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 2005 there were 8.8 million new cases of TB and 1.6 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.

From the 1990s 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). According to a World Health Organization (WHO) report published in February 2008, multidrug-resistant tuberculosis is on the increase worldwide. The untreatable form of extensively drug-resistant tuberculosis has been recorded in 45 countries. The WHO estimated that $4.8 billion would be required for Tb control in 2008, with a funding gap of $2.5 billion.

The complete genome sequence of M. tuberculosis was decoded and published in 1998.