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How Will Global Warming
Influence Infectious Diseases
As the Earth's temperatures continue to rise, we can expect a
signficant change in infectious disease patterns around the globe.
Just exactly what those changes will be remains unclear, but scientists
agree they will not be for the good.
"Environmental changes have always been associated with the appearance
of new diseases or the arrival of old diseases in new places.
With more changes, we can expect more surprises," says Stephen
Morse of Columbia University, speaking May 22, 2007, at the 107th
General Meeting of the American Society for Microbiology in Toronto.
In its April 2007 report on the impacts of climate change, the
Intergovernmental Panel on Climate Change (IPCC) warned that rising
temperatures may result in "the altered spatial distribution of
some infectious disease vectors," and will have "mixed effects,
such as the decrease or increase of the range and transmission
potential of malaria in Africa."
"Diseases carried by insects and ticks are likely to be affected
by environmental changes because these creatures are themselves
very sensitive to vegetation type, temperature, humidity etc.
However, the direction of change - whether the diseases will increase
or decrease - is much more difficult to predict, because disease
transmission involves many factors, some of which will increase
and some decrease with environmental change. A combination of
historical disease records and present-day ground-based surveillance,
remotely sensed (satellite) and other data, and good predictive
models is needed to describe the past, explain the present and
predict the future of vector-borne infectious diseases," says
David Rogers of Oxford University, also speaking at the meeting.
One impact of rising global temperatures, though, can be fairly
accurately predicted, says Morse. In the mountains of endemic
areas, malaria is not transmitted above a certain altitude because
temperatures are too cold to support mosquitoes. As temperatures
rise, this malaria line will rise as well.
"One of the first indicators of rising global temperatures could
be malaria climbing mountains," says Morse.
Another change could be the flu season. Influenza is a year-round
event in the tropics. If the tropical airmass around the Earth's
equator expands, as new areas lose their seasons they may also
begin to see influenza year-round.
And extreme weather events will also lead to more disease, unless
we are prepared. As the frequency, intensity, and duration of
extreme weather events change, water supplies become more at risk,
according Joan Rose of Michigan State University.
"Hurricanes, typhoons, tornados and just high intensity storms
have exacerbated an aging drinking and wastewater infrastructure,
enhanced the mixing of untreated sewage and water supplies, re-suspended
pathogens from sediments and displaced large populations to temporary
shelters. We are at greater risk than ever before of infectious
disease associated with increasing extreme weather events," says
Rose.
There will also be indirect effects of climate change on infectious
disease as well. For instance, says Morse, the effect of global
warming on agriculture could lead to significant changes in disease
transmission and distribution.
"If agriculture in a particular area begins to fail due drought,
more people will move into cities," says Morse. High population
densities, especially in developing countries, are associated
with an increased transmission of a variety of diseases including
HIV, tuberculosis, respiratory diseases (such as influenza) and
sexually transmitted diseases.
"I'm worried about climate change and agree that something needs
to be done," says Morse. "Otherwise, we can hope our luck will
hold out."
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