More Infectious Diseases with Climate Change

We not only have to worry about extreme weather including insane megadroughts and more tornadoes with climate change, but now new research shows increased infectious diseases are also in our future.

According to findings published in the journal Philosophical Transactions of the Royal Society B, climate changes will shift habitats in a way that will bring wildlife, crops, livestock and humans into contact with pathogens that they otherwise would not be exposed to. With these pathogens ending up in new places with new potential hosts, deadly diseases such as West Nile virus and Ebola will become more common.

"It's not that there's going to be one 'Andromeda Strain' that will wipe everybody out on the planet," lead author Daniel Brooks said in a press release, referring to the 1971 science fiction film about a deadly pathogen. "There are going to be a lot of localized outbreaks putting pressure on medical and veterinary health systems. It will be the death of a thousand cuts."

Previous research has already shown the emergence of pathogens in parts outside of their native habitat as environmental dynamics change. For example, after humans hunted capuchin and spider monkeys out of existence in some regions of Costa Rica, their parasites immediately switched to howler monkeys, where they persist today. Also, in recent years lungworms have moved northward and shifted hosts from caribou to muskoxen in the Canadian Arctic. And the latest study findings indicate that similar shifts will occur as wildlife inhabits new areas to adapt to warming temperatures and changing environments.

Normally, based on an idea called the "parasite paradox," scientists assume that parasites can't just quickly jump from one species to another because of the way parasites and hosts co-evolve. Over time, hosts and pathogens become more and more adapted to one another, and so it would seem highly unlikely that new diseases would emerge.

However, Brooks and his colleagues found that pathogens can jump hosts more quickly than previously thought. 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 said.

In fact, he added, the new hosts are more susceptible to infection and get sicker from it because they haven't yet developed resistance.

But this isn't just a potential problem for humans. The researchers stress that understanding which non-human species carry different pathogens is also crucial. This has proved effective in the past in developing public health strategies to reduce the risk of infection - for example, the incidence of malaria and yellow fever has declined in some regions after public health officials helped reduce human contact with mosquitoes, known carriers of the viruses.

"We have to admit we're not winning the war against emerging diseases," Brooks added. "We're not anticipating them. We're not paying attention to their basic biology, where they might come from and the potential for new pathogens to be introduced."

By better understanding the evolutionary relationships among species, scientists may be able to anticipate the risk of pathogens spreading outside their native range and infecting new hosts.

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