The new study was led by Simon Hay of Oxford University's Department of Zoology and is published today in PLoS Medicine.
This estimate of how many people become ill because of the disease (which kills about 1m people a year) is almost double the previous one provided by the World Health Organization (it estimated 247m for 2007) and highlights the difficulties of tracking a global disease.
MAP, which is mainly funded by the Wellcome Trust, set out to tackle some of the uncertainties surrounding the number of cases of malaria gobally: estimates for the disease are made particularly difficult because in places where it is endemic diagnosis is often inaccurate and national reporting of cases incomplete.
The researchers used a recently published map of modern-day malaria risk and more advanced statistical techniques that better describe uncertainty. They found that there could have been between 349-552m clinical cases of P. falciparum worldwide in 2007 and came up with a combined estimate of 451m cases.
They also discovered that more than half of the estimated malaria burden and its associated uncertainty was contributed by India, Nigeria, the Democratic Republic of Congo, and Myanmar (Burma).
'The uncertainty in our knowledge of the true malaria burden in a mere four countries, confounds our ability to assess progress in relation to international development targets at the global level. It is clear that we urgently need an increased focus on reliably enumerating the clinical burden of malaria in these nations,' Simon told us.
'The divergence in our estimates and those of the World Health Organization is greatest in Asia and acute in India. We have sought to explore on a country by country basis how these differences arise, the relative uncertainty in the alternative burden estimation approaches and the potential insights that could be gained by hybridising the two.'
Oxford University's Bob Snow, who leads the MAP group in Kenya, said: 'Our estimates for P. falciparum malaria alone are almost twice those provided by the WHO, which include both P. falciparum and P. vivax malaria.'
Bob added: 'Getting the numbers right is fundamental to reporting on success or otherwise of increased donor funding. A valid question remains about whether agencies charged with the responsibility of supporting the delivery of malaria interventions should be the same ones expected to report progress.'