Bovine TB – The Facts
Mycobacterium Bovis often referred to as the bovine tubercle bacillus, is a member of the Mycobacterium tuberculosis complex, a group of organisms with the capacity to cause tuberculosis in humans and Animals. BovineTB or to use the correct term – Mycobacterium Bovis, is a disease caused by a specific species of bacteria called M Bovis.
BovineTB, as the name suggests, usually affects Bovine animals, such as Cattle. However, it can affect nearly all mammals, causing general illness, coughing, and, ultimately, death.
BovineTB is a ‘zoonotic’ disease – meaning that it can pass from animal to human. It can also pass to animals in the same species or animals in another species. M.Bovis is a different species of Bacteria to M.Tuberculosis which is the usual cause of TB in humans. The name tuberculosis comes from the nodules, called ‘tubercles’ that form in the lymph nodes of infected animals.
How does BovineTB spread
BovineTB is spread by contact with an infected animal. The infection occurs from inhaling infected droplets that are expelled from the lungs by coughing. BovineTB infection can also occur from direct contact with an open wound on an infected animal.
Because the spread of bovine TB is very slow, an infectious animal may infect many others before showing any clinical signs of the disease. It is also known that BovineTB can lay latent and remain undetected in infectious animals for long periods of time. It can also survive in faeces and in the environment, ie soil, for a number of years.
BovineTB can also spread through the ingestion of milk and meat from infected animals. The link between drinking milk from diseased cows and the development of scrofula, cervical lymph node tuberculosis, was established mid-19th century when more than half of all cervical lymphadenitis cases in children were caused by M. Bovis. Infection acquired through ingesting M. Bovis is more likely to result in non-pulmonary forms of the disease.
Tuberculosis is the reason we pasteurise milk. This, in addition to the immunisation of humans (BCG), has seen the number of cases reduce dramatically. It should be noted that cattle with bTB lesions are routinely discovered by slaughterhouse workers, so there is little doubt that infected meat products enter the human food chain.
How is BovineTB diagnosed?
In the UK the standard method is by using a skin test. The Single Intradermal Comparative Cervical Tuberculin Test (SICCT), is an intradermal skin test. Avian and bovine purified protein derivative tuberculins are injected into the skin in separate sites of the neck by a Veterinarian and reactions to the injections are measured and compared. The SICCT test relies on a delayed hypersensitivity reaction to injected tuberculin. Sensitised T cells recruit and orchestrate the infiltration of other cell types into the injection area thereby leading to a transient swelling, measured at the optimum time of 72 hours from the injection.
By utilising two different Mycobacterium species, the SICCT compares the reaction of the animal to each tuberculin. This increases the specificity of the test by differentiating between cattle infected with M.Bovis and those exposed to other mycobacterium and therefore sensitised to tuberculin.
Can BovineTB be treated?
There is a treatment for humans with BovineTB, however, this is a long process with BovineTb resistance to some of the drugs used by Doctors to cure M.tuberculosis. For animals, the treatment is not considered economically viable and they are euthanised and the farmer compensated by the UK taxpayer.
Whilst cattle are the main hosts of BovineTB the disease can affect all mammals, both domestic pets and wildlife.
In the UK the following animals are known to be infected with Bovine TB.
- Alpaca = 56% positive
- Sheep = 44% positive
- Deer = 36% positive (includes farmed, wild and park deer)
- Dog = 27% positive
- Cat = 25% positive
- Pig = 19% positive
- Farmed wild boar = 2%
There are many species in the UK where insufficient testing does not allow any clear indication of risk, these include wild species such as Badgers, Foxes, Mink, Ferrets, Squirrels, Otters, Seals, Hares, Wild Boar, and Moles, and farm animals such as Horses. Pigs. Goats, and Llamas.
Humans currently have a 1% incidence of bovine TB, these are primarily farmworkers that can have prolonged exposure to animals that are infected or infectious with BovineTB. At the time of writing (March 2022), there is an increasing trend for higher occurrences (live cultural positives) of BovineTB in cats and alpacas. BovineTb is found throughout the world. It is most prevalent in Africa and parts of Asia, and the Americas. Many developed countries have reduced or eliminated bovine TB from their cattle population; however, significant pockets of infection remain in Canada, the United Kingdom, the United States, and New Zealand. Until the 1920s Bovine TB was one of the major diseases of animals throughout the world. 100 years later it remains a major disease of cattle and wildlife.
To anyone reading this far, it seems clear that the solution to Bovine TB needs to be focused on the source of the disease – and that, in the UK, is intensively farmed cattle herds in cattle herds. This seems to have escaped the Ministers of DEFRA, the UK government agency responsible for controlling bovine TB.
In the last 9 years, they have licensed the slaughter of over 176,000 Badgers, at a cost of around £55 million pounds, whilst they have had to continue to pay Farmers around £100 million per year in compensation, whilst failing to achieve the claimed reduction in the incidence of bovine TB they targeted back in 2013.
The badger cull is an extensive and emotive subject that I have been personally involved in for the last 12 years. I will be sharing more information, based on science, facts, and my own experience in future blogs.
Further Reading
Tackling Bovine Tuberculosis by RSPCA
Bovine Tuberculosis by World Health Organisation
Badgers not to Blame for BovineTB by Born Free Foundation
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