Toby Murcott of BBC Science : "The main problem is simply the failure of basic TB control"

For the majority, the bug lies dormant, but one in 10 is likely to develop the disease which is generally triggered if the immune system becomes weakened as a result of ill health or malnutrition.

In what it calls the most exhaustive study of the disease to date involving a panel of 86 TB experts, the World Health Organization (WHO) estimates that 1.86 billion people around the world or 32% of the population carry the Mycobacteriaum tuberculosis.

But it is only in the poorest areas that the disease has developed a strong grip.

The tuberculosis bacterium usually causes an infection in the lungs, but sometimes it can affect other parts of the body.

Symptoms include loss of weight, coughing up blood and fever.

It is transmitted through the air.

In 1998 TB and five other conditions accounted for 90% of deaths from infectious disease.

Resistance

In a few areas, the bacterium has become resistant to treatment.

This is mainly because people are failing to finish the full course of treatment.

Writing in the Journal of the American Medical Association, Christopher Dye and colleagues from the WHO say there were 7.96 million new cases of tuberculosis in 1997 in the countries covered by the organisation.

Some 3.52 million of these were of infectious TB lung disease.

There were about 16.2 million existing cases of TB, of whom 23% died. In smoe African countries, more than 50% died because of the link with Aids.

Nine out of the top 10 countries affected by TB are in Africa

The scientists say the main cause of the disease's spread is ineffective measures to control and prevent it and, in Africa, its link with Aids.

They say 80% of all new TB cases were found in 22 countries.

More than half of these occurred in southeast Asia.

However, Africa accounts for nine out of 10 of the countries with the highest per capita rate of infection.