In 2014 there was the much-hyped case in the UK where two women contracted bovine TB from their cat, which in turn was infected by badgers, prolific carriers of BTB. They, in turn, had been infected via an outbreak of bovine TB among cows on the outskirts of the town.
The UK government launched a controversial programme whereby 26 000 cattle and some 1 800 badgers were culled in an effort to stem the tide of BTB in the UK.
Could this happen in South Africa?
Dr Nikki le Roex, a molecular biologist with Stellenbosch University’s Faculty of Medicine and Health Sciences (FMHS), says that, unlike TB in humans, which is mostly confined to the developing world, bovine TV (BTB) is a worldwide problem.
Dr Le Roex says that in South Africa BTB not only threatens the wildlife and farming industries, but may also be transmitted to humans that consume infected animal products.
“This is particularly concerning in areas with a high HIV prevalence, as people with HIV are at a much higher risk of contracting TB,” she says.
Although the African buffalo is the species most commonly affected by BTB in South Africa, it has also been detected in baboons, leopards, cheetah, impala, kudu, warthogs and lions.
“The existence of BTB in our country could result in major economic, ecological and public health impacts, on other wildlife species as well as the surrounding livestock and farming communities,” says Le Roex.
In cattle and African buffalo, BTB is transmitted between members of a herd through inhalation (breathing, coughing and sneezing) and infection may cause weight loss, fever, coughing and a general decline in health. Predators become infected either by eating infected prey or through transmission during prey capture.
Buffalo may develop lung lesions, but their symptoms are less pronounced or absent, while other species, such as lions, become very ill and may even die.
“Lions can be severely and fatally infected by BTB, and as a key predator species this may have consequences for the ecosystem,” says Le Roex.
In an effort to address the issue of BTB, researchers at Stellenbosch University are looking at why some buffalo become infected with BTB, while others in the same herd don’t. For this they are examining the DNA of individual animals to determine whether their genetic makeup play a role in whether the animal is resistant or susceptible to the disease. Based on this they could find and select animals that are more resistant to the disease.
Image: a buffalo is sedated ahead of testing for BTB
Health24's Q&A with Dr Nikki le Roex
Which other countries (other than SA) are affected by bovine TB?
BTB has affected every continent in the world at some time – it has been suggested that BTB was transported across the world via infected cattle during the colonial expansions of the United Kingdom and the Netherlands.
Other countries that have known wildlife maintenance hosts of BTB include New Zealand (brushtail possum), the United Kingdom (Eurasian badger), the United States (white-tailed deer) and Spain (European wild boar).
What is the scope of bovine TB in SA? (ie, how widespread is it, do you have any figures or numbers of infected animals?)
The scope of BTB in South Africa is difficult to quantify. Information on the status of BTB infection in cattle is not publicly available.
In terms of wildlife, African buffalo were considered the single wildlife maintenance host of BTB for some time, but there is now evidence to suggest that this role may also be fulfilled by other species, such as kudu. As wildlife are not routinely caught and immobilised, BTB testing is primarily done on an ad-hoc basis when there is evidence to suggest BTB infection, or infection is discovered during necropsy.
In the case of most species, however, diagnostic tests have never been developed. Both the Kruger National Park and Hluhluwe iMfolozi Park have BTB in buffalo at prevalence levels of between 10-55%, depending on the herd and region within each park.How are animals tested for BTB, and is this routinely done?
Image: Dr Nikki le Roex in her laboratory at Stellenbosch University’s Faculty of Medicine and Health Sciences (FMHS)
In which part of SA would you find the highest concentrations of animals infected with BTB?
In buffalo, the highest published prevalence estimates in South Africa come from Hluhluwe iMfolozi Park, where certain regions have shown prevalence estimates of up to 55%.
How are animals tested for BTB, and is this routinely done?
In cattle, BTB testing is performed using the single comparative intradermal tuberculin (SCIT) test, which is a skin test similar to the TB test given to people. In buffalo, this is also the most commonly utilised test. Variations of this test have been tried in other wildlife species, to varying degrees of success.
The regularity of BTB testing in buffalo depends on the disease management system of the different parks – for example, Hluhluwe iMfolozi Park runs an annual BTB testing scheme, while the Kruger National Park conducts surveillance as deemed necessary.
What is the difference between human TB and bovine TB? Which one is deadlier to humans?
The difference between human TB and bovine TB is that they are caused by two different but very closely related bacteria, one of which has evolved to primarily infect humans (Mycobacterium tuberculosis), and the other has evolved to primarily infect animals (Mycobacterium bovis).
People are unlikely to become infected with bovine TB except in particular circumstances, such as if they are immune-compromised by another disease (e.g. HIV). If a person does become infected with bovine TB, it can have equally devastating consequences as human TB.
Can we ‘catch’ TB from live animals who carry bovine TB? I refer to a case in England last year where people got infected with TB via their cats.
As shown by the case of TB transmission from cats, people can become infected by animals with BTB. The drinking of unpasteurised milk from cattle is considered to be the most likely route of infection here in South Africa, but living or working in close proximity with infected animals may also allow transmission.
What will happen if we eat meat from a (dead, yet) infected animal?
The consequence of eating the meat of an infected animal would depend on the manner in which it was prepared. Raw meat would definitely be infectious.
There are conflicting reports as to whether typical cooking processes are sufficient to destroy Mycbacterium bovis bacteria, but whether these organisms would remain pathogenic has yet to be established.