What is bTB?
Bovine Tuberculosis (bTB) is one of the most important infectious diseases of cattle in Northern Ireland. It is caused by a bacterium called Mycobacterium bovis (M. bovis). This bacterium is closely related to other bacteria that cause TB in humans and other animals. Together they are known as the ‘Mycobacterium tuberculosis Complex.’ Bovine TB is primarily a respiratory infection and spreads via the respiratory tract between animals. However it can also infect other organs such as the gut or alimentary system. This is most often caused by the consumption of bTB contaminated raw milk.
How does bTB infection develop in the animal?
Once in the body, if the bacteria are not cleared by the body’s defence mechanisms, they can proliferate leading to a cascade of immune responses from the animal culminating in the formation of lesions or ‘tubercles’ which are damaged areas that may have a pus-filled centre that eventually calcifies or hardens. These damaged areas rarely heal and are often the main finding of infection at post-mortem. They are found commonly associated with the respiratory tract. However the bacteria may spread to other parts of the body causing lesions to form in other tissues. If this happens and several different organs are affected, this is sometimes referred to as generalised TB.
The disease generally develops slowly, so infected animals may not show symptoms for a long time after infection. Indeed during the early stages of infection lesions are not always present or visible. Therefore the absence of visible lesions does not indicate absence of infection. However infected animals can transmit infection long before any clinical signs are present.
bTB in other species
While bTB is adapted to infecting cattle it can spill-over to other species. Within NI these include badgers, deer, cats and camelids, such as alpacas and llamas.
bTB in humans
bTB can infect humans and cause tuberculosis symptoms. Fortunately due to the ongoing bTB programme in NI together with milk pasteurisation and meat hygiene inspections, infection with bTB in humans is rare in NI. Typically 5-10 cases of bovine TB are detected in humans in Northern Ireland each year. These infections are often in people who are in close contact with infected animals.