Estimated reading time: 4 minutes
Brucellosis is widely regarded as a serious threat to livestock producers in South Africa. While it may not currently command the same level of attention as issues like foot-and-mouth disease, its impact remains significant. In response, the Dairy Standard Agency (DSA) invited Dr Mark Chimes, veterinary advisor and Milk SA’s programme manager for animal health and welfare, to share his expertise on the topic during a DSA webinar.
The necessary precautions
Brucellosis poses a serious threat to dairy farms, with infected herds potentially causing significant losses. These include the compulsory slaughter of affected animals, decreased milk production, and reduced premiums, as milk buyers often lower prices for milk sourced from brucellosis-positive farms. According to Dr Chimes, it is therefore essential to take all possible measures to prevent the disease from entering one’s herd.
The primary way people contract brucellosis is through drinking unpasteurised milk from infected cows. If a farm tests positive for the disease, its milk must be boiled or pasteurised before consumption. This extends to dairy products made from raw milk, such as cheese, yoghurt, and ice cream, as brucellosis bacteria can survive in these for up to three months.
Human infection can also occur when infected material comes into contact with mucous membranes (such as the eyes or mouth) or open cuts – particularly during calving, when large quantities of the bacteria are present in birth fluids; producers and veterinarians are especially at risk during these times.
“Inhalation of airborne organisms can also cause infection. Symptoms resemble the flu and can become chronic if not properly treated,” explains Dr Chimes. “Since animal vaccines are live, it is crucial to avoid accidental needle pricks or splashback while vaccinating cattle. To prevent such incidents, always wear protective gear (gloves, a mask, safety glasses) and appropriate clothing when handling vaccines.”
Read more about the dairy regulatory landscape.
How animals are infected
Brucellosis often goes unnoticed within herds. It is not classified as a sexually transmitted disease, as its primary mode of transmission is oral – typically occurring when animals come into contact with birth fluids from cows that have recently calved or aborted foetuses. Once inside the animal, the organism targets the lymph nodes, where it begins to multiply. It also becomes intracellular, meaning it prevents the immune system from detecting the infection, thereby stopping the production of antibodies.
Pregnant cows produce a carbohydrate called erythritol, found in the foetal membranes within the uterus. It attracts the Brucella bacteria, making the reproductive tissues particularly susceptible to infection. When an infected cow aborts, the expelled material is heavily contaminated, spreading the disease to the surrounding environment and other animals. Predators and scavenging birds can further transmit the infection by dragging contaminated tissue across farms.
Calves born to infected cows may carry the disease but often test negative, as their immune systems struggle to detect this highly intracellular pathogen. They are also at risk of becoming infected by consuming milk from infected mothers.
“The key issue is that heifers infected with brucellosis typically do not test positive until after they have calved or aborted,” explains Dr Chimes. “Testing too soon after birth may yield false negative results. Producers should therefore wait at least a month before conducting blood tests for antibodies. This delay is one reason why it is vital to separate newly purchased heifers from the main herd until they’ve tested negative at least twice after calving. It’s also essential to obtain heifers only from farms certified as brucellosis-free.”
Economic consequences
In herds with no prior exposure to brucellosis, the disease often appears as a sudden and significant increase in the number of abortions, or abortion storm, in which up to 30 to 40% of calves may be lost. These abortions typically occur in the last trimester of pregnancy, although embryonic death can also happen during the early stages. Brucellosis has serious reproductive consequences: it can lead to uterine inflammation and reduce conception rates, lowers calving rates, and extends inter-calving periods. As a result, multiple insemination attempts may be required to achieve pregnancy, increasing costs.
Brucellosis can also decrease milk production due to its association with mastitis. Infected bulls may also suffer from testicular infections, negatively affecting their fertility.
Prevention and management
To prevent brucellosis from spreading in a herd, the most crucial step is vaccinating one’s animals. This creates herd immunity, reducing the likelihood of infection. “The only way to eliminate this disease,” says Dr Chimes, “is through testing and culling all animals that test positive.”
He shared some guidelines to help prevent the spread of the disease:
- Vaccinate the herd against brucellosis.
- Promptly bury or burn aborted foetuses and afterbirth to minimise the presence of infectious organisms on the farm.
- Mark areas where a cow has aborted or calved with a visible flag, and thoroughly disinfect these zones.
- Be mindful of the environment – cool, moist, or muddy conditions are ideal for brucellosis bacteria to thrive.
- Disinfect all equipment that came into contact with infected cows. – Carin Venter, Stockfarm
For more information, contact The Dairy Standard Agency on 012 665 4250, or send an email to jacqueline@dairystandard.co.za or info@dairystandard.co.za.
