Brucellosis: A threat to livestock and humans

Nicole Schwandt
2d
3 min read

Brucella is a group of bacteria that can infect both animals and humans, primarily affecting the reproductive systems of animals and causing longstanding flu-like symptoms in people. Different species target specific animals: B. abortus in cattle, B. melitensis in goats and sheep, B. suis in pigs, and B. canis in dogs.

For this article we will focus on Brucella abortus, a serious disease that leads to significant economic losses in cattle herds and poses a health risk to humans.

Impact on cattle

Brucellosis primarily affects cattle by causing abortions, stillbirths, retained placentas, and reduced milk production. Infected animals excrete the bacteria through aborted foetuses, placenta, and milk, increasing the risk of disease spread. Some infected cattle may appear healthy, complicating disease identification and control.

Transmission to humans

As a zoonotic disease, brucellosis can be transmitted from animals to humans. Human infection typically occurs through direct contact with infected materials such as aborted foetuses or placentas, or by consuming unpasteurized milk and dairy products from infected animals. In humans, the disease can cause serious complications, including fever, joint pain, and, in some cases, chronic health issues.

Disease spread among cattle

Brucellosis is a herd disease; if one animal is infected, the entire herd is potentially at risk.
Pregnant heifers and cows infected with brucellosis may abort and become temporarily infertile, leading to extended calving intervals and decreased production.
Infected cows and heifers typically abort only once and may appear healthy, which is misleading. These animals can continue to spread the infection through the placenta and milk, causing significant financial and production losses.
The primary mode of transmission is when an infected animal gives birth or aborts, releasing millions of bacteria into the environment, easily infecting other animals and humans.
Heifers born to infected cows often test negative until their first calving. Therefore, they should be kept separate from the herd until they have calved and tested negative for brucellosis.
Brucella bacteria in infected materials (aborted foetuses and placentas) can be further spread by stray dogs, jackals, and crows. Flies feeding on infected materials can mechanically transmit the bacteria when they land on the nasal mucous membranes of animals.

Government's role

Under the Animal Diseases Act, Act 1 of 2011, Brucellosis is a notifiable animal disease.
A notifiable animal disease means that any positive cases must be reported to the Directorate of Veterinary Services (DVS), specifically the Chief Veterinary Officer (CVO). Veterinarians play a role when blood samples test positive in a laboratory.
The DVS's role in managing a notifiable animal disease includes monitoring, prevention, and control. They are responsible for monitoring outbreaks and developing and implementing public health policies.

Vaccination

By law, all heifer calves between the ages of 3-8 months must be vaccinated once with a registered vaccine (S19). If the S19 vaccine is administered at an older age, the animal may continuously test positive in blood tests, causing confusion about its disease status.
Non-pregnant heifers can be vaccinated with the RB51 vaccine, and cows can be vaccinated at any time, as it does not result in positive blood test results. Heifers or cows should be vaccinated twice with RB51: the first dose between 4-10 months of age, followed by a booster at 12-16 months. Only non-pregnant female animals should be vaccinated.
Vaccination helps protect your herd against the disease and prevents its spread and the number of abortions.
Do not vaccinate bulls with the S19 or RB51 vaccines, as it can render them sterile.
Owners are responsible for the health of their animals and can be prosecuted under the Animal Diseases Act if they contribute to the spread of Brucellosis.
It is important to insist on information about animals' origins and vaccination records when making purchases. Proof of negative herd test results should be provided if available. For biosecurity reasons, it is always advisable to keep cattle being added to the herd in isolation, test them for various diseases, vaccinate them, and treat them for internal and external parasites.