Microsporidosis of Crabs


Category 4 (Negligible Regulatory Significance in Canada)

Common, generally accepted names of the organism or disease agent

Sick crab disease, Cotton crab, Cooked crab disease.

Scientific name or taxonomic affiliation

  1. Agmasoma (=Thelohania) spp., Amesoma (=Nosema) spp., Pleistophora (=Plistophora) spp., and probably species of other genera.
  2. Nadelspora canceri.
  3. Adelspora portucalensis.

Geographic distribution

  1. Ubiquitous, but prevalence usually very low.
  2. Along the United States Pacific Coast from Bodega Bay, California to Gray's Harbor, Washington with prevalences lowest in open oceans (0.3%) and highest in estuaries (usually about 14% but up to 41.2% in one location).
  3. Region of Aveiro, Portugal.

Host species

  1. Most marine crustacea including many species of crabs as well as lobsters, shrimp and prawns. Microsporida have also been reported from freshwater crustaceans such as crayfish.
  2. Cancer magister with infection prevalance often 2.5 times higher in male than in female crabs.
  3. Carcinus maenas.

Impact on the host

Microsporidia invade and replace host tissue such as muscle, heart, gonads, gills, and hepatopancreas, depending on species involved. They cause lysis of infected and adjacent cells and internal biochemical imbalance. Infections may be chronic but are probably eventually lethal. Product is unmarketable.

Nadelspora canceri in C. magister was directly transmitted to juvenile and adult crabs in the laboratory by allowing them to ingest infected tissue and to megalope and early juveniles by placing them in a suspension of 106 spore/ml. Clinical infections were evident in 0-age juveniles 2 months post exposure and in yearling crabs within 3 months. Also, spores from crabs with infections of a least 2 months duration were capable of transmitting the parasite (Olson et al. 1997).

Diagnostic techniques

Gross Observations:

  1. Infected tissue appears opaque while crab is still alive.
  2. Infected tissue appears opaque while crab is still alive.
  3. White xenomas irregularly dispersed in the hepatopancreas but most frequently observed on the periphery of this organ.

Squash Preparations:

  1. Microsporidian spores in muscle. Identification to genus and species based on spore size, shape, and number of spores per sporont.
  2. Spore morphology unique: long (about 10 µm) and needle shaped (0.2 to 0.3 µm in diameter), tapering to a posterior pointed end.
  3. Not reported.


  1. As for squash preparations.
  2. As for squash preparations.
  3. One uninucleate schizont giving rise to two sporonts, each originating two sporoblasts, resulting in two spores within a persistent sporophorous vacuole (pansporoblast) membrane, and host cell hypertrophy. Spores are ellipsoid and measure 3.1-3.2 × 1.2-1.4, with a coiled polar filament in a single row of 5-6 turns about 52 µm in length.

Methods of control

Remove infected crabs and destroy them such that the tissues do not return to the marine environment. Freezing does not necessarily destroy the spores. Disinfect associated equipment.


Azevedo, C. 1987. Fine structure of the microsporidan Abelspora portucalensis gen. n., sp.n. (Microsporida) parasite of the hepatopancreas of Carcinus maenas (Crustacea, Decapoda). Journal of Invertebrate Pathology 49: 83-92.

Childers, R.K., P.W. Reno and R.E. Olson. 1996. Prevalence and geographic range of Nadelspora canceri (Microspora) in Dungeness crab Cancer magister. Diseases of Aquatic Organisms 24: 135-142.

Couch, J.A. 1983. Diseases caused by protozoa. In: A.J. Provenzano Jr. (ed.). The Biology of Crustacea. Volume 6, Pathobiology. Academic Press, New York, p. 94-98.

Messick, G.A. and C.J. Sindermann. 1992. Synopsis of principal diseases of the blue crab, Callinectec sapidus. NOAA Technical Memorandum NMFS-F/Nec-88. 24 p.

Olson, R.E., K.L. Tiekotter and P.W. Reno. 1994. Nadelspora canceri n.g., n.sp., an unusual microsporidian parasite of the Dungeness crab, Cancer magister. The Journal of Eukaryotic Microbiology 41: 349-359.

Olson, R.E. 1997. Nadelspora canceri, a microsporidian pathogen of the Dungeness crab, Cancer magister. 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. 160.

Overstreet, R.M. 1988. Microsporosis of blue crabs. In: C.J. Sindermann and D.V. Lightner (eds.). Disease Diagnosis and Control in North American Aquaculture. Developments in Aquaculture and Fisheries Science 17. Elsevier, Amsterdam, p. 200-203.

Sparks, A.K. 1985. Synopsis of Invertebrate Pathology Exclusive of Insects. Elsevier Science Publishing Co., Amsterdam. p. 278-280.

Citation Information

Bower, S.M. (1999): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Microsporidosis of Crabs.

Date last revised: August 1999
Comments to Susan Bower

Date modified: