What is Cryptosporidium? Reappraising its biology and phylogenetic affinities

In raising the question 'What is Cryptosporidium?', we aim to emphasize a growing need to re-evaluate the affinities of Cryptosporidium species within the phylum Apicomplexa so as to better understand the biology and ecology of these parasites. Here, we have compiled evidence from a variety of molecular and biological studies to build a convincing case for distancing Cryptosporidium species from the coccidia conceptually, biologically and taxonomically. We suggest that Cryptosporidium species must no longer be considered unusual or unique coccidia but rather seen for what they are - a distantly related lineage of apicomplexan parasites that are not in fact coccidia but that do occupy many of the same ecological niches. Looking at Cryptosporidium species without traditional coccidian blinders is likely to reveal new avenues of investigation into pathogenesis, epidemiology, treatment and control of these ubiquitous pathogens.