seventh months onwards. Aborted cattle discharge large number of B. abortus bacteria in the placenta, foetus and vaginal discharges. These are the main sources of infection to other animals. B. abortus bacteria can usually survive for several weeks outside the host. Other animals can become infected by ingestion and sniffing of contaminated material. Once an animal has aborted, it may remain infected and discharge large number of organisms when giving normal births. Calves can be infected in the womb before birth, but these calfhood infections usually disappear before puberty. The organisms can also be excreted in milk which is a common source of infection to human. Because aborting and calving cows are the major source of infection, Brucellosis is a very serious disease in dairy industries. hen brucellosis is suspected, the animal should be isolated from the rest of the herd or flock. Aborted materials should be put in a plastic bag and sent for laboratory tests. Any contaminated materials should be burned or buried, and the location where the abortion occurred should be thoroughly cleaned with disinfectant. Controlling the disease involves a combination of management, hygiene and use of appropriate vaccines.

Clinical signs:

Brucella infections are usually symptomless, except in pregnant females which cause abortion from seven months onwards. Subcutaneous swellings containing infected fluid are quite common on the legs in African cattle. A thickened leathery is usually appeared in the placenta with necrosis of the cotyledons. B. abortus infection in bulls may cause orchitis.

Treatment:

There is no effective treatment for brucella infections. In most cases, treatment is not attempted as it is neither practical nor economically viable.

Control measures:

Controlling brucellosis involves a combination of management, hygiene and the use of vaccines. In a herd with known history of brucellosis, any cows about to calve should be isolated. Any suspicious cases should be separated from the rest of the herd. Aborted foetuses and foetal membranes should be tied in a plastic bag and sent for laboratory tests. The location where the abortion occurred should be disinfected and any contaminated materials should be burned or buried.

Vaccination is an effective method to prevent brucellosis infection. Calves up to the age of eight months can be vaccinated with a live vaccine based on a B. abortus strain. This vaccine will confer life-long immunity. In older animals, this live vaccine has to be used with care because it can cause abortion in females and orchitis in bulls. A dead B. abortus vaccine is also available to use for adult animals, but requires a repeated vaccination every year.

The most effective way to control brucellosis is to slaughter the infected animals which can be detected by various diagnostic techniques. However, this method is expensive and requires a high level of management. In eradication programmes, vaccines can be used to reduce the disease level, followed by slaughter the infected animals to eliminate the disease.

WWW Sites of Relevance

Arnot Ogden Medical Center

World Organisation for Animal Health

Livestock Conservation Institute

World Organisation for Animal Health