"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

October 18, 2010

October 18 - Necator americanus

Necator americanus is a species of nematode commonly known as a hookworm. It has a very broad distribution and has long been common in the Southeastern U.S. The eggs are shed in the host's feces and then they go through several larval stages in the soil. Eventually they develop into filariform larvae, which find a host, often a barefoot kid, and burrow in through the skin in their feet. They will make their way into blood vessels, and eventually find their way to the lungs. They get coughed up, swallowed, and then mature into adults in the GI tract. They use their rather fearsome jaws to latch onto a villus in the small intestine, where they ingest the host's blood. The symptoms can be mild anemia, diarrhea, and cramping but infection can also lead to more serious things such as iron-deficiency and even developmental problems. Sounds pretty awful, right? Yet, believe it or not, many people are now becoming infected with these parasites - on purpose. The reason is that recently it was observed that people in developing countries, where hookworm and other parasites are prevalent, do not very often have auto-immune diseases like allergies, asthma, etc. and it was hypothesized that our hyper-sterile Western lifestyle that has led to "bored" immune systems that turn on our own bodies. Helminthic therapy is a new movement whereby people purposefully expose themselves to worms such as hookworm in an effort to keep their immune system busy attacking the parasite so that it doesn't cause these other problems. A documentary about this new therapy has been made - you can learn more about it here.


  1. i heard about it.. but isnt it dangerous?
    if someone gets flu or something the immune system will stay busy with the parasite and the other pathogens can go nuts.. no?
    and,does our immune system is able to kill parasites? i allways hear about people getting parasites and almost dying from it and there is allways a need of medicine. our immune system cant defeat parasites then?

  2. First, let me say that I am not an M.D., so this does not constitute medical advice. For some people with severe auto-immune issues, these worms may bring some relief and so they choose these as the "lesser of two evils", if you will. Second, our immune systems deal with macroparasites such as these worms quite differently than they deal with bacteria and viruses.

  3. I'm assuming you don't usually die after being infected?

  4. ok thanks.
    ok thank you susan :)
    by the way i have a suggestion for halloween parasite:

    " Gnathostoma spinigerum "

    i like their head. its creepy to think those little horns on the sides of the head are used to borrow through the skin.
    but i still like them.

  5. Great info! Had heard of Trichuris being used for helminthic therapy, but didn't know about Necator...
    Thanks for the great blog!

  6. This was just addressed on "Grey's Anatomy"

  7. First, you do a great job with this blog! I really like to stop by now and then to learn more about all the creatures parasitazing us.

    To this hookworm picture, however, I have to say it is not Necator, it is Ancylostoma caninum. Necator has 2 plates in its mouth, A. caninum the 2 pairs of teeth.


  8. Thanks, Verena - and you're right - I was in a hurry and grabbed the wrong photo. Here's one of the *other* hookworm - the real, Necator americanus.