High risk. Childhood infection rates are 10% in light green areas and more than 50% in dark green. Yellow is unclassified, and grey is unpopulated or not at risk.

Malaria Prevalence Worse Than Thought

A new global map of malaria incidence suggests that 50% more people are suffering from the disease than previously thought.

Malaria affects millions around the world, but a reliable estimate of those infected and at risk from the disease has been difficult to come by. In many parts of Africa, children suffer more than one clinical bout of malaria each year, resulting in death or life-long health problems from delayed treatment. Most often public health officials and aid agencies do not know which regions are most affected.

So scientists from the University of Oxford based at the Kenyan Medical Research Institute in Nairobi set about drafting a map of the extent of Plasmodium falciparum, the mosquito-borne parasite that causes malaria. Using data from international travel advisories, the World Health organization (WHO), and journal reports of the disease, they identified areas dense with the parasite or relatively free of it. "We excluded areas of high altitude and those with a high density of concrete buildings as these cannot support malaria," explains Bob Snow, an epidemiologist with the institute. Combining these data produced a map of malarial burden indicating that in 2002 alone there were 515 million cases worldwide. This is 50% more than reported by the WHO. "We now think that at least 2.2 billion people are at risk from malaria," says Snow. Moreover, Africa bears a much larger brunt of the disease than other parts of the world.

The new estimates, reported this week in Nature, imply a significantly higher price tag for beating the disease. "Donor agencies underestimate the amount of money and medicine required. So it is important we get the numbers right," Snow says.

"This is a very nice study," says Nirbhay Kumar, a malaria researcher at the Johns Hopkins Malaria Research Institute in Baltimore, Maryland. "Lots of people suspected the total disease burden was higher, and the researchers have used established data to prove this." The burden would have been even weightier, he adds, if the team had included Plasmodium vivax, the parasite that affects much of South Asia.

Related sites

Kenyan Medical Research Institute
WHO info on malaria
Abstract of Nature paper