On Earth Day, Remember Parasites

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Many people eat the tiny pea crabs that live in shellfish. Image by Kikkiwikiwaki: CC BY 3,0

Why Do People Need Parasites?

Beyond the argument that parasites are important for keeping the natural world in balance, here are five good reasons we should try to keep them around:

  • Immune system modulation: There’s increasing evidence that some parasites interact with the host immune system and protect us from inappropriate immune responses. We’ve lost most of our parasites in the industrialized world, and this may at least partly explain the current epidemic of autoimmune disease, allergy, and inflammatory bowel disease.
  • Environmental indicators and remediators: Some parasites accumulate heavy metals in their tissues, thereby removing them from the environment and from hosts’ bodies. In a similar way, parasites can be used as environmental sentinels that tell us when something is amiss.
  • Medicine: Some parasites have turned out to be useful medically. Leeches are commonly used to re-establish blood circulation in injured tissues, maggots are being used to clean up ulcers and wounds that don’t heal, and a spiny headed parasitic worm of fish was recently the inspiration for a new and better form of bandage. We can only guess what drugs or inspirations are yet to be discovered in the world of parasites.

  • Host protection: Having the parasites that evolution provided can protect you from being infested by other species that transfer over from other hosts. Those unfamiliar parasites may be worse than your own, or they may carry disease causing organisms with them. Rob Dunn and colleagues also point out that the loss of host species tends to encourage more generalist parasites – parasites that can live on various different hosts – and this is likely to lead to more diseases jumping from one species to another, potentially us.
  • Some parasites are good to eat or culturally important: Two good examples are the tiny gourmet pea crabs that infest shellfish; and mistletoe, a parasitic plant that is an iconic part of Christmas.

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