As the global climate warms, parasite-borne wildlife diseases will move north, with animals in far-northern cold regions and high altitudes expected to suffer the most dramatic increase, warns study published on Friday in the journal Science.
The study predicts an increasing spread over the next five decades of wildlife diseases caused by infectious bacteria, fungi, viruses and worms. There are serious implications for humans, says co-author Jason Rohr of the University of Notre Dame, Indiana.
“We know that 75 per cent of emerging infectious diseases have a wildlife origin,” said Rohr, who runs an ecology and public health laboratory in Notre Dame. “We should be concerned about our own health when we see studies that suggest there may be an increase in infectious disease in wildlife.”
Climate change is already causing a surge in wildlife diseases, the study notes. And people are already infected with diseases that come from wildlife, including COVID-19, Rohr said.
The study supports the theory of the “thermal incompatibility” of wildlife disease, finding that cold-adapted species are at greater risk when their habitats are warm and warmly adapted species are at greater risk when their habitats cool down.
It is based on records of 7,346 wildlife populations that include 1,381 terrestrial and freshwater species, from small insects to large mammals across all seven continents. It uses past climate records and various scenarios for future climate conditions over the next five decades to calculate trends for parasites that spread wildlife diseases.
At current carbon emission and warming rates, the study found, those parasites will increase “sharply” in prevalence at high latitudes and high altitudes, some doubling by 2070 in many boreal and mountainous locations.
If warming is slowed down, however, there will be “a much, much smaller increase in infectious disease in wildlife,” Rohr said.
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Cold-blooded animals – including amphibians, fish and insects – are at greatest risk of being unable to regulate body temperatures to adapt to warming conditions, said Jeremy Cohen of the University of Wisconsin, the study’s first author, by email.
Mammals in cold climates can partially offset heat stress by adjusting their body temperatures, said Cohen, who began his research with Rohr at the University of South Florida. Still, parasites such as ticks that infect mammals with diseases will develop faster and reproduce more in warming conditions, Cohen said.
“So warm weather is creating the perfect storm for parasites to proliferate in northern areas, where they may not have been able to thrive before,” he said.
The study does not break down risks by animal species. That is the subject of ongoing research, Rohr said. The study does not consider marine ecosystems; there is not enough information available about marine systems for use in the disease spread model, Rohr said.
Arleigh Reynolds, head of the One Health Research Center at the University of Alaska Fairbanks, said the study likely underestimated the model.
“I think the scope of the problem is even greater,” he said, citing the study places like the Northern Slope of Alaska where new animal diseases are emerging.
Dr. Richard Ostfeld, a disease ecologist who was not involved in the study, although the study’s “huge data sets” were excellent, it was limited to studying the effects of temperature.
Climate change is also affecting precipitation, increasing the frequency of extreme events, which also affects the incidence of infectious diseases, said Ostfield, with the Cary Institute of Ecosystem Studies in Millbrook, New York.
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