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 estimate”.
“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 has 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, belatedly, Ebola…