One-quarter of the world’s population is infected with the bacterium that causes tuberculosis. Most of these people will not show symptoms. In some people, the disease becomes ‘active’, causing symptoms and spread of the bacterium.

Our researchers are revealing why tuberculosis persists in the body, and how the immune system can be triggered to eliminate the infection.

Our tuberculosis research

Our researchers are investigating how tuberculosis-causing bacteria evade the immune system. This information is being used to develop new strategies to boost the immune response to chronic tuberculosis infection.

What is tuberculosis?

Tuberculosis is caused by infection with the bacterium Mycobacterium tuberculosis. Most commonly, tuberculosis occurs in the lungs.

People become infected with M. tuberculosis by inhaling the bacterium. Within the lungs, the bacterium is engulfed by immune cells called macrophages. For other types of bacteria, this will kill the bacteria. However, M. tuberculosis bacteria can survive and reproduce within macrophages.

Tuberculosis-infected macrophages trigger other immune cells to attack them. This leads to inflammation, with a mass of immune cells surrounding the infected macrophages.

In 90 per cent of people infected with M. tuberculosis, the infection becomes ‘dormant’. They do not show any symptoms of the infection, but the infection persists within their body.

In some people, the infection becomes ‘active’. The growth of M. tuberculosis bacteria leads to lung damage. Symptoms of active tuberculosis in the lungs include:

• Cough
• Bleeding into the lungs
• Weight loss
• Fever

When someone has an active tuberculosis infection, they are able to spread bacteria to other people through their respiratory fluids.

Occasionally M. tuberculosis bacteria can spread from the lungs to other parts of the body such as bones or the central nervous system. This can cause a variety of symptoms depending on the site of the infection, such as, for bone tuberculosis, swelling, pain and deformation of joints; or for central nervous system tuberculosis, headaches, confusion and seizures.

It is estimated that 1.8 billion people worldwide are infected with M. tuberculosis. Of these, around 10 million have active illness. Tuberculosis causes 1.5 million deaths each year.

Risk factors for tuberculosis

Active tuberculosis is more common in people who:

• Have a weakened immune system, particularly those with HIV infection
• Are malnourished
• Have diabetes
• Smoke

How is tuberculosis prevented and treated?

There is a vaccine for tuberculosis, called BCG, but it is not effective in all people. Vaccination may reduce the risk of children developing serious tuberculosis disease. Researchers are working to develop a more effective vaccine for tuberculosis.

Tuberculosis is treated with antibiotics that kill the bacteria. Treatment must be given for six to nine months to completely eliminate the infection.

M. tuberculosis can become resistant to antibiotics. The spread of these antibiotic-resistant strains is reducing the success of current treatments. The increasing prevalence of ‘multidrug resistant’ or ‘extensively drug resistant’ tuberculosis strains is leading to the possibility of tuberculosis becoming an incurable disease. Our research into new treatments for tuberculosis is focused on bolstering immune responses to clear infection.