Definition of "giardia"

Some of those that have been found in swimming pools are viruses such as hepatitis A, bacteria such as Pseudomonas aeruginosa, which can produce severe ear ache, and the parasite giardia, which can cause a nasty stomach upset.

1999 July 13, Jacqui Wise, “Murky waters”, in The Guardian‎

As soon as the immune system has generated antibodies against one coat, giardia switches to another.

2008 December 16, Nicholas Wade, “A Coat of Many Proteins May Be This Parasite’s Downfall”, in The New York Times‎