A new, untreatable form of tuberculosis is striking up to 30,000 people a year, the World Health Organization said on Friday, and warned it could spark an "apocalyptic scenario" if unchecked.

The United Nations agency appealed for $2.15 billion to combat drug-resistant TB under a program which it said could save up to 134,000 lives over two years.

Extensively drug resistant TB (XDR-TB), a form virtually immune to antibiotics, has been reported in 37 countries in all regions since emerging in 2006, according to the WHO.

"There is somewhere between 25,000 and 30,000, we roughly estimate, cases of extensive drug resistant TB each year," Paul Nunn, coordinator of WHO's Stop TB Department, told a briefing.

"Ultimately, to face down this epidemic, we need new tools -- we need new drugs, we need new diagnostics," he added.

The recent case of an American man with XDR-TB who traveled abroad triggered an international health scare, highlighting the potential risks of rapid spread.

XDR-TB cases are particularly difficult to treat, and a patient could infect other people for years, according to Mario Raviglione, director of the WHO's Stop TB Department.

"That is the big threat here. If you have more and more of these cases, you will automatically magnify the problem by having transmission going on to other individuals ... Once they become infected they are sort of a time bomb," Raviglione said.

"If this is kept unchecked and goes on, then you may also see an apocalyptic scenario where the present epidemic of TB is replaced by an epidemic of TB which is now fully resistant to everything," he added.


Some 8.8 million people each year develop normal TB, a bacterial infection that usually attacks the lungs and which kills 1.6 million people a year, according to the WHO.

About 450,000 get a multi-resistant form (MDR-TB) each year which is resists the main first-line drugs, but XDR-TB occurs when there is resistance to even second-line drugs.

"The possibility is that you could replace that epidemic with a drug-resistant epidemic, in other words you could have 8 million cases of drug-resistant TB wandering around. And then you will be back to the pre-antibiotic era," said Nunn.

An outbreak in KwaZulu-Natal province of South Africa last year confirmed the WHO's fears about XDR-TB, which killed 52 of the 53 patients, mainly carriers of the HIV virus, he said.

"We really now have to focus on problems of infection control. We can't allow drug-resistant MDR or XDR to get into populations of HIV-infected people," he added.

Regular TB can be diagnosed with a microscope, but drug-resistant forms require laboratories which can do more sophisticated tests -- a capacity lacking in many poor countries, especially in sub-Saharan Africa, he said.

"The reality of the situation right now is that we only have the drugs that we have and very likely we will not have new drugs for at least another 5 to 10 years," Nunn said.