Climate change may have helped spread Zika virus: WHO scientists
The outbreak of Zika virus in
Central and South America is of immediate concern to pregnant women in the
region, but for some experts the situation is a glimpse of the sort of public
health threats that will unfold due to climate change.
“Zika is the kind of thing we’ve
been ranting about for 20 years,” said Daniel Brooks, a biologist at University
of Nebraska-Lincoln. “We should’ve anticipated it. Whenever the planet has
faced a major climate change event, man-made or not, species have moved around
and their pathogens have come into contact with species with no resistance.”
It’s still not clear what role
rising temperatures and altered rainfall patterns have had on the spread of
Zika, which is mainly spread by mosquitoes; the increased global movement of people
is probably as great an influence as climate change for the spread of
infectious diseases. But the World Health Organization, which declared a public
health emergency over the birth defects linked to Zika, is clear that changes
in climate mean a redrawn landscape for vector and water-borne diseases.
According to WHO, a global
temperature rise of 2-3C will increase the number of people at risk of malaria
by around 3-5%, which equates to several hundred million. In areas where
malaria is already endemic, the seasonal duration of malaria is likely to
lengthen. Aedes aegypti, the mosquito that carries Zika and other diseases, is
expected to thrive in warmer conditions.
As climate change reaches almost
every corner of the Earth’s ecology, different diseases could be unleashed.
Increased precipitation will create more pools of standing water for mosquitoes,
risking malaria and rift valley fever. Deforestation and agricultural
intensification also heightens malaria risk while ocean warming, driven by the
vast amounts of heat being sucked up by the oceans, can cause toxic algal
blooms that can lead to infections in humans.
“We know that warmer and wetter
conditions facilitate the transmission of mosquito-borne diseases so it’s
plausible that climate conditions have added the spread of Zika,” said Dr
Diarmid Campbell-Lendrum, a lead scientist on climate change at WHO.
“Infectious agents in water will
proliferate with more flooding. It’s clear that we need to strengthen our
surveillance and response to a range of diseases. Globalization, the movement
of people, is an important factor too. In a world where we are disrupting the
climate system we’ll have to pay the price for that.”
WHO estimates that an additional
250,000 people will die due to climate change impacts – ranging from heat
stress to disease – by 2050, but Campbell-Lendrum said this is a “conservative
“It is based on optimistic
assumptions that the world will get richer and we’ll get better at treating
these diseases,” he said. “We do need to get better at controlling diseases at
their source and we do need to drive down greenhouse gases because there is a
limit to our adaption. By moving to cleaner energy sources we will also help
relieve one of the largest health burdens we have, which is the air pollution
that kills seven million people a year.”
Until now, efforts to push back
the threat of infectious diseases have been successful. Malaria, for example,
used to be found in the New York area – and there is evidence to suggest it was
once present in southern England; much earlier, the Romans used to retreat to
the hills at certain times of the year to avoid mosquitoes carrying the
disease. Vaccines have been developed for a range of diseases including,
The eradication of threats like
these makes wealthy western countries fret over outbreaks like Zika. As the
world warms, there may be a lack of preparation for other diseases not
currently considered threats.
“This is likely to become an
equal opportunity crisis,” said Brooks. “The developing, poorer countries are
impacted disproportionately but they deal with these diseases all the time,
they are not surprised by them. But in Europe and North America, people have
lived in a bubble where we think our wealth and technology can protect us from
climate change. And that’s not true.
“The thing that worries me most
is a death by a thousand cuts. I don’t think an Andromeda strain will wipe out
all humans. But the amount of time, money and effort needed to combat these
many different problems can overwhelm a healthcare system.”
So which climate-fuelled diseases
are likely to pop up next? Some experts believe that water-borne diseases could
escalate, which would have significant consequences for countries such as Bangladesh
– a low-lying nation with plenty of rivers that has a public health system
already struggling to meet its population’s current needs.
“There’s not nearly enough
attention paid to diseases that cause diarrhoea, crypto spiridium, Hepatitis
A,” said Aaron Bernstein, a paediatrician at Harvard Medical School.
“We’ve seen outbreaks of these
diseases in the past due to extreme precipitation. The build environment we
live in wasn’t designed for the climate we will soon be living in; when you
consider half the world’s waterways have been engineered by man, they won’t be
able to contain the extra water that will flood them.
“Flooding will certainly lead to
mosquito-borne diseases but also cause water-borne diseases and also a lack of
drinking water. People in Asia and Africa, particularly those living on the
coast, will be very vulnerable, climate change could be the straw that breaks
the camel’s back in terms of public health.”