Why brucellosis vaccination is vital
Because bovine brucellosis causes abortions, it has a severe impact on calving percentage. All livestock farmers should play their part in eradicating the disease by vaccinating their herds.
Bovine brucellosis has been identified as the single greatest threat to the red meat industry, apart from footand-mouth disease. Brucellosis is especially dangerous as it is a zoonosis, which means that humans can also become infected.
Brucellosis results in abortions in cattle, and can cause devastating losses for a farmer. The disease is chronic and, once introduced, is without cure. Farmers are therefore compelled by law to vaccinate all their heifers once between four and eight months of age with either S19 or RB51.
Brucellosis is caused by the Brucella abortus bacterium and is most commonly spread between herds by the movement of infected animals. In particular, the disease can be spread when healthy cattle lick or eat the discharge of infected animals during calving or abortion, and for one month thereafter. This can result in an acute outbreak of the disease in a herd, during which 30% to 40% of in-calf females may abort (a so-called abortion storm).
Abortions usually occur between five months’ gestation and full term. Hygroma (fluid accumulation in the knee joint) may appear in some cases.
WHAT TO DO FOLLOWING AN OUTBREAK
• Send specimens to a laboratory Specimens of the foetal abomasal fluid, lung, spleen, liver and foetal membranes should be taken from aborted foetuses. Smears should also be made of the aborting cow’s lochia and the cotyledons of the placenta. These samples should be sent to a laboratory on ice as soon as possible after abortion, with each organ packed separately in a sterile jar.
• Serological tests
Blood samples are collected by a veterinarian or a registered, authorised technician in vacuum tubes properly marked with the animal’s identification number. The samples are sent to a South African National Accreditation System laboratory for testing. A negative result immediately after abortion may be false, as the animal’s immune system might not yet have developed antibodies, so a repeat serological test after two weeks or more will provide a more reliable result.
Latent heifers are a particularly dangerous threat as they can transmit brucellosis and are carriers of the disease, but do not yet show up positive in serological tests.
• Herd test
Brucellosis diagnostics should be interpreted according to the status of the herd of origin, as brucellosis is a herd disease. A negative test result for an individual animal means nothing without the herd status. If an individual animal tests positive, however, the entire herd is seen as potentially positive and has to undergo further testing under quarantine.
Testing and retesting at herd level will also help to clarify suspicious reactions or reactions caused by late S19 vaccination.
Combating brucellosis in communal herds is a challenge as these animals are reared in a farming system where multiple owners use common pastures and watering points. The cattle effectively form a homogenous herd with similar disease status even though the various owners do not necessarily make common decisions on their animals. Compliance with heifer vaccination as prescribed in the Animal Diseases Act No. 35 of 1984 is usually poor, therefore these cattle herds tend to be susceptible to brucellosis infection when placed in contaminated communal grazing.
The public perception of brucellosis is also problematic as the disease is usually not plainly apparent, so owners find it hard to accept that their animals are affected or infected. To cull infected cattle has an undesirable impact on the social standing of the owner in the community. It is also difficult to reach consensus on whose cattle are ‘responsible’ for the disease and therefore whose animals must be slaughtered for the benefit of all.
• Visit nahf.co.za, click on ‘Info Centre’, then on Diseases.
• Phone the RPO on
012 349 1102/1103, or email [email protected]tic.net.
ABOVE: Cattle usually become infected with brucellosis by licking or eating infected afterbirth, eating infected feed or grass, or drinking infected water.