Warming climate reveals links to infectious disease


The Herrold family harvests oysters in Willapa Valley, Wash. Scientists fear a warming climate is helping pathogens - such as those sometimes found in seafood - extend their reach. Photo by Bill Dewey, Taylor Shellfish Farms, Inc., courtesy NOAA.

April 5, 2012

Researchers are gaining new insight into how pathogens will react to a warmer future: 'It's not just a summer disease. It's becoming a spring and fall disease now.'

by Brett Israel

The Daily Climate

ATHENS, Ga. – Diarrhea, cholera and tick-borne illness: As the climate changes, a host of health threats are predicted to escalate, experts say. 

Temperatures and rainfall will have an "overwhelming" effect on tick-borne disease. Strong winds could spread anthrax. West Nile virus is susceptible to changes in temperature and rainfall.

Environmental changes already underway are allowing public health experts to establish stronger links between global warming and infectious disease.

An analysis of pathogens in Europe that pose a serious threat to humans or animals, such as anthrax and cholera, found that climate change could influence 60 percent of these diseases. That's "a remarkably high number," said Matthew Baylis, an epidemiologist at the University of Liverpool in the UK, who presented his work this week at a symposium on infectious diseases and climate change at the University of Georgia.

He predicts temperatures and rainfall will have an "overwhelming" effect on tick-borne disease. Strong winds could spread anthrax. West Nile virus is susceptible to changes in temperature and rainfall.

vibrio-250Baylis noted that outbreaks of these diseases have not been common. In a 2008 study of 335 human disease outbreaks between 1940 and 2004, only 10 were identified as climate-related: One fungal, three via mosquitoes and six from non-cholera vibrio, a bacterium that can cause food-borne infections.

Window for infection

In the United States, most vibrio infections are in the Southeast, typically from oysters, said Erin Lipp of the University of Georgia. The region's warm water and moderate salinity is perfect for summer outbreaks, with 95 percent of infections between May and October. But as the salinity of the region's waters changes, that window for infection is widening, according to recent data.

"It's not just a summer disease," Lipp said. "It's becoming a spring and fall disease now."

In developing countries, diarrhea, which is a symptom of gastrointestinal infection, is one of the biggest health concerns. Diarrhea kills 2.5 million children each year, but little data about diarrhea and climate exists. Karen Levy, an environmental epidemiologist at Emory University in Atlanta, found that rotavirus, which causes diarrhea, becomes more active in tropical regions when the climate is cooler and drier. Levy will soon focus on predicting how other triggers of diarrhea - norovirus, a highly contagious bug and the leading cause of food-borne disease outbreaks in the United States, is her group's next target - will change with the climate. 

Of course, predictions are just that. With some diseases, humans can break climate's influence, Baylis said. In the past there was "no doubt" that malaria was a climate-related disease, he added, but having spent billions of dollars on mosquito nets and other interventions, researchers now believe the disease can be controlled

"There's no simple picture here," Baylis said.

Photo of vibrio courtesy Tina Carvalho, University of Hawaii at Manoa, via National Institute of General Medicine Sciences.

Brett Israel is a staff writer for DailyClimate.org and EHN.org. 

DailyClimate.org is a foundation-funded news service covering climate change. Contact editor Douglas Fischer at dfischer [at] DailyClimate.org



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