Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish

Steinhausia mytilovum (Mussel Egg Disease)

Category | Common Name | Scientific Name | Distribution | Host Species
Impact on Host | Diagnostic Technique | Methods of Control | References | Citation

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Category

Category 1 (Not Reported in Canada)

Common, generally accepted names of the organism or disease agent

Steinhausia or mussel egg disease.

Scientific name or taxonomic affiliation

Steinhausia (=Chytridiopsis, =Haplosporidium) mytilovum and Steinhausia sp. (Microsporida).

Geographic distribution

a) Eastern United States (Field 1923, Sprague 1965, Figueras et al. 1991a, Sunila et al. 2004) and California, U.S.A. (Hillman 1991).
b) Europe including Italy (Lauckner 1983), Spain (Figueras et al. 1991b, Robledo et al. 1994, Villalba et al. 1997) and France (Comtet et al. 2004).
c) Cockburn Sound, Western Australia (Jones 1997, Jones and Creeper 2006).

Host species

a) Mytilus edulis and Mytilus sp.
b) Mytilus galloprovincialis and Mytilus edulis.
c) Mytilus galloprovincialis.
Steinhausia sp. and Steinhausia-like microsporidia have been reported from other bivalves including oysters and the cockle Cerastoderma edule.

Impact on the host

This microsporidian infects the cytoplasm of mussel ova and incites a strong haemocyte infiltration response. This infiltration of granulocytes and large basophilic haemocytes was associated with resorption of the germinal epithelium and ova. However, infected oocytes (=ovocytes) have also been observed in apparently healthy follicles (Sunila et al. 2004, Jones and Creeper 2006). The effect on the viability of individual ova is unknown, however, infection distorts the nucleus of the ovum and can also cause the destruction of the egg. Also, mussel fecundity is believed to be inversely related to the intensity of infection. In Cockburn Sound, Western Australia, the overall prevalence of infection was 44.4% of the female mussels in August and October 1995 (Jones and Creeper 6006). In M. edulis from Long Island Sound, Connecticut, USA with a relatively high prevalence of infection (23%), the proportion of infected ova versus uninfected ova was generally very low (Sunila et al. 2004).

The biology of Steinhausia is poorly understood. Transmission likely occurs when loose spores are released along with intact eggs or through phagocytosis and subsequent diapediasis (Jones and Creeper 2006). Vertical transmission (from one generation to the next via the ova) is suspected but not yet proven. In Western Australia, the prevalence of infection did not increase with the size of the mussel suggesting that infection is annual (Jones and Creeper 2006).

Diagnostic techniques

Gross Observations: Infected ova in the mantle tissues of cooked female M. galloprovincialis result in an uneven surface with depressed creamy white patches and swollen tubercles that form spots against the orange-pink background colour of health female tissue (Jones and Creeper 2006).

Histology: Sporocysts (parasitophorous cysts, spherical inclusions, uni-nucleate or multi-nucleate) within the cytoplasm of the oocyte or ovum and may be associated with haemocyte infiltration of the gonadal tissue (inside affected gonadal follicles and in the connective tissue surrounding those follicles) . Sporocysts spherical in shape (9-18 µm in diameter) and may contain 10 to 41 spherical spores (about 1-2 µm in diameter). Although there is usually only one sporocyst per ovum, up to three sporocysts have been observed in histological sections of the gonad of M. galloprovincialis. May be associated with indentation of the ovum nucleus.

Methods of control

Mussels from areas known to be infected (currently or historically) should not be introduced to unaffected areas.

References

Bower, S.M. and A.J. Figueras. 1989. Infectious diseases of mussels, especially pertaining to mussel transplantation. World Aquaculture 20(4): 89-93.

Comtet, T., C. Garcia, Y. Le Coguic and J.P. Joly. 2004. First record of the microsporidian parasite Steinhausia mytilovum in Mytilus sp. (Bivalvia: Mytilidae) from France. Diseases of Aquatic Organisms 58: 261-264.

Field, I.A. 1923. Biological and economic value of the sea mussel Mytilus edulis. Bulletin of the Washington Bureau of Fisheries (1921-1922) 38: 127-259.

Figueras, A.J., C.F. Jardon and J.R. Caldas. 1991a. Diseases and parasites of mussels (Mytilus edulis, Linneaus, 1758) from two sites on the east coast of the United States. Journal of Shellfish Research 10: 89-94.

Figueras, A.J., C.F. Jardon and J.R. Caldas. 1991b. Diseases and parasites of rafted mussels (Mytilus galloprovincialis Lmk): preliminary results. Aquaculture 99: 17-33.

Hillman, R.E. 1991. Steinhausia mytilovum (Minisporida: Chitridiopsidae) in Mytilus sp. in California: a new geographic record. Journal of Invertebrate Pathology 57: 144-145.

Jones, J.B. 1997. Steinhausia sp. (Microspora: Chytridiopsidae) infecting ova of Mytilus galloprovincialis in western Australia. In: M. Pascoe (ed). 10th International Congress of Protozoology. The University of Sydney, Australia, Monday 21 July - Friday 25 July 1997, Programme & Abstracts. Business Meetings & Incentives, Sydney, p. 112.

Jones, J.B. and J. Creeper. 2006. Diseases of pearl oysters and other molluscs: a Western Australian perspective. Journal of Shellfish Research 25: 233-238.

Lauckner, G. 1983. Diseases of Mollusca: Bivalvia. In: O. Kinne [ed.]. Diseases of Marine Animals. Volume II: Introduction, Bivalvia to Scaphopoda. Biologische Anstalt Helgoland, Hamburg, p. 550-553.

Robledo, J.A.F., M.M. Santarém and A. Figueras. 1994. Parasite loads of rafted blue mussels (Mytilus galloprovincialis) in Spain with special reference to the copepod, Mytilicola intestinalis. Aquaculture 127: 287-302.

Sprague, V. 1965. Observations on Chytridiopsis mytilovum (Field), formerly Haplosporidium mytilovum Field (Microsporidia?). Journal of Protozoology 12: 385-389.

Sunila, I., L. Williams, S. Russo and T. Getchis. 2004. Production and pathology of blue mussels, Mytilus edulis (L.) in an experimental longline in Long Island Sound, Connecticut. Journal of Shellfish Research 23: 731-740.

Villalba, A., S.G. Mourelle, M.J. Carballal and C. López. 1997. Symbionts and diseases of farmed mussels Mytilus galloprovincialis throughout the culture process in the Rías of Galicia (NW Spain). Diseases of Aquatic Organisms 31: 127-139.

Citation Information

Bower, S.M. (2009): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Steinhausia mytilovum (Mussel Egg Disease).

URL: http://www.pac.dfo-mpo.gc.ca/science/species-especes/shellfish-coquillages/diseases-maladies/pages/medmu-eng.htm

Date last revised:  June 2009
Comments to Susan Bower