Where bovine brucellosis was relatively under control in South Africa around the nineteen-eighties, there has been a steady increase in cases of this bacterial disease over the past ten years. Lax biosecurity measures and failure to vaccinate seem to be the main drivers behind these outbreaks. Glenneis Kriel reports.
There has been a rising incidence of bovine brucellosis cases in almost all the provinces of South Africa over the past ten years. But not only bovine brucellosis (Brucella abortus), there has also been an increase in Brucella ovis, which primarily affects sheep, as well as a few incidents of Brucella melitensis, which causes Malta fever in humans.
While there has been past reports that about 10 per cent of the national dairy herd might be affected, Dr Willem Schultheiss, manager of the ruminant division of Ceva in South Africa, believes the percentage might be lower.
“There is a strong awareness of bovine brucellosis in commercial dairies, because these farmers are required by law to test their animals with State veterinarians reporting the herd status. Cases on emerging dairy farms, in contrast, might be under reported as not necessarily all cattle are tested in remote areas,” Dr Schultheiss said.
Dr Sewellyn Davey, a State Veterinarian and coordinator of Bovine Brucellosis in South Africa, estimated that the percentage of beef cattle affected by the disease, could be significantly higher than the percentage in dairy cattle, because beef farmers are not required to do routine tests for the disease. Beef cattle were in general also a side-line on many farms with the animals being produced under extensive production conditions.
Quantifying losses is also difficult. Dr Schultheiss explained that the disease could have a negative impact on farm bottom lines in different ways. Positive animals, first of all, had to be slaughtered by law resulting in a loss of breeding material.
The disease however also affected herd efficiency, by resulting in abortions or by causing cows to take longer to reconceive. Calves that are not aborted and survive, usually never catch up with the rest of the herd.
Cattle also sometimes don’t exhibit any symptoms, except for a 10 per cent to 20 per cent decline in milk production. “This makes it difficult for farmers to identify the disease, as milk production might still be in the ‘normal’ range in spite of the disease,” Dr Schultheiss explained.
Dr Schultheiss said that one of the problems with the management of brucellosis, was that it was treated on a “need to know” basis with most private veterinarians and beef farmers preferring not to disclose an outbreak publically.
“Brucellosis these days has become stigmatised like leprosy in the Bible’s time. Instead of informing others of the lurking danger, farmers prefer to keep quiet. Surrounding farmers, as a result, are unable to take timeous measures to protect their herds and enhance their biosecurity measures to prevent the disease from spreading,” he said.
There is also a reluctance to report cases, even though it is required by law, because it would result in the farm being placed under quarantine. Farmers in effect are not allowed to trade or move animals from the herd, unless with a special permit to slaughter animals.
Affected beef cattle also have to be destroyed, whereas dairy cows might be allowed to finish a lactation if the majority of the cows in the herd is affected. This however is on condition that no infected cow may calve down on the farm as this is when infection is spread.
According to Dr Davey, movement restrictions are only lifted once the disease is completely eradicated and cattle have undergone a series of negative tests taking the incubation period of the disease into account.
She said that the movement of animals is one of the biggest causes of the spreading of the disease: “Farmers seem to be unaware of the risk and they buy cattle from unknown sources or unknown status. Animals should be tested for the disease before they are moved onto a new farm and they should be kept separately from other animals until it is certain they are not affected. Failure to do this has resulted in the disease spreading to regions where it has never been a problem before.”
Dr Schultheiss added that auctions were especially a problem, as animals with unknown Brucellosis status from different farms are presented at the auction increasing the risk of the spread of the disease. State veterinarians have the authority to demand that animals are tested shortly prior to an auction, but this isn’t always possible and not always well received.
One of the difficulties in controlling the disease, according to Dr Davey, was that farmers were no longer vaccinating their animals against the disease so the bovine population is naive to the disease.
“Government used to offer this service for free around the nineteen-eighties resulting in the national prevalence of the disease dropping to 1,5 per cent between 1985 and 1987. Farmers however had to buy their own vaccine from 1991 and heifer vaccination dropped dramatically since then.”
To address this issue, government and industry has been holding various workshops to make farmers more aware of the problem.
Dr Schultheiss believes the workshops are having an effect as he estimated that the number of animals that are being vaccinated against the disease has increased from less than 15 per cent in 2013 to more than 30 per cent now. Estimating the number of animals that are vaccinated is however difficult, as some cattle are vaccinated more than once.
According to the Brucellosis Scheme of 1988 calves should be vaccinated between four and eight months with an effective remedy. A single vaccination however only protects about 65-75 per cent of vaccinated cattle against the risk of abortion. So it is preferable to re-vaccinate heifers before artificial insemination or putting a heifer to the bull, especially in regions with a high prevalence of the disease. For vaccination to have an impact on the disease, more than 80 per cent of the national herd would need to be vaccinated, and even more to completely eradicate it, according to Dr Schultheiss.
Another challenge was that farmers tended to shift the responsibility of control to Government. Dr Davey said that there are very sound policies in place to prevent the disease from breaking out and to eradicate the disease. Government however didn’t have the resources to police and enforce these policies.
“Farmers should take responsibility for biosecurity on their farms and industry could also play a significant role,” she said.
For more information contact Dr Sewellyn Davey at firstname.lastname@example.org