Smoking could be responsible for 40 million excess deaths from tuberculosis between 2010 and 2050, says a new study.

The study, undertaken by Dr Sanjay Basu from the Department of Medicine at the University of California San Francisco (UCSF), was published online in the journal BMJ.

The study says there will be 18 million more cases worldwide between 2010 and 2050 because smoking increases the risk of contracting TB.

The study says nearly one five persons smoke. The countries likely to be most affected by new smoking-linked TB are in Africa, Southeast Asia and the Eastern Mediterranean.

A mathematic model of smoking trends and smoking's impact on TB risk has been used for deriving at the estimates.

The researchers estimated the effect of decreasing the use of tobacco. If smoking rates were aggressively lowered, the TB deaths linked to smoking could decrease by 27 million by 2050.

TB usually attacks the lungs, but can also affect other parts of the body. It is spread through the air when people who have an active TB infection cough, sneeze, or otherwise transmit their saliva through the air. The classic symptoms are a chronic cough with blood-tinged sputum, fever, night sweats, and weight loss.