In spite of what you're thinking, this is not the love child of a squid and a kernel of corn.

Also known as *cough* beaver fever (since the dam rodents are common carriers) to those hikers unlucky enough to have a run-in with this extremely unpleasant organism. Symptoms include such pleasantries as “projectile vomiting” and “explosive diarrhea”. Fortunately, I do not speak from personal experience.

This baby is the primary reason that all you outdoorspeople have to bother with bulky or foul-tasting water decontamination apparati. Unfortunately, it’s more than just annoying to people in countries with raw sewage washing down the street, who would probably gladly bother with bulky or foul-tasting water decontamination apparati if they could afford it.

So an article in the New York Times last week described a fascinating new vaccine strategy for defeating this and many protozoan parasites that rely on “coat switching”. Giardia has about 190 coat protein genes. It only needs one to function. Normally, it cycles through them one at a time about every 10 generations, yanking the rug out from your immune system each time. Someone had the bright idea to make the organism express them all at once, vastly condensing the time required for your immune system to learn them all from several lifetimes to several weeks.

Neat!

http://www.nytimes.com/2008/12/16/science/16giar.html

Its coat protein selection system is a prime example of how evolution has produced plenty of inefficiencies and life is not “perfect” (as if we needed a reminder). Instead of selecting one of its coat protein genes and only transcribing that, it transcribes *all* of them, and destroys all but the one it wants. Kinda like making dinner by cooking every recipe in the cookbook, and then tossing all the dishes but the one you’re actually having. And that’s not the only weird redundancy, according to the article. Giardia has two nuclei. No one knows why.