Can Parasites Ever Be the Good Guys? MBL's Biology of Parasitism Course Challenges What We Think We Know
Michael Povelones was on Devil’s Lane in Woods Hole, checking a mosquito trap run by the Cape Cod Mosquito Control Projects’ Gabriella Sakolsky when he felt a mosquito land on his leg.
"When I hit mosquitoes now, I'm not super rough," he said with a laugh. "I kind of hit it a little bit, grabbed it and asked her, 'What is this mosquito?'"
Days later, under a microscope at the Marine Biological Laboratory, that same mosquito revealed a surprise—it was teeming with parasites.
The discovery became an impromptu lesson for students in the Marine Biological Laboratory's Biology of Parasitism (BoP) course, an internationally recognized program that has trained generations of parasitologists. The parasites were Crithidia fasciculata, a species the faculty had searched for in previous years without success. This year, however, the discovery came by chance after students brought the mosquito Povelones had caught back to the lab. “It was just a drop the mic moment,” said Povelones, an associate professor of biology at Villanova and co-lead of BoP’s cell biology module.
Although the Biology of Parasitism course participants hadn't found Crithidia fasciculata in previous years, Povelones said the parasite itself is far from rare.
"It's a good parasite. Good parasites don't harm their hosts," he said. "Crithidia typically is not something that's deleterious to the mosquito. This one specializes in mosquitoes, but there are other species of Crithidia that infect bees, beetles—you name it."
Just down the hall, another insect parasite is under investigation. This one has a different host: a waxworm.
An infection of 100 nematodes in a waxworm can balloon to 50,000 to 80,000 in just a week. These tiny worms like to live in insects that reside in the soil, and when those insect hosts die the nematodes will emerge into the soil looking for new insects to parasitize.
While these nematodes are deadly to insects, they are considered helpful by gardeners. “They sell these nematodes at stores like Home Depot, Lowe's, and Amazon as beneficial nematodes for your home garden,” explains Adler Dillman, a professor at the University of California Riverside and co-lead of the cell biology module.
Even some human parasites may not be all bad. While they can and do cause harm, there is evidence that we coevolved to live with parasites, and some researchers are even studying if their secretions could be beneficial to us.
“It kind of circles around this idea called the hygiene hypothesis, that in our ancient past we were not really hygienic,” explains Dillman. The idea is that if you have parasite exposure as your immune system is developing, “it helps to train your immune system for what it should recognize and when it should be active and when it's inappropriate to be active,” he says. Our bodies “shouldn't recognize gluten as a pathogen or pollen as a pathogen or our own cells as a pathogen,” and one reason these mistakes may occur could be because “we now are so hygienic that the immune system is not fully appropriately trained because it hasn't had these parasite partners to interact with.”
For the students in the MBL's Biology of Parasitism course, those unanswered questions are exactly what make the field so compelling. Armed with new techniques and guidance from leaders in parasitology, they're preparing to tackle the next generation of discoveries—perhaps even uncovering more ways that parasites may be partners rather than villains.