Cell Phones Track Malaria’s Spread

Researchers used mobile phone data to track malaria parasite movements across Kenya. The results may help guide the design of more effective disease control programs.

Nearly a million people die of malaria each year—mostly infants, young children and pregnant women, and most of them in Africa. The disease is caused by a single-cell parasite called Plasmodium. Female mosquitoes can become infected after feeding on an infected human. They, in turn, can infect a new person when they feed again. Malaria may bring fever, chills and flu-like illness. Left untreated, it can cause life-threatening complications.

Both the parasites that cause malaria and the mosquitoes that carry them have been extensively studied. Less well understood has been how human travel affects the spread of the disease. A team of researchers led by Dr. Caroline Buckee at the Harvard School of Public Health set out to use mobile phone data to better understand how people help spread the parasite.

The researchers estimated the daily locations of almost 15 million mobile phone subscribers in Kenya between June 2008 and June 2009. They mapped every call or text made by each person to one of almost 12,000 cell towers. They then compared the mobile users’ movements with a malaria prevalence map from 2009. Their study was supported in part by NIH’s National Institute of General Medical Sciences (NIGMS) and National Institute of Allergy and Infectious Diseases (NIAID). The results appeared on October 12, 2012, in Science.

As expected, the Kenyan travel network was dominated by the capital Nairobi, which forms a hub for human movement to and from all regions of the country. The parasite routes show that the Lake Victoria region serves as a major source of malaria. Main destinations for the parasite lay around the Lake Victoria region and in the Nairobi area.

Areas in the highly urbanized center of Nairobi had a low ratio of clinical cases to phone data estimates of imported parasites. In contrast, hospitals on the periphery of the city had a higher ratio of clinical cases to estimates based on the phone data. These patterns suggest that there is some local transmission in the residential and less developed areas, but less within the urban city center.

“This is the first time that such a massive amount of cell phone data—from millions of individuals over the course of a year—has been used, together with detailed infectious disease data, to measure human mobility and understand how a disease is spreading,” Buckee says.

Officials can employ mosquito control programs, medications and other measures such as bed nets to combat malaria. Understanding the roles that different regions play in the spread of disease can help them decide where best to direct their limited resources. Officials might also target human travel itself, encouraging travelers to alter their behaviors and focusing their surveillance efforts along high-risk routes.

—by Harrison Wein, Ph.D.