If all parasites disappeared, the world would look very different, and not for the better.
Photo via Wikimedia Commons
Parasites are generally portrayed as ruthless organisms that give and refuse to take, living off their host organism in a non-symbiotic relationship. However, parasites actually play a very significant, and even beneficial, role in the world.
Scientists estimate that around 50 percent of all organisms are parasitic. “There's a huge universe of parasites,” parasite expert Andres Gomez of ICF International in Washington, DC, told the BBC. “They are abundant, ubiquitous, diverse, and important.”
If we managed to get rid of all the parasites, the world would look very different and the difference would be noticeable almost immediately.
“Within hours, millions of poor people would be cured of serious chronic illness like malaria, schistosomiasis, and ascariasis,” Kevin Lafferty of the US Geological Survey in Santa Barbara, California also told the BBC. “People would be able to work harder and enjoy their lives more. Their livestock and crops would be healthier too.”
But, according to the “hygiene hypothesis,” our immune systems have evolved to cope with a certain amount of infections. So if we aren't exposed to parasites and other diseases when we’re young, our immune systems don’t develop properly and can start attacking our own bodies. This is a potential explanation as to why so many people today, especially the ones living in clean environments, suffer from allergies and autoimmune diseases. Or why parents think exposing their kids to chicken pox is a good idea. If we lived in a vacuum where we weren’t exposed to any parasites, we could potentially suffer from more (and more serious) autoimmune diseases.
The circle of life would also be disrupted with the absence of parasites, because they regulate the number of plant-eating insects and other pests. Within months, the number of pests would escalate rapidly and seriously damage food crops, according to Lafferty. As a result, we’d be forced to use more pesticides, which in turn would affect wildlife.
The BBC also warns that parasite-free oceans could turn into bodies of water that more closely resemble scummy roadside ponds. Even sex could be negatively impaced in the absence of parasites.
Ultimately, these largely unwelcome microscopic guests actually benefit us more than they hurt us. In research published in 2014, Luis Zaman of the University of Washington in Seattle used a computer model to simulate the evolution of organisms. He found that parasites force their hosts to become more complex. When he suddenly removed the parasites, the host animals became much less complex, and much more alike.
In real life, Zaman hypothesizes that removing parasites wouldn’t just make other organisms simpler and less diverse. “My bet would be that we would see even more drastic rates of extinctions,” Zaman told the BBC. “Research has shown many times that parasites are important drivers and maintainers of diversity.”