Cellphones Track Malaria in Kenya
Millions of cellphone users in Kenya are helping the fight against malaria. In the Oct. 12 issue of the journal Science, scientists report using cellphone location data to create a map of
"sources" and "sinks" of malaria, which could lead to
better-focused efforts against the mosquitoes that carry it.
The researchers used location data from every call and text made by a mobile phone user in Kenya — 14.8 million of them. The location data was gathered from the 11,920 cell towers that dot the country, spread among 692 settlements. That data was used to track where people traveled. The researchers then superimposed maps of
population density and the rate of infection of malaria. The prevalence
of the number of people infected with the disease combined with the travel data was then used to establish a per-day probability that a person would be infected if they visited a specific location.
Malaria is caused by a
parasite transmitted by mosquitoes, which bite an infected person and transmit
the disease to someone else. In 2011, the disease resulted in some 655,000 deaths, 91
percent of them in Africa, according to the World Health Organization's 2011
World Malaria Report.
"We really got to work
out where the infections are coming from," Caroline Buckee, assistant
professor of epidemiology at the Harvard School of Public Health and senior
author of the study, told Discovery News.
The combination of two
"big data" sources enabled the research team to see travel patterns
and use that to find areas where most malaria infections come from. "One
of the 'great' things about malaria is that we have very high spatial
resolution maps of prevalence," Buckee said. The map of prevalence can be
broken up into areas as small as a kilometer (about a thousand yards) on a
Some people don't show
symptoms immediately, so they can be carriers. That means draining a swamp or spraying a certain area might kill the local
bugs, but if people carry the parasite from an area that is untreated, the
eradication effort won't do any good.
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The study found that many people travel from Nairobi to areas near Lake Victoria, where mosquitoes and malaria are prevalent. If infected, those travelers bring malaria back to Nairobi when they return. This is why there are more malaria cases showing up in Nairobi's clinics and hospitals than one would expect from the fact that there aren't
many places for mosquitoes (of the species that transmits malaria) to live.
Buckee noted that the study
doesn't involve finding someone with malaria and tracking their movements.
Rather, it uses the data that local officials have about malaria prevalence and
population density and combines it with the location information from the phone
companies. That's combined with mathematical models of malaria transmission. There's
no information about individual people.
Aside for malaria, Buckee
said there has been interest from other researchers in applying this method to
studies of dengue, another mosquito-borne disease that tends to show up in
tropical countries. Dengue, in fact, might be even easier to study as it tends
to show up in urban areas where there are more cell phone towers, and thus
better data on human movement.
Top image: Sources
and sinks of people and parasites. The left map shows ranked sources (red) and
sinks (blue) of human travel, while the right one shows the sources and sinks
of parasites. The biggest source of parasites center on Lake Victoria, which is
on the western side of the country, and the sink is in the area around Nairobi,
in the south-central part of the map. Travelers, by contrast, move from Nairobi
to Lake Victoria and back again.