Cryptosporidiosis of Clams


Category 3 (Host Not in Canada)

Common, generally accepted names of the organism or disease agent

Cryptosporidiosis of clams.

Scientific name or taxonomic affiliation

Cryptosporidium sp. of the phylum Apicomplexa and class Sporozoa, normally occurs in the gastro-intestinal and/or respiratory tract of vertebrates, this is the only know occurrence in a marine molluscan species. Positive identification can not be established until all life cycle stages of this parasite have been found.

Geographic distribution

Estuarine region of the south of Portugal.

Host species

Tapes (=Ruditapes) decussatus.

Impact on the host

Found in the branchial epithelium of clams from an area where high clam mortalities occurred.

Diagnostic techniques

Histology: Several ovoid to piriform uninucleate merozoites (1.6-1.8 µm long and 0.6-0.8 µm wide) within a parasitophorous vacuole within gill epithelial cells that were frequently lysed.

Electron Microscopy: About 54 merozoites per parasitophorous vacuole each with a typical apical complex formed mainly by conoid (consisting of about 16 longitudinal microtubules), rhoptries, polar ring and subpellicular microtubules.

Methods of control

No known methods of prevention or control.


Azevedo, C. 1989. Ultrastructural observations of Cryptosporidium sp. parasite of Ruditapes decussatus (Mollusca, Bivalvia). Journal of Invertebrate Pathology 54: 23-27.

Citation Information

Bower, S.M. (1996): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Cryptosporidiosis of Clams.

Date last revised: September 1996
Comments to Susan Bower

Date modified: