Also In This Issue

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Connecting the Dots

Will Bugs Creep North as Climate Heats?

People on the Move as the World Warms

From the Front Lines of the Global AIDS Fight

A Photographer’s Encounter in Kroo Bay

Charting Malaria’s Demise

Eliza Barclay

 

The great 20th century battle against malaria, one of the most widespread and intractable infectious diseases on the planet, began in the 1940s, with famously mixed results. While 100 countries, like the United States, were able to successfully eradicate it, insecticide-spraying initiatives failed or never reached many of the worst affected areas, namely sub-Saharan Africa.

Today the vector-borne disease remains endemic in more than 100 countries, with some 247 million cases annually, though it is largely preventable and treatable. In 2007, the Bill & Melinda Gates Foundation helped mobilize a new funding and research effort to eradicate the disease. But many questions remain about how to do it. Among the challenges of designing public interventions to vanquish malaria once and for all is the dearth of well-organized data on which regions are at risk, and to what extent.

Most countries conduct prevalence surveys on the deadliest parasite that causes malaria, Plasmodium falciparum, to estimate how to extend prevention and treatment. But there have been next to no "risk maps" showing the scope of the problem worldwide that can guide policy-makers and donors in developing regional strategies.

A study released in March 2009 in the Public Library of Science journal PLoS Medicine is a breakthrough in visualizing the geography of malaria endemicity. The study accompanies a new geostatistical modeling tool, called the World Malaria Map - the result of two years of work by a team of researchers at Oxford University and other institutions who collaborate on the Malaria Atlas Project - that will likely help public health experts shrink malaria's reach on the world map.

Simon Hay, an infectious disease epidemiologist at the University of Oxford and the study's lead author, and the other researchers, which include geographers, statisticians, epidemiologists, biologists and public health specialists, began by looking at the scientific literature available on malaria going back to 1985. They assembled the data and then "geo-positioned" it, giving it a point indicating its location and place in time. That process took about a year. Then the researchers followed up with individual countries and institutions, requesting additional information where available. The resulting map has 8,000 data points up to 2007, with layers of uncertainty where data is insufficient.

One of the study's most hopeful findings is that although some 2.4 billion people live in places where they risk infection, 1 billion people inhabit places where transmission of the disease is low enough that interventions already in use - like bed nets, indoor residual spraying, and drugs - could be deployed to eliminate it.

"Using these techniques and future iterations, we will be able to understand in which part of the world we are making the greatest impact on the disease," said Hay.

In the Americas, for example, endemicity is around 2 percent, Southeast Asia is around 10 percent, and Africa is about 30 percent with regional variation. Hay says that this means that it would be technically feasible to eliminate malaria in the Americas in the near future.

Other results were more surprising. According to Hay, the map unexpectedly revealed that prevalence in West Africa remains high.

"It seems that this region is proving more resilient to interventions than most," Hay said.

Until the recent ramp-up in funding from donors like the Global Fund, the U.S. President's Malaria Initiative, and the Bill & Melinda Gates Foundation, countries like Nigeria did not have efficient malaria control programs, and were not collecting adequate prevalence data.

"Countries that have huge populations ... add a disproportionate amount of uncertainty into global assessments of the malaria burden," Hay noted.

Mary Ann Lansang is director of the health advisory unit for the Global Fund to Fight AIDS, Malaria and Tuberculosis, a multilateral donor that has financed the distribution of some 70 million bed nets and 74 million malaria drug treatments to date.

"The framework for evaluation of the impact of P. falciparum control efforts world-wide ... will be crucial ... in meeting the global goals for decreasing the burden of malaria cases and deaths," Lansang said.

Lansang also noted that the Millennium Development Goal on malaria - to halt by 2015 and began to reverse the incidence of malaria - will not be successful unless malaria control programs in Africa receive more support. According to the 2008 U.N. development goals report, the distribution of insecticide-treated nets and effective malaria drug use has fallen short of global targets.

Prior to the PLoS Medicine study, the most recent global map of P. falciparum endemicity was published in 1960 and lacked specific descriptions of the input data used and estimates for the uncertainty in its predictions. The statistical methods used to construct the new map make it possible to quantify the uncertainty in the results.

Though the map will help public health officials better understand endemicity and risk on a regional and global scale, malaria experts say it will be less useful for small geographic areas or country-level planning.

According to Richard Cibulskis, an epidemiologist with the World Health Organization's Global Malaria Programme, the map is imprecise at the country level in part because it can't take into account the recent scaling up of malaria programs.

But Robert Snow, a co-author of the World Malaria Map and a professor at the University of Oxford and director of the Malaria Public Health & Epidemiology Group at the Kemri-Wellcome Trust Research Programme, says that in Kenya, for example, the maps have guided the revision of the national malaria strategic plan.

To improve country level data, many countries are developing their own endemicity maps, mainly supported by Global Fund grants.

There are other limitations to the Malaria Atlas Project maps, depending what the user wants to get out of it.

"You don't get a clear idea around seasonality of disease and being able to represent the year-to-year variability. When you take a standard map, and if you look at Tanzania, and compare wet and dry years, it might be very different from the map you actually have," said Madeleine Thomson, a senior research scientist who studies malaria at the International Research Institute for Climate and Society at Columbia University. "The advances [in the World Malaria Map] would be to characterize seasonality and variability where that matters."

The Oxford researchers plan to update the map annually, establishing a continuous record of malaria control and elimination efforts that can serve as a guide for funding priorities. They now have access to 17,000 surveys, more than double the number available for the 2007 map, an increase Hay says is due to the fact that many donors and nations see the value of national prevalence surveys and committing the financial and logistic resources to make them happen.

Hay and the team will eventually turn this map into revised burden estimates. They'll also map the extent and burden of the less deadly, but neglected P. vivax parasite, which also causes malaria and accounts for more than 50 percent of cases outside of Africa.

But ultimately the map will need to be used by policy-makers and donors, who are confronting obstacles like communication when reaching out to malaria endemic regions.

"While there may be some hope in some areas to eliminate malaria we must equally use these maps and facts to remind us that Africa remains the hardest nut to crack and needs increased financial resources to dent transmission intensity," said Snow.

With better maps, policy-makers and donors may at least lend a hand in the right places.

Eliza Barclay is a freelance journalist based in Washington, DC whose work has appeared in The Atlantic and The New York Times.