The World Health Organisation said it is seeking $2.15 billion in its fight against drug-resistant strains of tuberculosis, amid warnings of a 'return to the pre-antibiotic era' if they spread unchecked.

Between 400,000 and 450,000 people worldwide suffer from multi-drug resistant tuberculosis (MDR-TB), and an estimated 25,000-30,000 from the more severe extensively drug-resistant TB (XDR-TB), WHO tuberculosis expert Paul Nunn said.

At least 37 countries worldwide have reported at least one case of XDR-TB, he added.

The WHO and Stop TB Partnership's 'Global Response Plan' aims to save the lives of 134,000 MDR and XDR-TB patients over the next two years, by working to better diagnose and treat 'basic' TB before drug-resistance occurs, and also to develop treatments that are effective against the new strains.

'We're anticipating, if this plan is fully funded, a tenfold increase in the number of cases diagnosed and treated for MDR-TB,' by 2007-8 from 2005, Nunn said.

Some two thirds of MDR-TB cases are in China, India and Russia, with China alone accounting for at least 140,000 cases each year, he noted.

So far, only Hong Kong has reported a case of XDR-TB, but Nunn said it would be 'rather surprising' if no such cases had occured on the Chinese mainland. The problem is that China does not have sufficient laboratory capacity to detect such cases, he said.

The WHO first became concerned about XDR-TB in March 2006, and a deadly outbreak among HIV patients in South Africa's Kwazulu-Natal province later that year only confirmed their fears, Nunn said.

In a worst case scenario, the 8.8 million annual cases of treatable TB worldwide could be replaced by an equivalent number of XDR-TB cases, he warned, noting that each one case of TB infects between 10 to 15 other people each year.

'The possibility is that you could replace that epidemic with a drug-resistant epidemic, in other words you could have 8.8 million cases of drug-resistant TB wandering around -- and then you will be back to the pre-antibiotic era,' Nunn said.

'The paradox is that the frightening XDR-TB is fully preventable by properly diagnosing people and treating them as prescribed with effective drugs,' said Leo Reichmann of the Stop TB Partnership.

Nunn echoed this point and stressed the need for a massive increase in laboratory capacity to diagnose and treat patients, particularly in the world's poorest countries.

'There is no way that we can even begin to diagnose and treat the number of patients that need to be diagnosed and treated unless we have a huge scale-up in lab capacity,' he said, noting that there are more such laboratories in South Africa alone than in all of sub-Saharan Africa.