warming could lead to a significant increase in malaria
cases in densely populated regions of Africa and South America unless
disease monitoring and control efforts are increased, researchers said.
is global warming?
In a study of the mosquito-borne
disease that infects around 220 million people a year, researchers from
Britain and the United States found what they describe as the first hard
evidence that malaria creeps to higher elevations during warmer years and back
down to lower altitudes when temperatures cool.
More severe and fatal infections
This in turn "suggests that with progressive global warming, malaria
will creep up the mountains and spread to new high-altitude areas," said
Menno Bouma, an honorary clinical lecturer at the London School of Hygiene
& Tropical Medicine (LSHTM).
And because people who live in these areas have no protective immunity
because they are not used to being exposed to malaria, they will be
particularly vulnerable to more severe and fatal cases of infection, he added.
According to World Health Organisation (WHO) data, malaria infected around
219 million people in 2010, killing around 660 000 of them – the vast majority
in sub-Saharan Africa.
But robust figures are hard to establish for a disease that affects mainly
poor communities in rural areas of developing countries, and some global health
experts say the annual malaria death toll could be double that.
climate change and co-evolution
Bouma's study, published in the journal Science, stretched back more than 20
years to when the LSHTM first collected data on malaria and climate in the
Debre Zeit area of central Ethiopia.
Neutralising the potential threat
It had been predicted that malaria as a disease could be especially
sensitive to climate change, because both the Plasmodium parasites that cause
it and the Anopheles mosquitoes that spread it thrive as temperatures warm,
Some researchers have argued, however, that socio-economic improvements and
more aggressive and effective mosquito-control efforts would have large enough
positive effect on the spread and intensity of malaria to neutralise the
potential threat of changing climates.
Seeking evidence, Bouma and colleagues from the University of Michigan
analysed data from Ethiopia and Colombia, looking at malaria case records from
the Antioquia region of western Colombia from 1990 to 2005 and from the Debre
Zeit area of central Ethiopia from 1993 to 2005.
By excluding other factors that influence malaria case numbers, such as
mosquito-control programmes, resistance to anti-malarial
drugs and fluctuations in rainfall, they found that the median altitude of
malaria cases shifted to higher levels in warmer years and back to lower levels
in cooler years.
This yielded "a clear, unambiguous signal that can only be explained by
temperature changes", they said.
"This is indisputable evidence of a climate effect, said Mercedes
Pascual from the University of Michigan. "Our findings . . . underscore the
size of the problem and emphasise the need for sustained intervention efforts
in these regions, especially in Africa."
The researchers noted that their work was limited to two countries on two
continents, and suggested it should be replicated in more countries with
malaria in highland regions before more general trends are assumed.
change ups malaria
change: South Africans worried
to fight malaria