There were 219 million malaria cases worldwide in 2010, according to estimates from the World Health Organization (WHO), resulting in about 660,000 deaths. The disease is caused by parasites that spread to humans through the bites of infected mosquitoes, and is characterized by high fever, vomiting, and profuse sweating. It can be treated with antimalarial drugs, but receiving medicines or even bed nets can be difficult for those living in impoverished areas, and especially in sub-Saharan Africa. According to the WHO, more than 90 percent of the world's malaria deaths occur in Africa, mostly among children younger than five.

International aid groups have ramped up efforts to control malaria in recent years, with global funding rising from $100 million in 2000 to nearly $2 billion today, but the findings published in the Lancet today are something of a mixed bag. In the study, researchers from Oxford University, the Kenya Medical Research Institute, and the WHO gathered survey data on malaria parasite prevalence among children in 44 African countries where the disease is endemic. According to their analysis, 40 of these countries saw reductions in malaria prevalence among children between 2000 and 2010, while the number of people living in high transmission areas dropped from 218.6 million to 183.5 million over the same period — a 16 percent decline. In seven countries, transmission rates are so low as to render elimination a realistic possibility.

At the same time, however, the number of people living in areas of moderate or high risk of infection increased by 57 percent, from 178.6 million to 280.1 million, suggesting that rapid population growth has dampened some of the gains seen from malaria control efforts. Among those living in areas where malaria is most endemic, 87 percent live in just ten countries, including three that are not included in the WHO Malaria Situation Room — a joint initiative launched last year that provides support to ten African countries shouldering the greatest malaria burden.

In a comment on today's study, Sir Brian Greenwood of the London School of Hygiene and Tropical Medicine writes that "the reductions in malaria transmission that have been achieved in much of sub­-Saharan Africa, although encouraging, have been only modest." Greenwood also notes that this progress could be impeded by growing resistance among mosquitos to the pesticides commonly sprayed indoors or applied to protective bed nets.

Some researchers see promise in the development of malaria-resistant mosquitos and experimental vaccine treatments, but neither have proven viable thus far. In the meantime, Greenwood writes, organizations should continue to expand efforts to control the disease through traditional measures, though he acknowledges that new drugs, insecticides, and delivery methods will have to be developed and deployed before malaria elimination "becomes a credible prospect."