WHO ‘underestimates malaria threat by half’

A malaria-carrying mosquito from South-East Asia taking a blood meal Copyright: WHO-TDR

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The threat to human health posed by the deadliest form of malaria has been significantly underestimated, especially for regions outside Africa, according to research published today (10 March) in Nature.

The study suggests that the Plasmodium falciparum parasite caused 515 million cases of malaria in 2002 – nearly double the World Health Organization (WHO) estimate — and threatens some 2.2 billion people worldwide.

Until now, it has been thought that 90 per cent of malaria attacks caused by the parasite occurred in Africa. The new study suggests, however, that almost a quarter of cases occur in South-East Asia and the western Pacific — almost 200 per cent more than in previous estimates.

The researchers, led by Bob Snow, based at the Kenyan Medical Research Institute-Wellcome Trust Laboratories, Kenya, used new and existing data to map where people live, and predict both their likelihood of carrying malaria parasites and of their infection leading to the disease.

The disparity between the team’s findings and existing WHO estimates is because of differences in the way the two sets of statistics were calculated.

The WHO bases its estimates for South-East Asia on reports provided by the health authorities in each country. For Africa, which has the biggest malaria problem and the least capacity to face it, the WHO is more proactive.

There, it uses surveys to assess the number of malaria cases and deaths, and combines this information with figures on the risk of malaria transmission in different regions to provide a fairly accurate estimate of the disease’s impact.

According to Snow, however, the national reporting systems in South-East Asia and other regions outside Africa are almost as weak and unreliable as those in Africa.

Speaking to SciDev.Net, Snow said that in many areas where malaria is rife, people often visit private clinics or use traditional medicine rather than visiting government-run clinics, so national reports to the WHO have tended to underestimate the number of cases of malaria.

Snow stressed that his team’s research was not intended to be a criticism of the WHO — which is aware that the international community needs more accurate figures on malaria — nor was he keen to take the attention away from Africa which, as the world’s poorest continent, is least able to generate resources needed to tackle the disease.

But, he said, South-East Asia is where drug-resistant forms of malaria have emerged, and because transmission of the disease occurs at a low level in these countries, a concerted effort to drive out malaria could greatly reduce incidence of the disease.

Snow added that calculating estimates of malaria cases rigorously and scientifically would be crucial to identifying the scale of the problem and the amount of money needed to fight it.

Richard Feacham, executive director of the Global Fund to Fight AIDS, Tuberculosis and Malaria, said in a press release that the results confirm the “gross underestimation” of malaria in Africa and Asia.

He added that the fund would now “significantly increase [its] estimates of the resources needed”.

Link to full article in Nature 

Reference: Nature 434, 214 (2005)