Sunday, March 25, 2007

What is a Parasite?

According to Stedman's Medical Dictionary, a parasite is "an organism that lives on or in another and draws its nourishment therefrom."

This definition is, admittedly, broad.

Most would agree that a worm that lives in the intestinal tract of another organism and draws blood and nutrients from its host is a clear example of a parasite.

A body louse (pictured on the upper right of this page) that feeds on humans is also a parasite. In this case, it is an ectoparasite; it that lives on the outside of its host.

In contrast, a bacterium that lives in the mouth of a healthy individual without causing any notable harm is NOT considered to be a parasite.

But what happens when this same bacterium invades the throat and causes severe pharyngitis, known to most as "Strep throat." Is it now considered a parasite?
A bit harder to answer.

The same question could be applied to viruses and fungi.

Finally, would a human fetus inside the womb be considered a parasite? I'll let you answer that one for yourself.

For the purpose of this blog, I will limit my definition of a parasite to an organism that is phylogenetically unrelated to its host, lives in or on its host, and is a eukaryote. The latter excludes bacteria and viruses. By tradition, fungi are also excluded (although they are also eukaryotic). Our focus will be parasites of humans, although I'll likely throw in an odd reptile or amphibian parasite just for fun. Enjoy!


Alex said...

Check Out Rip and Read for your official welcome to Blog-World.

Anonymous said...

will future posts have pictures? it gives the non-parasitologists a chance to see things we normally wouldn't.

Alex said...

By the way-- how many different common cold virusis crop in a given year? 1, 2, 1000s, 1,000,000s?

Any idea, Parasite Gal? Perhaps you could do a post on this.

ParasiteGal said...

No politic boy, "virusis" are not parasites. Didn't you read my post?

ParasiteGal said...

To K: of course there will be pictures! Lots of creepy dreadful wonderful pictures to go with my parasites. There's a feature parasite coming soon, I promise.

Anonymous said...


Let's have some more info!!