Farmer's Weekly (South Africa)
How to manage brucellosis on your farm – tips from top vets
A widespread problem in sub-Saharan Africa, bovine brucellosis can cripple a cattle or dairy farming operation. As no cure is available, all infected animals are required by law to be slaughtered. This makes prevention and control of the disease a crucial
Bovine brucellosis, also known as contagious abortion, is reported across all nine provinces of South Africa, particularly in the central and Highveld regions. The disease causes abortion in cattle, resulting in severe reproduction and production losses and drastically reducing financial turnover. It can infect most other mammals, including humans.
Symptoms are often vague and may resemble other diseases. Frequent testing of the herd is imperative to ensure that an outbreak is detected as early as possible.
Dr Peter Oberem, CEO of Afrivet, says that because the state veterinary services’ rigorous tuberculosis and brucellosis control programmes were halted, the true extent of the disease is unknown.
“It can, however, be clearly stated that the situation is bad and a threat to food security, food safety and human health. Fortunately […], probably all the milk sold via the major dairies and chain stores is pasteurised and/or UHT, and hence safe for human consumption.”
cause and spread
Bovine brucellosis is caused by the Brucella abortus bacterium, and is highly contagious. Cattle usually get the disease from contaminated feed or water, or after licking an infected afterbirth, calf or cow. Infected animals remain carriers of the disease for the rest of their lives. Brucellosis is a statecontrolled disease, and positive animals must be reported to the state vet immediately.
Dr Faffa Malan, manager of the Ruminant Veterinary Association of South Africa, stresses that a single infected animal can rapidly infect the rest of the herd if not identified and slaughtered before calving.
He warns that if an animal has recently been bought into the herd from an auction or another herd without the CA3 declaration as proof that the herd of origin was recently tested for bovine brucellosis, the animal could be positive or latently positive.
identifying brucellosis
Oberem says the first visible sign that a herd is infected with brucellosis will be the number of abortions.
“If these are not obvious, a lengthened intercalving period in any herd should raise concern that there’s brucellosis. Also, if the abortus is not seen, a retained placenta hanging from the vulva for more than 12 hours after the cow has calved may be an indicator of something wrong, possibly due to brucellosis. In chronic cases, hygromas [fluid-filled swellings] occur mainly on the carpal joints.”
He adds that it is not easy to detect early infection in a herd simply from clinical signs, and testing is therefore crucial.
“If abortions occur, many exposed cattle and humans will become infected, so it’s important to regularly test any herd of cattle, especially dairy cattle.
“If a stock owner suspects brucellosis in a herd, it’s critical that the attending veterinarian be consulted urgently. Because brucellosis is listed by the Animal Diseases Act of 1984 as a notifiable disease, the testing must be done under the instruction of the nearest state vet. Blood and/or milk samples will be sent to Onderstepoort Veterinary Research for testing. Most other state laboratories don’t comply with SANAS [accreditaton] standards.”
Oberem says that if a herd tests positive for brucellosis, the
state will assume full control and place it under quarantine.
“Positive animals are branded accordingly. This means that no animal, whether it’s positive or untested, may leave the property unless it’s in a sealed truck to an approved abattoir under a Red Cross permit issued by the state vet.”
He adds that removing brucellosis-negative cattle from an infected herd is highly risky, even under optimal conditions.
“The incubation period of brucellosis can vary from two weeks to a year or even longer, so a brucellosis-negative animal could become positive much later. If brucellosis-negative animals from a brucellosis-positive herd need to be transported, the group must be isolated from the herd and have two negative test results before relocation.
“Branded brucellosis-positive cattle may only leave the farm to be transported to the abattoir for slaughter. It’s wise to check whether or not the abattoir will accept brucellosispositive animals for slaughter.”
Testing positive
A herd is diagnosed positive if Brucella organisms have been isolated in birth canal tissue, placenta and lymph glands. Once brucellosis has been diagnosed, all the animals in the herd must be quarantined and placed under official oversight.
According to Malan, the first step is to cull infected, positive animals.
“There’s no silver bullet solution for brucellosis eradication. Getting back to brucellosis-free status involves repeat testing, culling and isolation.”
The following steps should be taken if your herd tests positive for brucellosis:
• Inform the local state vet.
• Once the results are attained, brand all the cows that reacted positively with a ‘C’ on the right side of the neck. • Quarantine the herd.
• Inform neighbouring farmers so they can start testing immediately.
• Do not sell any animals.
As a result of of the long and variable incubation period of the disease, no animal in a positive herd, even if it tests negative, should be sold until the farm has been certified disease-free, and the quarantine lifted. • Vaccinate all heifers between four months and eight months old with Strain 19 (S19) or RB51. Vaccinate negative, open cows (cows from eight months onwards that are not in calf) with RB51. • Monitor and continually observe brucellosispositive herds, as well as those that are suspect.
Once the positive animals have been culled, the remaining animals must be tested every two months, until three consecutive tests show negative results.
After a further six months, the herd must be tested again. It can be declared brucellosisfree or confirmed free (CF) if all heifer calves from infected cows are culled at this stage.
Failing this, the herd must be tested 12 months later
(this would be the fifth test showing negative results).
As no treatment is available for brucellosis, all positive animals must be slaughtered to ensure they are removed as a source of infection for the remaining herd, says Oberem.
“This also reduces the chances of human exposure. Culling is followed by repeated testing, slaughter of positive animals, and the creation of a geographically separate positive herd.”
Culling • Immediate cull
Cull brucellosis-positive animals as soon as possible. This is the only way to eradicate brucellosis and stop it from spreading.
Quarantined brucellosispositive cattle are allowed to be transported to only one destination: an abattoir for immediate slaughter. They may not be taken anywhere else. The receiving abattoir must make sure that the animal’s identity matches the information on the permit.
• Deferred cull
The immediate slaughter of a large number of positive reactors can disrupt farming operations, seriously affect milk supply, and ultimately cripple a farmer financially. Delayed culling may therefore be allowed, with the proviso that the milk of infected animals, or of suspected infected animals, be pasteurised or subjected to heat treatment prior to human consumption, and not sold or distributed as raw milk. This may be allowed if, for example, valuable animals, such as high milk producers, were reactors, or if the rate of infected animals was as high as 20% to 30%. Cows in peak lactation or cows with young calves at foot would also qualify for delayed culling.
Culling may also be deferred if isolated brucellosis-positive animals are branded with the required ‘C’ so that they can be identified immediately if they break out of the quarantine area.
• Timing of the cull
The cow must be culled at the end of its current lactation or when the calf is weaned, which would not be longer than 12 months.
Delayed culling gives the farmer time to plan how to handle the crisis while maintaining some cash flow by selling milk to processors. A brucellosis-positive cow is not allowed to reconceive due to the danger of transmission.
To ensure that their operation remains brucellosis-free, stock owners should ensure that the biosecurity measures in their herds and on their properties are up to standard, says Oberem.
“This means that the property should be well fenced and no animals that have not been tested and shown to be Brucellafree should be allowed onto the property. This must be very strictly implemented. The herd, or at least a representative sample thereof, should then be tested regularly.
“Vaccination should also be practised to prevent any infection should there be any biosecurity breach.
“Another really important part of the biosecurity programme should be worker training to ensure that everyone on the farm knows the risks and warning signs.”
• Phone Afrivet on 012 817 9060, or email Dr Peter Oberem at peter.oberem@afrivet.co.za.