|August 12, 2013|
How will global warming affect the spread of disease?
|The recent mountain pine beetle epidemic in the northern Rocky Mountains has highlighted how a warming climate can intensify the spread of pests, a trend that reaches well beyond the realm of forests.|
Climate change is affecting the spread of infectious diseases, including those that affect humans worldwide, according to an international team of leading disease ecologists, with serious impacts to human health and biodiversity conservation. In the journal Science, the scientists said it could be important to model how disease systems respond to climate variables.
The information could help public health officials and environmental managers predict and mitigate the spread of lethal diseases, they concluded. The biggest challenge may be in separating the effects of a warming world from other factors that influence the spread of disease.
"For a lot of human diseases, responses to climate change depend on the wealth of nations, healthcare infrastructure and the ability to take mitigating measures against disease," said the University of Georgia's Sonia Altizer, who is the study's lead author. "The climate signal, in many cases, is hard to tease apart from other factors like vector control and vaccine and drug availability."
"In many cases, we're seeing an increase in disease and parasitism. But the impact of climate change on these disease relationships depends on the physiology of the organisms involved, the location on the globe and the structure of ecological communities."
At the organism level, climate change can alter the physiology of both hosts and parasites. Some of the clearest examples are found in the Arctic, where temperatures are rising rapidly, resulting in faster developing parasites. A lungworm that affects muskoxen, for instance, can now be transmitted over a longer period each summer, making it a serious problem for the populations it infects.
"The Arctic is like a 'canary in the global coal mine,'" said co-author Susan Kutz of the University of Calgary and Canadian Cooperative Wildlife Health Centre.
"Climate warming in the Arctic is occurring more rapidly than elsewhere, threatening the health and sustainability of Arctic plants and animals, which are adapted to a harsh and highly seasonal environment and are vulnerable to invasions by 'southern' species---both animals and parasites."
A changing climate also is affecting entire plant and animal communities. This is particularly evident in tropical marine environments such as the world's coral reef ecosystems. In places like the Caribbean, warmer water temperatures have stressed corals and facilitated infections by pathogenic fungi and bacteria. When corals---the framework builders of the ecosystem---succumb, the myriad of species that depend on them are also at risk.
"Biodiversity loss is a well-established consequence of climate change," said coauthor Richard Ostfeld of the Cary Institute of Ecosystem Studies. "In a number of infectious disease systems, such as Lyme disease and West Nile virus, biodiversity loss is tied to greater pathogen transmission and increased human risk. Moving forward, we need models that are sensitive to both direct and indirect effects of climate change on infectious disease."
Where human health is concerned, there is not only the direct risk from pathogens like dengue, malaria and cholera, all of which are linked to warmer temperatures, but indirect risks from threats to agricultural systems and game species crucial for subsistence and cultural activities.
"We need to transcend simple arguments about which is more important---climate change or socioeconomics---and ask just how much harder will it be to control diseases as the climate warms?" Ostfeld said. "Will it be possible at all in developing countries?"