Climate change has triggered the spread of infectious diseases in new places and new hosts such as West Nile virus and Ebola, says an alarming study which was published online in the journal Philosophical Transactions of the Royal Society B.
Researchers from University of Nebraska-Lincoln in the United States warn that humans can expect more such illnesses to emerge in the future as climate change shifts habitats and brings wildlife, crops, livestock, and humans into contact with pathogens to which they are susceptible but to which they have never been exposed before.
"It is not that there is going to be one 'Andromeda Strain' that will wipe everybody out on the planet. There are going to be a lot of localized outbreaks putting pressure on medical and veterinary health systems," said noted zoologist Daniel Brooks.
Brooks and co-author Eric Hoberg, zoologist with the US National Parasite Collection of the USDA's Agricultural Research Service, have observed how climate change has affected very different ecosystems. They have witnessed the arrival of species that had not previously lived in that area and the departure of others.
"Over the last 30 years, the places we have been working have been heavily impacted by climate change," Brooks said. "Even though I was in the tropics and he (Hoberg) was in the Arctic, we could see something was happening. Changes in habitat mean animals are exposed to new parasites and pathogens," he noted. Brooks calls it the "parasite paradox". Over time, hosts and pathogens become more tightly adapted to one another.
According to previous theories, this should make emerging diseases rare because they have to wait for the right random mutation to occur. However, such jumps happen more quickly than anticipated. Even pathogens that are highly adapted to one host are able to shift to new ones under the right circumstances.
"Even though a parasite might have a very specialized relationship with one particular host in one particular place, there are other hosts that may be as susceptible," Brooks pointed out. In fact, the new hosts are more susceptible to infection and get sicker from it, Brooks said, because they have not yet developed resistance.