Friday, 15 July 2011

Must We Hate Worms?

Is the revulsion we feel toward intestinal worms (in fact, anything called a parasite) innate or learned? If we hadn’t been surrounded by the “yuck factor” all our lives, grossed out by anything that wriggles or crawls, would we view them with disgust or curiosity? I think it would be more in the realm of curiosity.

In his book Parasites and Parasitic Infections in Early Medicine and Science, R. Hoeppli describes early attitudes toward parasites. Even within the last few hundred years, many people believed they arose spontaneously from intestinal contents, blood, even dust and ashes. And “in China,” he writes, “there existed from ancient times the widespread belief that one should have at least three worms in order to remain in good health” (p. 164).

Robin M. Overstreet has investigated the deliberate ingestion of parasites for various reasons by humans and found that parasites are often deliberately eaten and sometimes even regarded as delicacies (“Flavor Bugs and other Delights,” Journal of Parasitology: 89(6)). Overstreet describes a boy “open[ing] the intestine (of a possum) where a lump existed to allow the tapewoms to squirt out, remov[ing] the feces from the worms, and drop[ping] each writhing organism straight into his mouth.”

A former co-worker described an encounter with a small boy who was playing with a rather large roundworm, whirling it around while holding on to one end. When asked where he got it, he calmly indicated that it had come out of his nose.

These things suggest that a horror of worms is not a natural characteristic of humans. Similarly, Hans Zinsser writes that “as wise a man as Linnaeus suggested that children were protected by their lice from a number of diseases” (Rats, Lice and History, p. 139).

[caption id="attachment_301" align="alignleft" width="249" caption="Portrait of Carolus Linnaeus by Alexander Roslin, 1775"]Linnaeus, by Alexander Roslin[/caption]

I’ve often suggested that if it were possible to keep mosquitoes out of your back yard, it would be socially unacceptable to have any there. I believe that’s what’s happened to parasites. If they were unavoidable, we’d accept them as part of life, like mosquitoes and mud puddles. In the handful of decades since we’ve been able to avoid having parasites in developed countries, we’ve also learned to abhor them.


  1. I am still in the first chapter of Parasites, and I'm already interested in bringing it to my students. I teach HS advanced life sciences and focus a great deal on global health issues, especially those that are water related. How could I bring S. hematobium into my classroom? I love the historic continuity of water borne disease (that might sound creepy, like when I tell my students cancer is so cool). Where are regions that are struggling with schistosomiasis currently, I might be able to have them conduct some investigations?

  2. The schistosomas are indeed "so cool." Three main things make them - I think - particularly compelling:
    - They live in the blood (which shows that you don't really have to make anything up if you're writing horror fiction). Early attempts at treatment involved actually filtering them out.
    - They have a complex and fascinating life cycle. Seeing them live is amazing, but not possible for most people. There are some good videos of various stages on the internet.
    - It seems unlikely that an organism with such a demanding life cycle would become a significant health issue, yet the schistosomas have done, and it's our own behavior that's made it happen. This is something that people in the West find difficult to grasp.
    Schistosoma spp. still infect millions - the Middle East, Africa, the Far East, and the Caribbean are all still seriously affected. Schistosoma hematobium is of major concern in northern Africa and the Middle East.
    I hope you enjoy the rest of the book, and thanks so much for commenting.