KAMPALA -- Scientists meeting here for an annual congress warned Thursday that Malaria was becoming increasingly difficult to contain, as the Organization of African Unity said the mosquito-borne disease was claiming the life of at least one person in Africa every 30 seconds.

Calling malaria one of the biggest killers in sub-Saharan Africa, the OAU said that 2,500 children under five were dying of the disease daily in a region with 90 percent of the global incidence of 300 to 500 million cases.

The OAU figures were released in Kampala at an annual gathering of medical researchers marking Malaria Day in Africa.

The pan-African organization agreed with research conducted by the UN World Health Organization showing that the main victims of the disease remained women and children living in poverty.

Malaria, it warned, was starting to show its face in areas from where it was previously thought eliminated, mainly because of poor surveillance and the growing resistance of malaria to modern medicines, especially the cheaper anti-malarial, chloroquine.

"Most patients in sub-Saharan Africa cannot afford new drugs because they are too expensive," Professor David Bradley, chairman of a special workshop on malaria at the five-day annual African Health Science Congress (AHSC), told AFP.

"Research has indicated that in most countries, 70 percent of primary school children have malaria parasites in their blood," Bradley said.

He said the way forward would be to introduce new drugs, but cautioned that the disease "could also become resistant to even these drugs."

WHO in its roll back malaria campaign is urging nations to switch to a new type of combination therapy when they find conventional treatments, like chloroquine, no longer work.

The Chinese drug artemisinin was singled out at the workshop as being among those which have handled resistance parasites best, but it remains expensive.

WHO recommended nations switch as required to artemisinin-based combination therapies (ACT), which it has added to its essential medicines list.

"WHO has worked with a variety of partners, including the manufacturers, to reduce the prices of ACTs in developing countries," said Who Director-General Gro Harlem Brundtland. "it is important that countries which need ACTs are able to access and use them in a sustainable manner."

The Kampala workshop also noted that the use of insecticide-treated bed nets was the most successful way of guarding against malaria, and could lower incidents of the disease by 34 percent.

The workshop reported that sub-Saharan Africa would need between 12 and 53 billion dollars (13 and 59 billion euros) a year to roll back the malaria pandemic.

Researchers in Kenya, meanwhile, announced Thursday the launch of clinical tests of a trial U.S. vaccine for malaria.

The vaccine, which has already been tested for safety on 60 U.S. civilian and military volunteers, was developed by the U.S. Walter Reed army Institute of Research in collaboration with Glaxosmithkline biologicals.

The meeting was told by the OAU that in the impoverished west African nation of Niger, malaria remains the main killer. Malaria Day was marked in Niger with radio and television advertisements, and it was also publicized in neighboring Ivory Coast, Sierra Leone, Togo and Benin.

Two years ago to the day, African leaders meeting in the Nigerian capital, Abuja, resolved to try and cut malaria deaths in half by the year 2010, and called on member nations to lift all taxation on treated nets, medicines and other anti-malarials.