As the world marks international Tuberculosis day, a new study has revealed a frightening rise in the past 15 years in tuberculosis cases in Africa. Correspondent Scott Bobb reports from our Southern Africa Bureau in Johannesburg.

International experts (from South Africa and the United States), writing in the New England Journal of Medicine on the eve of TB Day, say Africa is facing the worst tuberculosis epidemic since the invention of antibiotics.

They note that Africa, which is home to 11 percent of the world's population, carries 29 percent of the world's TB cases and 34 percent of its TB-related deaths. And they quote statistics of the World Health Organization as saying that from 1990 to the year 2005, the incidence of TB more than doubled, mainly in southern, eastern and central African nations.

The head of an HIV research unit at Johannesburg's Witswatersrand University, Francois Venter, says a major cause is HIV/AIDS which weakens a person's ability to fight disease.

"The risk of acquiring TB if you're HIV positive is so huge, coupled with the fact that there's so much TB floating around in this community that conventional approaches to prevention and treatment are not going to win," Venter said.

TB is a highly infectious disease that is spread through the air usually by the cough of an infected person. More than three million people in Africa are living with TB and a half-million die from it each year.

The report says that health care systems in many countries have difficulty responding to the threat because of a lack of funding, personnel, drugs and laboratories.

Venter volunteers at hospitals in less wealthy parts of South Africa.

"The numbers of patients with TB are astronomical," he said. "Every morning we do a ward around here and it's just TB, TB and more TB, a dozen different forms but all of it TB. It's scary to me that there doesn't seem to be a plan."

Tuberculosis is treatable but diagnosis can take a long time during which period the victim is in the community spreading the disease.

Experts say that many TB victims die before they are diagnosed and many who are diagnosed die anyway because they begin treatment too late.

Another aggravating factor is the emergence of TB strains that are resistant to most drugs. Almost all victims of these strains are HIV positive and few of them are ever cured.

Venter says progress against HIV/AIDS is being made thanks to greater funding, aggressive education campaigns and the growing availability of anti-retroviral drugs to fight the virus.

"We learned from the HIV program that if we support patients actively - and this means support groups, free parcels (of food), counseling, explanations - people will take their treatments," he said.

He says current TB programs are not working and as a result governments and policy makers need to declare a TB emergency similar to that for HIV/AIDS.