Climate change could be behind more than just rising ocean levels, melting polar ice caps, and extreme weather events — it could also be creating the ecological basis for infectious diseases to spread to new places and new hosts. Writing in the Philosophical Transactions of the Royal Society B, two prominent zoologists, Daniel Brooks of the University of Nebraska-Lincoln and Eric Hoberg of the U.S. National Parasite Collection of the USDA’s Agricultural Research Service, warn that outbreaks of infectious diseases such as West Nile virus and Ebola are just the start – global warming could enable similar types of diseases to emerge and thrive in places you might not expect.
The basic underpinning of this “climate change causes infectious disease” model is that warming temperatures and other forms of “climatological variation” have the potential to fundamentally change natural habitats. As habitats change, this ultimately leads to wildlife, crops, livestock and humans being exposed to new pathogens. In some cases, these pathogens find new susceptible hosts and are able to spread quickly.
If carried to an extreme, it’s an unnerving scenario — “vector-borne diseases” (think malaria) could become more and more likely, even as medical researchers thought they had figured out how to deal with most of them last century. In a worst-case scenario, subtropical and tropical diseases may end up heading to more temperate climes, such as Europe and, yes, America.
“It’s not that there’s going to be one ‘Andromeda Strain’ that will wipe everybody out on the planet,” according to Brooks. “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.” In other words, if climate change takes on greater intensity, localized outbreaks of Ebola could become the norm rather than the exception. This escalation of new outbreaks in places you wouldn’t expect would put a huge strain on the capacity of medical and health practitioners to deal with them.
This innovative thinking about the link between climate change and infectious disease overturns the current thinking on how and why diseases spread. The conventional wisdom (referred to as the “parasite paradox”) is that the host-pathogen relationship is so tightly adapted that pathogens have a hard time finding a new host species when things go wrong. Even with ecological change and habitat destruction, these pathogens would essentially have no place to turn, no “back up plan” if their hosts suddenly disappear as the result of changing habitats and ecosystems.
The new thinking, known as the “Stockholm Paradigm” (not to be confused with the “Stockholm Syndrome”), combines four different ecological concepts – ecological fitting, the geographic mosaic theory of co-evolution, taxon pulses and the oscillation hypothesis – to conjecture that pathogens may not really have as hard of a time finding a new host as we thought. They may already have the “ancestral genetic capabilities” to switch to new hosts that are genetically close enough to the original hosts.
Historical examples cited by the researchers, who have studied infectious diseases in both Arctic and tropical ecosystems, include the howler monkey (which substituted nicely for the spider monkey in Costa Rica) and the muskoxen (which took over from the caribou in the Canadian Arctic).
Of course, there is bound to be a certain amount of skepticism when people (and especially scientists) claim that, “Well, things are different this time around.” There have always been variations in climate, and there have always been “habitat perturbations.” So what’s different this time around? The answer may be that climate change is happening more rapidly than it has in the past, upsetting biodiversity dynamics in a way that has never before been possible. In layman’s terms, Darwin never thought parasites could evolve this fast.
Science naysayers, and there are more than a few of them these days, will no doubt refuse to believe this theory. If they deny global warming, it’s easy to see that they will deny the “climate change causes infectious diseases” theory. The danger, however, is that we will fail to prevent infectious diseases such as Ebola from ever starting in the first place because we won’t understand how and where they can spread.
So what can be done if we want to avoid the real-life remake of “Contagion”? One obvious answer might be to provide more funding and support to agencies that monitor and prevent outbreaks. This would help to prevent or minimize human contact with potentially infected animals. “We have to admit we’re not winning the war against emerging diseases,” Brooks said. “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.”
Another approach that might be worth adopting, says Brooks, is studying the evolutionary relationships among species, in order to predict which species will take over as disease-carriers. He suggests that there should be greater coordination between the public and veterinary health communities and members of the “museum” community who classify species. In short, one of the best ways to prevent disease outbreaks such as Ebola in the future is to look way, way back into our evolutionary past.