Compiled by
Donald W. Duszynski1, Steve J. Upton2 and Lee Couch1

1Department of Biology, University of New Mexico
2Division of Biology, Kansas State University

Comments: (Duszynski), (Couch)


The protist phylum Apicomplexa Levine, 1970 comprises a large and heterogeneous assemblage of obligate intracellular parasites of medical and veterinary significance (e.g. Eimeria, Cryptosporidium, Plasmodium, Toxoplasma). The largest subgroup of the phylum is the suborder Eimeriorina Leger, 1911, which contains organisms collectively referred to as the coccidia (Levine et al., 1980). Predominantly intestinal parasites, coccidia infect most phyla of invertebrates and all vertebrate classes. The disease they cause, coccidiosis, is recognized as the major health hazard in domestic animal husbandry, in zoo environments, and in wild animal populations when habitat is lost and overcrowding occurs. At present, the Eimeriorina has 8-13 families, 36-39 genera and >2000 named species. By far, the largest family in the suborder, Eimeriidae Minchin, 1903, with 17 genera and ~1700 species (this database) is the group that we are working to resolve on a global scale.

Working within the taxonomy of the coccidia is difficult. (1) The literature is vast and widely scattered, much of it appearing in obscure journals that have limited circulation. In consequence, literally hundreds of species descriptions remain unarchived and/or uncatalogued. The only definitive work on the group has been Pellérdy's Coccidia and Coccidiosis (1974); although Levine (1988) authored a 2 volume checklist, The Protozoan Phylum Apicomplexa, these volumes are useful as lists, but are incomplete, not cross-referenced by host, parasite, locality, author or any other way and, thus, have limited value. (2) The coccidia have a complex life cycle that includes 3 sequential stages: endogenous merogony and gamogony followed by sporogony which is exogenous. This complexity resulted in various stages of the same coccidian species being described as different species, or even placed in different higher taxa (genera to suborders), before their basic life history was understood. (3) The endogenous (intracellular) developmental stages in a coccidian life cycle are unknown in >98% of all described species and are impossible to find or identify under field conditions, so these characters have little present taxonomic value. (4) The exogenous stage (oocyst), upon which the majority of all species descriptions are based, is highly resistant to all known fixative techniques and, to date, no satifactory method is known to permanently preserve its structural features; thus, the taxonomy of coccidians has been non-specimen-based. As a result, most species are described solely on measurements of different structures in the sporulated oocyst, some additional key qualitative features, and line drawings. Even though both the Botanical and Bacteriological Codes accept line drawings as type specimens for organisms that cannot be preserved, the Zoological Code has not yet addressed this issue adequately.

These problems make sorting through the taxonomic literature on this group difficult, and differentiating species can be "best-guess" work even for an experienced taxonomist. Here we seek to catalogue all known species of coccidia within the Eimeriidae and to reference whatever information is available about each species, including, but not limited to: current terminology and taxonomic status, including synonyms; type host and other known hosts; type locality and geographic distribution; descriptive parameters of all known life history stages, including line drawings and photomicrographs (if any); pathology; unique biological details that can help distinguish a species (e.g., prepatency, patency, ultrastructure, excystation, cross-transmission studies, etc.); reference to gene sequences, if available; kinds of type material archived and their museum location(s); and complete or representative literature citations.

Accessing the Database and Additional Web Resources:

The Coccidia of Snakes of the World

Biology of the Eimeriidae

Techniques for the Preservation of Life Cycle Stages

Alphabetical List of the Coccidia


Coccidiologists of the World

Coccidiosis Conferences (2008-2014) with some Powerpoint Presentations

Molecular Sequences in the NCBI GenBank Database

Links to Other Parasitology-related Sites

The Microbiology Information Portal


In 1994, the National Science Foundation announced a Special Competition, termed Partnership for Enhancing Expertise in Taxonomy (PEET), that was initieated to train the next generation of taxonomists of poorly studied groups, mostly microorgansims. In 1995, the first cohort of 21 awards was made, including DEB 9521687, which initiated the "Coccidia of the World" project. This endeavor, a joint effort between the University of New Mexico and Kansas State University, began the task of creating a database for the scientific community that, eventually, would catalogue all known species of coccidia (Apicomplexa: Eimeriidae), their descriptions, and all biologically relevant material.

NSF-PEET and DEB 9521687-Related Resources

DEB 9521687 PEET Products


Presentations and Posters

Student Training

Ongoing Projects/Research Beyond DEB 9521687