Since the 1970s, the highlands of East Africa
have witnessed a surge in malaria outbreaks.

Because the mosquitoes
that carry the disease do not thrive in cooler climes some researchers
have suggested a link between this rise and climate change. A 2002
study found no such connection, but a new analysis of the
data–including five more years of records–seems to show that a modest
increase in temperature could lead to a population boom in mosquitoes
and, therefore, malaria.

Mercedes Pascual of the University of Michigan–whose previous
research helped link cholera outbreaks and the El Nino Oscillation–and
her colleagues used temperature data from the Climate Research Unit in
the U.K. stretching back to 1950, the same data used by the 2002 study
but with five more years of records subsequently added. Looking at the
records for four highland spots where malaria has been on the rise–
Gikongoro in Rwanda, Kabale in Uganda, Kericho in Kenya and Muhanga in
Burundi–they found an overall warming trend of 0.5 degree Celsius
since the late 1970s.

team then fed these temperatures, along with rainfall information, into
a computer model built to simulate mosquito population dynamics in
Hawaii. Even though the temperature change was quite small, its effect
on mosquito abundance was quite large. For example, although the
temperature rise represented just a 3 percent change for these areas,
it led to as much as a 40 percent change in mosquito abundance in
Kericho and more than 100 percent in Kabale in the simulation.

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Kabale showed an especially large increase in
mosquito population because it was among the highest, and therefore
coldest sites they modeled. The number of mosquitoes in these areas is
typically small, owing to the chilly conditions. But even a small
increase in temperature in these locales can quickly tip the balance in
the insects’ favor, leading to more mosquitoes and, hence, more vectors
for the malaria parasite. On the other hand, Pascual and her colleagues
point out, warming could dry out the pools in which the mosquitoes
breed if temperatures continue to climb or rainfall patterns change.

By David Biello