Global warming alarms infectious disease experts

Posted: 25 May 2007

Earth's rising temperature means trouble for health experts trying to fight infectious diseases, microbiologists said at a scientific meeting in Canada in May. ENS reports.

"One of the first indicators of rising global temperatures could be malaria climbing mountains," said Dr. Stephen Morse of Columbia University. Speaking at the American Society for Microbiology (ASM), meeting in Toronto, Morse said in mountain areas where malaria is endemic, the disease is not transmitted above a certain altitude because temperatures are too cold to support the mosquitoes that carry the disease. As temperatures rise, this malaria line will rise as well, said Morse.

Dr Stephen Morse
Dr Stephen Morse
Dr Stephen Morse is associate professor of epidemiology as well as founding director and senior resident scientist at Columbia University's Center for Public Health Preparedness. Photo courtesy Columbia University
"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," said Morse. In its April report on the impacts of climate change, the UN's Intergovernmental Panel on Climate Change 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, said David Rogers of Oxford University, also speaking at the ASM meeting. But he said that whether specific diseases will increase or decrease is much more difficult to predict, because disease transmission involves a great many factors.

malaria in blood
malaria in blood
Through the microscope: an image of malaria in blood. Photo courtesy University of Erlangen
The scientists say a combination of historical disease records and modern satellite data, plus good predictive models is needed to describe the past, explain the present and predict the future of infectious diseases.

Another change could be lengthening of the flu season, the scientists said. Influenza is a year-round event in the tropics. If the tropical air mass around the Earth's equator expands, as new areas lose their seasons they may also begin to see influenza year-round.

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, said Dr. Joan Rose a water expert in Michigan State University's Water Quality and Environmental Microbiology Laboratory.

"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," said Rose.

Rose is co-director of the newly established Center for Advancing Microbial Risk Assessment – a consortium of scientists from seven universities with expertise in quantitative microbial risk assessment methods, biosecurity and infectious disease transmission through environmental exposure. The Center is funded by the US Environmental Protection Agency and the US Department of Homeland Security.

"We are at greater risk than ever before of infectious disease associated with increasing extreme weather events," she said.

Indirect effects of climate change on infectious disease will also appear, said Morse, who warned that the effect of global warming on agriculture could lead to changes in disease transmission and distribution.

"If agriculture in a particular area begins to fail due to drought, more people will move into cities," said Morse. There, high urban 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," said Morse. "Otherwise, we can hope our luck will hold out."

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