The long-standing assumption that malaria kills almost exclusively young children appears to be wrong.
Of the 1.2 million people who died of the parasitic disease in 2010, 58 per cent were under five, but 42 per cent were over that age, a new analysis shows.
The research, published in Thursday's edition of The Lancet, also reveals malaria to be much more lethal than previously believed accounting for twice as many deaths as in earlier estimates.
"We were really surprised by the results," Stephen Lin, an associate professor of global health at the Institute for Health Metrics and Evaluation at the University of Washington in Seattle, said in an interview.
"Traditionally we're taught that when you're exposed to malaria as a child you develop immunity," he said. "We found a lot of malaria deaths in the population age five and older so, obviously, that immunity is not as complete as we assumed."
Determining how many people die of specific diseases around the world is a complex task, because death registries tend to exist only in developed countries. In the developing world, scientists need to examine hospital records, surveys and use "verbal autopsies" – essentially interviews with family members that allow a diagnosis post-mortem.
Last year, Prabhat Jha, a University of Toronto professor and one of the world's best known "disease detectives," published startling research showing that malaria killed 200,000 people annually in India, far more than the official estimate of 15,000. His ongoing Million Death Study is probing all the causes of death in India.
The new research published in The Lancet is derived from a similar exercise being done on a larger scale, the Global Burden of Diseases, Injuries, and Risk Factors 2010 Study. It is the first attempt in decades to gather up-to-date statistics on how people die. Researchers say these data are essential for setting public health priorities and can lead to re-thinking of established medical wisdom – like the 'fact' that malaria kills only kids.
Dr. Lin and his team re-analyzed mortality data from 1980 to 2010 to come up with the new figures. They found that malaria deaths rose steadily through the 1980s and 1990s, peaking at 1.8 million in 2004.
The silver lining is that the death rate has fallen significantly in recent years, particularly in young children.
"We've seen a huge increase in both funding and in policy attention given to malaria over the past decade, and it's having a real impact," said Alan Lopez, head of the school of population health at the University of Queensland in Brisbane, Australia, and one of the study's co-authors.
He said the biggest contributors to the decline in malaria deaths have been the use of insecticide-treated bed nets and improved drug treatments.
A study published last year showed that having a bed-net in a home reduces the chance of a child contracting malaria by 23 per cent. A bed net costs about $10 (including the net, distribution and education), while a course of drugs known as artemisinin-combination treatments (ACTs) costs about $6.
But with an estimated 3.3 billion people living in malarial zones, efforts need to be massive to be effective.
Funding for malaria prevention now exceeds $2-billion (U.S.) annually, up from $250-million a decade ago, according to the IHME estimates. In that period, several high-profile groups have sprung up, including the Global Fund to Fight AIDS, Malaria & Tuberculosis, Roll Back Malaria, Malaria No More and Nothing But Nets.
It is estimated that some 250 million people a year contract malaria. The disease, caused by a parasite, Plasmodium falciparum, that is carried by the Anopheles mosquito. Malaria is found in equatorial zones in Africa, south-east Asia, the Middle East, and the Americas.
However, mortality occurs principally in Africa: 1.1 million of the 1.2 million deaths in 2010, according to the new research.