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Parasites look set to become more virulent because of climate change, according to a study showing that frogs suffer more infections from a fungus when exposed to unexpected swings in temperatures.
"Increases in climate variability are likely to make it easier for parasites to infect their hosts," Thomas Raffel of Oakland University in Rochester, Minnesota said. "We think this could exacerbate the effects of some disease," he said of the report he led with colleagues at the University of South Florida. It is published in the journal Nature Climate Change.
A UN panel of experts says that global warming is expected to add to human suffering from more heat waves, floods, storms, fires and droughts, and have effects such as spreading the ranges of some diseases. And climate change, blamed on greenhouse gases released by burning fossil fuels, is also likely to mean more swings in temperatures.
"Few...studies have considered the effects of climate variability or predictability on disease, despite it being likely that hosts and parasites will have differential responses to climatic shifts," the authors wrote.
The scientists exposed Cuban tree frogs in 80 laboratory incubators to varying temperatures and infections of a fungus, Batrachochytrium dendrobatidis, which is often deadly for the amphibians.
Temperatures the frogs were kept in
In one experiment, frogs kept at a temperature of 25 degrees Celsius (77F) for four weeks suffered far more infections when they were shifted to incubators at 15C (59F) and exposed to the fungus than frogs already used to living at 15C. "If you shift the temperature a frog is more susceptible to infection than a frog that is already adapted to that temperature," Raffel said.
In another test, frogs that were exposed to predictable daily temperature variations between 15 and 25 Celsius, typical of shifts from night to day, were much better at resisting the fungus. Based on factors including their size, life expectancy and factors such as metabolism, the scientists said frogs probably took 10 times as long as fungus to acclimate to unexpected temperature changes.
Raffel said that more tests were needed of other parasites and hosts to confirm the findings. "This study was only done on a single tropical frog species," he said.
He said he was unaware of studies about how other parasites such as malaria, for instance, might be affected by temperature swings that affect both its mosquito and human hosts. "It's an open question," he said. Still, he said that there was speculation that cold-blooded creatures such as frogs, insects, reptiles or fish might be more susceptible to parasites as temperature shifted than warm-blooded birds and mammals.
(Reuters Health, Alive Doyle, August 2012)
