London (AsiaNews/Agencies) – At least half a billion cases of malaria occur each year, 50 per cent more than World Health Organisation (WHO) estimates, and the disease is more serious in Southeast Asia than previously thought.

So says an international team of epidemiologists, who believe the estimates are so disastrously wide of the mark that a global attempt to control the mosquito-borne disease by 2010 is at threat.

The WHO estimates more than a million people are killed by malaria each year, and at least 300 million acute cases occur annually, 90 per cent in sub-Saharan Africa.

The new study - published in the British weekly science journal Nature - suggests that in 2002, 2.2 billion people - more than a third of the world's population - were potentially exposed to the malarial parasite plasmodium falciparum. Bob Snow, lead author of the report, said getting numbers right was important.

"Not knowing the size of the problem limits our ability to articulate how much money we need to tackle the problem - not knowing where the problem is located means you can't spend wisely."

The study puts the number of clinical infections at a "conservative" 515 million cases a year in a range of 300 million to 600 million, and says Southeast Asia accounts for about a quarter of the total.

The research  said infections outside Africa could be 200 per cent higher than the WHO estimates.

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