[Cryptosporidium: phylogeny and taxonomy]

Members of the genus Cryptosporidium in the phylum Apicomplexa were long thought to be closely related to the coccidia. However, despite strong morphological similarities to these organisms, Cryptosporidium has notable differences with them and similarities with the gregarine protozoa. On the basis of phylogenetic analysis of molecular data, some authors place Cryptosporidium at the basis of the phylum Apicomplexa, others consider species of this genus to be phylogenetically too distant from the coccidia and do not include them in this group of protozoa, and others think that Cryptosporidium is closely related to gregarines. The taxonomy of this genus and the naming of species are undergoing rapid change due to the new and increasing molecular information. Molecular characterization of oocysts using polymerase chain reaction based procedures has not only a major impact on resolving the taxonomy of Cryptosporidium at the species level but also on the molecular epidemiology of cryptosporidiosis. Today, it is recognized that this genus is a phenotypically and genotypically heterogeneous assemblage of largely morphologically identical species and genotypes. Fourteen Cryptosporidium species and 21 C. parvum genotypes are currently recognized. Phylogenetic analyses have shown that genetically related hosts often have related forms of Cryptosporidium. Application of molecular techniques to taxonomy and epidemiology is helping to characterize new and existing species and determine the sources of the parasites that will facilitate the identification of sources of water-borne cryptosporidiosis.