The organism known as cryptosporidium is more accurately known as Crytposporidium parvum, a protozoan parisite which affects not only humans, but dogs, cats and other mammals. Other species in the genus infect fish, birds, amphibians and reptiles. Other than parvum, the species muris, baileyi, serpentis, meleagridis, wrairi, nasorum, saurophilum, felis, andersoni and molnari exist. Some of these species are able to cross taxonomic barriers, such as C. felis, which can infect both humans and cats.

The taxonomy of the Cryptosporidia is as follows:

Superkingdom: Eukaryota
Kingdom: Protozoa
Phylum: Apicomplexa
Class: Perkinsiea
Subclass: Coccidia
Order: Eucoccidiidae
Suborder: Eimeriina
Family: Cryptosporidiidae