LONDON — Billionaire George Soros pledged $3 million yesterday to fight a deadly strain of tuberculosis in Africa.

Since an outbreak of extensively drug-resistant tuberculosis, or XDR-TB, was identified in South Africa last year, health experts have repeatedly issued warnings about the disease’s spread across the continent. But aside from a series of worldwide meetings, little concrete action has been taken.

Mr. Soros’s Open Society Institute announced a $3 million grant to the nonprofit organization Partners in Health and Brigham and Women’s Hospital in Boston. The donation will be used to design a model project of community-based XDR-TB treatment in Lesotho. Once treatment guidelines are developed, experts hope the program will be adopted in other poor countries.

Partners in Health has previously implemented community-based programs for drug-resistant TB in countries including Peru and Rwanda.

“It is possible to treat highly resistant tuberculosis,” said Dr. Paul Farmer, co-founder of Partners in Health, who disputed characterizations of the disease as “virtually untreatable.”

Last September, the World Health Organization confirmed 53 XDR-TB cases in South Africa, of which 52 were fatal. To date, more than 300 cases have been identified, and at least 30 more are found each month.

In a few weeks, WHO experts will begin helping South African authorities investigate the origins and spread of last year’s outbreak. The World Health Organization estimates $650 million is needed annually to combat the XDR-TB problem annually.

No XDR-TB cases have been found in neighboring countries like Lesotho, Malawi, or Zimbabwe, but experts suspect weak surveillance systems there are simply not picking them up. The disease has been identified in 28 countries worldwide, including all G8 countries.