Geneva -- Tuberculosis is mutating into dangerous, drug-resistant forms for which no cure is known, health leaders in Switzerland said.

One strain of XDR-TB, which stands for extensively drug-resistant tuberculosis, doesn't respond to antibiotics normally used to treat TB, making it virtually incurable and threatening to become a pandemic, CNN reported Monday.

The World Health Organization estimated about 40,000 new cases of XDR-TB emerge annually.

Health experts said XDR-TB shouldn't exist because TB is curable, CNN reported. But if anti-TB drugs aren't correctly administered or used, the disease can mutate into deadlier strands.

The World Health Organization said not enough money has been raised to combat the more virulent TB strains, which is linked to poverty, while drugs used to treat regular TB cost $20 a patient in the developing world.

Furthermore, no new scientific developments to fight TB have been made in more than four decades, said Louise Holly of Action, a group with the goal of controlling the spread of TB.

"The drug resistant strand is a highly contagious airborne disease," Holly said. "With increased travel and globalization, it is possible for anyone to pick up the disease, even in developed countries like the United States and (Britain)."