tuberculosis

Infectious disease caused by the bacillus Mycobacterium tuberculosis. It takes several forms, of which pulmonary tuberculosis is by far the most common. A vaccine, BCG, was developed around 1920 and the first anti-tuberculosis drug, streptomycin, in 1944. The bacterium is mostly kept in check by the body's immune system; about 5% of those infected develop the disease. Treatment of patients with a combination of anti-TB medicines for 6-8 months produces a cure rate of 80%. In 1999 there were 8 million new cases of TB and 2 million deaths. Only 5% of cases are in developed countries. Worldwide there are 16 million people with TB and 2 billion (a third of the global population) are infected with Mycobacterium tuberculosis.

In pulmonary TB, a patch of inflammation develops in the lung, with formation of an abscess. Often, this heals spontaneously, leaving only scar tissue. The dangers are of rapid spread through both lungs (what used to be called ‘galloping consumption’) or the development of miliary tuberculosis (spreading in the bloodstream to other sites) or tuberculous meningitis.

Over the last 15 years there has been a sharp resurgence in countries where the disease was in decline. The increase has been most marked in deprived inner city areas, particularly in the USA, and here there is a clear link between TB and HIV, the virus which causes AIDS. TB is the main cause of death in HIV positive individuals.

The last decade has seen the spread of drug-resistant strains of the TB bacterium. Many strains are now resistant to the two frontline drugs, isoniazid and rifampicin, and some are multi-drug resistant (MDR). Rare until its recent appearance in the USA, MDR TB is now spreading through a number of developing countries. It is untreatable and many of its victims have died. According to a 1996 WHO estimate there may be as many as 50 million people worldwide with the drug-resistant form of TB (Britain had its first case in 1995).

In 1996 Wellcome announced a $2 million project to sequence the 4.5 million base pairs that make up the genome of M. tuberculosis.