HONG KONG, March 28 (Reuters) - People who carry a mutant gene can develop potentially fatal meningitis if they get infected with the drug resistant Beijing strain of tuberculosis, a study in Vietnam has found.

Tuberculous meningitis is the most severe form of the disease in which the infection spreads to membranes enveloping the brain and the spinal cord. One in three people who develop TB meningitis dies, even if he or she gets hospital treatment.

The study published in the open-access journal PLoS Pathogens (http://www.plospathogens.org/doi/ppat.1000034), found people most likely to develop TB meningitis were those who carried a variant of the TLR2 gene and who get infected with the Beijing TB strain, prevalent in Asia and the former Soviet states.

Previous studies have linked TLR2 to the immune system and it seems to be important for recognising and initiating a defensive response to the TB bacteria.

The researchers took bacteria samples from 187 patients who suffered tuberculous meningitis and 236 other patients who suffered the more common pulmonary tuberculosis.

Most of the patients then had their genes analysed to see if they carried the TLR2 variant.

"Together, these results suggest that the association of the (variant gene) with tuberculous meningitis is strongest among those infected with the Beijing lineage," the scientists wrote.

The "Beijing" family of TB strains is prevalent in Asia and former Soviet states. It has become more drug resistant in recent years and has been responsible for outbreaks of multi-drug resistant tuberculosis in the United States.

More than one-third of the world's population is infected with TB and the infection rate is one every second. However, only one in 10 infected persons will develop symptoms and that usually happens when their immune systems are weak.

Left untreated, TB kills half its victims. The disease kills over 2 million people each year.

One of the researchers, Maxine Caws at the Hospital for Tropical Diseases in Vietnam, said the latest finding was a reason to develop more sophisticated and targeted treatments and vaccines.

"This is particularly important in this era of emerging 'untreatable' bacteria infections due to antibiotic resistance," Caws wrote. (Reporting by Tan Ee Lyn; Editing by Sanjeev Miglani)

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