The World Health Organisation on Wednesday urged donors to stamp out multidrug-resistant tuberculosis after the number of the hard-to-treat strains of the lung disease doubled in recent years.
In a progress report to mark World TB Day on Thursday, the WHO and partner agencies estimated that the number of new cases of MDR tuberculosis would reach two million between 2011 and 2015 if it is left unchecked.
"MDR-TB is a threat to all countries as it is difficult and expensive to treat," said Michel Kazatchkine, executive director of the Global Fund to Fights AIDS, Tuberculosis and Malaria.
"Unless we make an extraordinary effort to tackle this problem our ability to finance and secure continued progress against TB in general will be threatened," he added in a statement.
The WHO estimated that $900 million would be needed over the next four years to reach the target of treating one million people with such strains. Some 50,000 people are currently receiving treatment.
In 2009, 9.4 million people became ill with all types of tuberculosis and 1.7 million died of the disease, according to the WHO.
An estimated 440,000 cases of MDR-TB occurred in 2008, the last year for which data was available, including 150,000 deaths.
"Despite all the progress that has been made, the response is far from sufficient," warned Mario Raviglione, head of the UN health agency's Stop TB campaign.
MDR-TB fails to respond to standard anti-tuberculosis drugs, making it much more complex and costly to treat and increasing the threat that it will spread much more widely especially in poorer environments where it thrives.
Rifat Atun of the Global Fund said the number of resistant strains "has doubled in recent years" and were continuing to progress.
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