Image caption Smoking is a risk factor for TB

Forty million smokers could die from TB by 2050, research suggests.

Smokers are about twice as likely to get the lung infection and die from it, compared with non-smokers.

Many of the new TB cases will be in Africa, the eastern Mediterranean and Southeast Asian regions, according to projections published in the BMJ.

A lung charity said global efforts to fight TB are being undermined by the tobacco industry's "aggressive promotion" of smoking in some places.

Dr John Moore-Gillon is a TB specialist and honorary medical advisor for the British Lung Foundation.

He said: "It is nearly 20 years since the World Health Organization declared tuberculosis to be a 'global health emergency'.

"Since that time rates have risen rather than fallen, and smoking increases the risk of getting - and dying from - TB.

"Concerted international efforts are now under way to try and turn the tide of TB, but this important research shows that all these efforts may be undermined by the tobacco industry's continuing aggressive promotion of smoking in many parts of the world."

Mathematical model

Nearly a fifth of people in the world are smokers; many in countries with high rates of TB where multi-national tobacco companies have expanded their markets.

Smoking is a known risk factor for TB, and may reduce the ability of the lungs to fight off infection.

Image caption X-ray of the chest of a patient with TB

Dr Sanjay Basu and colleagues from the University of California set out to predict the impact of smoking on future TB rates.

According to their mathematical model, worldwide smoking could lead to 40 million extra deaths from TB from 2010 to 2050.

If current smoking trends continue, the number of new cases of TB will rise by 18 million.

Smoking alone could undermine the worldwide goal of reducing TB mortality by half between 1990 and 2015, they say.

Writing in the BMJ, the team concludes: "Tobacco smoking could substantially increase tuberculosis cases and deaths worldwide in coming years, undermining progress towards tuberculosis mortality targets.

"Aggressive tobacco control could avert millions of deaths from tuberculosis."

Contagious

Tuberculosis is a contagious infection that mainly affects the lungs, but can spread to other parts of the body.

If not treated, it can damage the lungs to such an extent that a person cannot breathe properly.

Sometimes, people do not experience any symptoms for many months or even years after being infected.

TB can treated with antibiotics but is sometimes fatal.