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- Brucellosis is a notifiable zoonotic disease that requires immediate reporting upon a positive laboratory result in cattle.
- An electronic survey revealed that less than 10% of beef cattle herds undergo testing for brucellosis, indicating a lack of awareness and control in the beef industry.
- In contrast, commercial dairy cattle are tested regularly, leading to fewer positive cases and quicker eradication when infections occur.
- Vaccination of heifers with the S19 Brucella vaccine is crucial for long-term protection against brucellosis, providing 85% immunity.
- Effective control of brucellosis includes stringent market access regulations, herd testing, and the culling of positive animals to prevent further spread of the disease.
Brucellosis is a notifiable disease which means that it must be reported to the state veterinarian as soon as the laboratory report for tested cattle reveals a positive result; the accredited laboratories that conducted the tests usually send the notification themselves. It is clear from Figures 1 and 2 showing the areas for which notifications had been sent in that this disease, which is also transmissible to humans (zoonotic), is running rampant.
Figure 1: Reported outbreaks of bovine brucellosis during 2023.
Figure 2: Reported outbreaks of bovine brucellosis from January 2018 to December 2022.
An electronic survey conducted in August 2024 among the veterinarians participating in the countrywide disease reporting scheme revealed that, according to most of them, very few of the beef cattle in the country undergo testing for bovine brucellosis. A total of 99 veterinarians participated. They were asked what percentage of beef producers in their practice area had tested their cattle for brucellosis (Table 1).
Table 1: Percentage of producers who had their beef cattle tested for brucellosis.
| Percentage tested | Number of producers |
|---|---|
| <10% | 51 |
| 11-20% | 21 |
| 21-50% | 15 |
| 51-75% | 6 |
| >75% | 5 |
What about the dairy industry?
The incidence of brucellosis in commercial dairy cattle differs drastically from that of the beef industry. Few dairy herds, and in some provinces none, test positive for brucellosis. While some dairy herds do test positive, quick action is taken and the infection is usually eradicated within a year. What places dairy cattle most at risk is the presence of neighbouring beef cattle farms where no testing has been done.
Market access is the main reason for the difference between the two industries. Dairy producers wishing to supply milk to milk buyers must prove that their herds are brucellosis-free by having their animals tested annually. Regular milk-ring tests allows for herd status monitoring throughout the year.
Disease control
In addition to the fact that brucellosis is a zoonosis and that infected animals are lifelong carriers of the disease, its prevalence and the risk it poses necessitate urgent control.
The most practical point of departure for curbing the spread of brucellosis is to vaccinate all heifers between the ages of four and eight months with the S19 Brucella vaccine. A single dose at this age provides 85% protection against the disease for the rest of their lives.
The testing of herds and slaughtering of positive animals at Red Cross abattoirs are surefire ways of eradicating the disease.
Limiting market access is the most effective method of controlling it in the medium to short term. Auction facilities and abattoirs will require a declaration stating that herds have undergone testing and are free from brucellosis before these animals are offloaded.
Biosecurity and traceability
Given the most recent outbreaks of foot-and-mouth disease in the south of the country, the implementation of a traceability system for cattle has become a reality. This will include bovine brucellosis, being one of the specified diseases that can benefit from better control through market access regulation and monitoring of animal movement from one farm or region to the next.
Therefore, a drastic change will be seen over time in terms of brucellosis control in a bid to stop it from running rampant. A basic overview of the disease can serve as a reference.
Organism
The bacterium Brucella abortus causes brucellosis. Note that this is an intracellular organism; if the organism is already present in the cells, the body’s immune system will have trouble fighting it, and antibiotics will not be as effective.
Transmission
Direct transmission takes place when susceptible animals come into contact with the excreta – especially abortus, afterbirth, and amniotic fluid – of an infected animal. Pathogens are ingested orally when susceptible animals lick infected material; the pathogen can also gain access through the respiratory tract and mucous membranes such as those of the eyes.
Development
During initial infection the pathogen spreads through the body slowly, settling in the uterus and udder tissue of cows, or the testicles of bulls. Hormonal changes in the cow/heifer activate the pathogens, prompting them to divide as soon as the animal is in-calf, and the udder tissue starts to develop prior to lactation. The pathogen causes an infection in the area where the placenta attaches to the uterus, which leads to the animal aborting.
Except for abortions, no other disease signs can be observed. The only exception is swelling of the joints of long-infected cattle (hygroma of mostly the knee joint in the front legs). Cows that have aborted once will usually calve normally afterwards; however, the organism will still be present in the afterbirth and amniotic fluid.
Outcome
Visible signs of disease in cattle are virtually none. However, infected cattle will remain lifelong carriers of the disease. Testing the animals’ blood for antibodies is the only means of identifying animals that are infected and therefore also carriers of the disease.
It is crucial to identify and cull such animals to rid the herd of bovine brucellosis. When a herd tests positive (one or more animals are positive), the entire herd is considered positive, and no live animals may be sold for breeding purposes.
Vaccine
Heifers must be vaccinated with the S19 vaccine after four but before eight months of age so as to eliminate the chances of a false positive result when they are tested for the first time prior to and post calving. Timing is crucial seeing as heifers must be vaccinated before they are sexually mature. A dedicated syringe must be used during the vaccination process.
In herds that are at a high risk of contracting bovine brucellosis, an RB51 booster vaccine can be administered to heifers and non-pregnant cows – this vaccine increases disease protection to above 85%, but does not interfere with the tests to determine whether the herd is clean.
The vaccine only protects 85 to 90% of female animals against infection, but it does prevent almost 100% of abortions, which is the main transmission route of the disease. This largely limits transmission, should the disease enter the herd or is already present.
Treatment and prevention
There is no practical or cost-effective treatment for cattle already infected with brucellosis or animals that are lifelong carriers.
If the herd is bovine brucellosis free, everything possible must be done to avoid exposure to carrier animals. Combined with the vaccination of all heifers, this is the only method of preventing transmission and contamination. Never buy in animals that are part of a herd that tested positive.
Contact the author on 073 672 1272 or email vnet@absamail.co.za for more information.
