Steinhausia sp. (Cockle and Clam Egg Disease)


Category 3 (Host Not in Canada)

Common, generally accepted names of the organism or disease agent

Cockle egg disease, Microsporidiosis of cockle/clam eggs.

Scientific name or taxonomic affiliation

Steinhausia sp., Steinhausia-like microsporidian. Comtet et al. (2003) speculated on possibility that the parasite in cockles may be Steinhausia mytilovum because infected populations of mussels were located in the vicinity of the infected cockles.

Geographic distribution

Europe including Spain (Carballal et al. 2001) and France (Comtet et al. 2003).

Host species

Cerastoderma edule. In addition: microsporidian parasites have been reported from the ova of the clam Macoma balthica in Maryland, U.S.A. (Farley 1977); a Steinhausia-like microsporidian was observed inside the ovocytes of the clam Ruditapes decussatus in Galicia, Spain (López et al. 1994); Steinhausia-like sporonts were reported from the ova of the clam Protothaca staminea in Alaska, U.S.A. (Unknown 2012); and Steinhausia-like microsporidian parasites were detected in the cytoplasm of oocytes of the clam Anomalocardia brasiliana in Santa Catarina State, southern Brazil (da Silva et al. 2012).

Impact on the host

All infections occur in the cytoplasm of cockle and clam oocytes (=ovocytes) and ova within the gonadal tissues. Prevalence of infection in cockles from Baie des Veys, France ranged from 11.8% to 20.0% in buried and surface cockles respectively (Comtet et al. 2003). In southern Brazil, the prevalence in clams from one area was 7.5% and the sporocysts (about 20 μm in diameter) contained spores in different development stages (da Silva et al. 2012). The intensity of infection is usually low with no or local, minor haemocyte infiltration but without significant pathological damage to the host. However, Steinhausia sp. could affect the viability of the infected ova and possibly reduce fecundity.

Diagnostic techniques

Squash Preparations: The parasite is evident microscopically within the ova in wet mount preparations of the gonadal tissue pressed between a glass slide and coverslip.

Histology: Sporocysts (usually elliptical to circular in shape from 16 to 31 μm in diameter) containing up to 30 spherical spores (2 to 3.2 μm in diameter) within the cytoplasm of well developed oocytes and mature ova. Although there is usually only one sporocyst per ovum, two sporocysts were observed in a few oocytes. Generally, the morphology of the Microsporida in cockle eggs resembles that of Steinhausia mytilovum in Mytilus spp. and Steinhausia ovicola in Ostrea edulis.

Methods of control

Cockles and clams from infected populations, or cockles/clams grown in proximity to infected populations, should not be introduced into unaffected areas.


Carballal, M.J., D. Iglesias, J. Santamarina, B. Ferro-Soto and A. Villalba. 2001. Parasites and pathologic conditions of the cockle Cerastoderma edule populations of the coast of Galicia (NW Spain). Journal of Invertebrate Pathology 78: 87-97.

Comtet, T., C. Garcia, Y. Le Coguic and J.P. Joly. 2003. Infection of the cockle Cerastoderma edule in the Baie des Veys (France) by the microsporidian parasite Steinhausia sp. Diseases of Aquatic Organisms 57: 135-139.

da Silva, P.M., A.R.M. Magalhães and M.A. Barracco. 2012. Pathologies in commercial bivalve species from Santa Catarina State, southern Brazil. Journal of the Marine Biological Association of the United Kingdom 92: 571-579.

Farley, C.A. 1977. Neoplasms in estuarine mollusks and approaches to ascertain causes. In: Kraybill, H.F., C.J. Dawe, J.C. Harshbarger, R.G. Tardiff (eds.) Aquatic Pollutants and Biologic Effects with Emphasis on Neoplasia, Vol. 298. The New York Academy of Sciences, New York. pp. 225-232.

López, M.C., A. Villalba and M.J. Carballal. 1994. Evolution of pathologic conditions affecting clams, Ruditapes decussatus, from cultured beds of Ria de Arousa (Galicia, N. W. Spain). In: Agenda and Abstracts of the Sixth International Colloquium on Marine Pathology in Aquaculture (PAMAQ 6), Montpellier, France, 28-30 April 1994, p. 51.

Unknown. 2012. Steinhausia and other unidentified microsporidia, pp. 34-35. Internet publication see bivalvediseases/steinhausia_and_other_microsporidia.pdf.

Citation Information

Bower, S.M. (2012): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Steinhausia sp. (Cockle and Clam Egg Disease).

Date last revised: November 2012
Comments to Susan Bower

Date modified: