"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

February 1, 2010

February 1 - Echinococcus granulosis

When people think of tapeworms, they often think of very long ones, like Taenia saginata. Echinococcus granulosis is a tiny tapeworm – tiny, but nasty. The main vertebrate hosts of E. granulosis are canids, where the 5 millimeter-long adult tapeworms live in the small intestine. Eggs are expelled in the dog’s feces, where they are eaten by herbivores such as sheep or deer or rodents. Inside the herbivore, the larvae travel through the intermediate host’s blood and take residence in various organs where they form hydatid cysts, which can grow very large in some cases – as big as a grapefruit or even larger. It is thought that these cysts make the herbivore more vulnerable to predation by – canids, of course. Humans can serve as intermediate hosts if they are exposed to contaminated dog (or coyote or wolf or other canid) feces and will suffer from hydatid disease when the larval tapeforms form cysts in our organs. This can be a serious condition, not only because the large cysts can put pressure on organs, but also because should the cysts rupture within the body, a person can suffer from severe shock. The disease can be common in areas with many sheep.


  1. For some reason, the focus of this parasite in an episode of "House" really stuck with me. Details here.

  2. Hi-
    I'm working on my doctorate in historical archaeology, specifically looking at parasites and parasitic disease in archaeological contexts so I was very happy to find your blog! Hydatid cysts are an indication of parasitic disease that can appear archaeologically, if the cyst calcifies and is found along with the person's remains. It doesn't happen often but there are cases in the literature, usually from medieval cemeteries.
    Fun stuff!

  3. That is super cool, Diane! I am a big fan of archaeological parasitology.

  4. Thanks- I'm glad you think so! My family thinks I'm terminally odd, but I find that parasites can provide so much information about diet, sanitation, environment and more that they're a great area of archaeological research. Now I just have to write the dissertation...

  5. I hope your credible because you just answered my question that I have been searching for awhile thanks:)