One of the largest genetic investigations into the microbe which causes TB shows the germ followed early humans out of Africa at least 70,000 years ago, scientists say.

In a parallel probe, investigators also said they had identified 39 new genes that drive dangerous drug resistance in this germ, Mycobacterium tuberculosis.

TB is one of the deadliest diseases in the medical lexicon.

Untreated, it kills roughly half the people it infects.

Even today, in the era of advanced antibiotics, it causes between a million and 2 million deaths each year, mainly in developing countries.

Drug designers are embroiled in an arms race with the germ, hoping to outflank it with new treatments before it develops resistance to existing ones.

Writing in the journal Nature Genetics, researchers led by Sebastien Gagneux of the Swiss Tropical and Public Health Institute compared the DNA of 259 TB strains from around the world. They used this to build a “family tree” of the germ, using genetic mutations as a kind of molecular clock to show its pace of evolution. (AFP)