GENEVA - The World Health Organisation (WHO) dramatically cut its estimate on Thursday of how many people catch malaria every year, attributing the revision to changes in research methods.

The new report, however, kept the number of people who died from the disease broadly the same.

The United Nations agency said 247 million people were infected with malaria in 2006, the most recent year for which figures are available.

Its last estimate, issued three years ago and widely cited in government and pharmaceutical circles, was that 350 million to 500 million people caught the mosquito-borne disease a year.

"The change is due primarily to a refinement of calculation methods. It is not known if cases and deaths actually declined between 2004 and 2006," the WHO said in a statement.

"The reduction is primarily due to changes in the method for estimating the number of cases outside Africa. The method for Africa remained the same," its report explained.

The WHO's global death toll from the disease, which is especially deadly for infants, children, and pregnant women, was nearly steady in the new report. It estimated 881,000 died from malaria in 2006, compared to "more than 1 million" previously.

"The global burden of malaria remains enormous," it said.

Last year the Geneva-based agency drew sharp criticism after it slashed its estimate of how many people are infected with the AIDS virus from nearly 40 million to 33 million. It said that was due to updated information on India's HIV epidemic.

Malaria has attracted huge sums of public funding in past years, channelled through the WHO as well as other bodies like the Global Fund to Fight AIDS, Tuberculosis and Malaria, the Bill & Melinda Gates Foundation and the Clinton Foundation.

The WHO's Roll Back Malaria Partnership has called for a scaling-up of funding for malaria to $3.4 billion (1.8 billion pounds) a year, from $1.2 billion to improve access to artemisinin-based drugs and insecticide-treated bed nets that can prevent infection.

Novartis AG's drug Coartem is used to treat malaria. Other pharmaceutical companies including Intercell are also working to develop a malaria vaccine.

Malaria is most prevalent in Africa, where the WHO estimates the number of cases using climate data on heat and humidity that affect mosquito breeding, combined with some sample surveys.

In Asia, it said national surveillance had improved markedly since the last global report, from 2005, so data drawn from governments were used for the latest calculations. "The earlier report relied on historic data on malaria risk in different areas," the report said.

WHO Director-General Margaret Chan said the new figures gave a clearer snapshot from which to assess malaria control efforts.

"With dramatic increases in funding and intense momentum towards reducing the malaria burden in recent years, we have a greater need for reliable information and analysis," she said in a statement. "This report begins to answer that need."