It is responsible for the condition isosporiasis, which causes acute, non-bloody diarrhoea in immunocompromised individuals.
At least 248 species have been described in this genus, but most of them are little studied and it is doubtful whether all should be recognized as distinct species. Some have proposed splitting those species with paratenic hosts into separate genera Levinia or Cystoisospora, but as of 1997 this had not been widely accepted.
- David S. Lindsay, J. P. Dubey, and Byron L. Blagburn (January 1997), "Biology of Isospora spp. from Humans, Nonhuman Primates, and Domestic Animals", Clinical Microbiology Reviews 10 (1): 19–34, PMC 172913, PMID 8993857