Climate change triggers the spread of infectious diseases

Melting polar caps, more frequent and stronger storms, rising seas levels…these are some of the scenarios we typically associate with climate change.

But there is a growing body of research that shows climate change can also provide the conditions for emerging infectious diseases to spread to new places and new hosts.

There are a number of ways in which this can happen. First of all, with the overall warming of the planet, animals and insects that carry disease are able to survive in places where they previously didn’t or can thrive longer than they were able to before. For example, tick season in the Midwest is starting earlier and ending later.

Secondly, extreme weather events associated with global warming like droughts or flooding can create situations in which disease carrying insects or animals can flourish.

Finally, climate change, as well as deforestation, could be pushing humans especially those in poor communities, deeper into the wilderness to find food sources. There, they come in contact with new diseases. That’s one of the theories of why and how diseases like ebola  gain momentum.

Viruses like ebola are zoo-notic, meaning they originate from animals and can be transmitted to humans.  When ecosystems change, wildlife as well as people come into contact with pathogens that they’ve never been exposed to before. Pathogens and their natural animal co-evolve and over time the host develops resistance. That doesn’t mean that the host doesn’t get sick or spread it around. But from an evolutionary standpoint, a successful pathogen is one that is highly contagious but doesn’t necessarily kill off its host-—especially before that host has spread those nasty germs around it’s hood. 

But some pathogens—especially RNA viruses like ebola—have a tendency to mutate—and once in a while a spillover event occurs. That is, the virus can jump species from its natural host to another animal. This can have devastating impacts for the species that hasn’t encountered the disease before and has not developed any immune responses. The current ebola outbreak is believed to have originated from two year old boy in a remote village in Guinea who came in contact with bats  or bat dropping while playing in a hollow tree.

Vector borne diseases, like the ones spread by mosquitoes, are also obvious candidates for pathogens-which-relocate with-climate change. West Nile is the most often touted example. It was first identified in the 1930s in Africa. But by 1999, it had reached New York City and there are now over 5000 cases reported each year.

But it’s not the only one, which could be coming soon to a North American city near you this year.  Last year, chikungunya, another mosquito borne disease made headlines as a result of Lindsay Lohan who caught it while vacationing in French Polynesia. It’s a silly-sounding name, chikungunya (pronounced chicken-goon-ya)  but according to one report, your joints start hurting so badly you start moving around like a chicken.  Other not-so-silly symptoms include high fevers and rashes with raised lesions. And guess what, you no longer need to go on a spendy vacation in the Caribbean to get your very own case of chickungunya. As of this month, the CDC is now reporting the virus has reached nine US states, and local mosquito populations are now carriers of the virus. Just wait ‘til summer…

Exotic, deadly diseases have always existed. The only difference now is that they’re not so rare or localized. Thanks to human impacts on even the most remote environments, we’re accelerating the rate at which we come in contact with new, potentially lethal diseases. We don’t need to go to them anymore; they come to us.