The World Health Organisation (WHO) sharply cut its estimate on Thursday of how many people catch malaria every year, saying rapid urbanisation in Asia had destroyed the forest habitats of disease-spreading mosquitoes.
In a report, the WHO said 247 million people were infected with malaria worldwide in 2006, the latest period for which figures are available. Its prior estimate, widely cited by governments and drugmakers, was that 350 million to 500 million people were afflicted every year.
The new report also reduced the global death toll from the disease from the United Nations agency's previous reading, which was issued three years ago, by about 10 percent.
"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 report concluded that 881,000 people died from malaria in 2006, compared to previous estimates of "more than 1 million" annual deaths from the disease that kills mostly infants, children, and pregnant women.
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 a year, from $1.2 billion, to improve access to artemisinin-based drugs and insecticide-treated bed nets that can prevent infection.
Attempting to work out the global prevalence of disease is not an exact science, and public health experts are often forced to make large-scale revisions to their estimates.
Last year, the WHO cut its estimate for those infected with the AIDS virus to 33 million from 40 million after it received new data about the epidemic in India. And the U.S. Centers for Disease Control and Prevention last month raised by 40 percent its estimate of how many Americans catch HIV each year because it adopted more precise reporting methods.
Less than one-third of the WHO's 193 member states have reliable systems to monitor and document diseases such as malaria, whose initial symptoms closely resemble the flu, WHO Director-General Margaret Chan told a news briefing in Geneva.
She said the malaria report will now be issued yearly so that decision-makers have up-to-date information on the disease. "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.
Novartis AG's drug Coartem is used to treat malaria, and other pharmaceutical companies including Austria's Intercell are also trying to develop malaria vaccines, though none are expected on the market for several years.
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.
Nigeria, the Democratic Republic of Congo, Uganda, Ethiopia, and Tanzania were among the countries with the most malaria deaths in 2006, the WHO said. Outside Africa, the countries most affected included India, Myanmar, Bangladesh, and Indonesia.