Smoking weakens natural defences and increases risk of getting TB
Smoking weakens a person's natural defences and leaves them more at risk of contracting TB, new research has revealed.
It contributes to around 15pc of cases of TB because the smoke particles can clog up the immune system, according to a study led by Professor Joe Keane of St James's Hospital and Trinity College in Dublin.
Previous studies have shown that only around 30pc of healthy people exposed to the disease will be infected, and of those some 5pc to 10pc will develop TB.
Prof Keane said: "TB kills 4,000 people every day, and there are around eight million TB cases worldwide.
"Cigarette smoking is one of the biggest contributors to developing the disease. Until now, we didn't really know why, or how, smoking had such a profound effect."
The researchers, who included a team from the University of Cambridge, first investigated a type of immune cell called a macrophage, which is a white blood cell that is supposed to attack and engulf foreign material that gets inside the body.
However, they discovered it was not able to travel to the TB infection after it had been exposed to particles similar to those you get in tobacco smoke. They then approached Prof Keane to see if the same effect occurred in human lungs.
Prof Keane said the findings of the study, funded by the Health Research Board and published in the journal 'Cell', could have significance beyond TB and may also be linked to people who inhale air pollution.
"More than one third of the world's population cooks indoors without a chimney and gets exposed to an excessive amount of biomass fuel smoke. This material also makes the patient susceptible to TB - accounting for 22pc of cases - which is extremely common in the developing world.
"We hope that with further analysis, we can fine tune interventions that will support cigarette smokers, or persons exposed to biomass fuel, in the fight against tuberculosis."
There were 318 cases of TB diagnosed in Ireland last year and two deaths, according to the Health Protection Surveillance Centre.
Some 155 of the patients were born in Ireland; 127 cases involved foreign patients, while country of birth was not reported for 36. Of the 127 cases born outside Ireland, 11 were asylum seekers or refugees.