Microsporidosis (Cotton Shrimp Disease) of Shrimp and Prawns


Category 4 (Negligible Regulatory Significance in Canada)

Common, generally accepted names of the organism or disease agent

Cotton shrimp disease, Milk shrimp disease, Roe shrimp, Cooked shrimp.

Scientific name or taxonomic affiliation

Agmasoma (=Thelohania) spp., Amesoma (=Nosema) spp., Pleistophora (=Plistophora) spp., and Perezia spp.

Geographic distribution

Ubiquitous. Low prevalences in wild shrimp stocks on the west coast of Canada. High prevalance in some cultured stocks of Penaeus merquiensis and Penaeus monodon on the southwest Gulf of Thailand.

Host species

Many species of shrimp and prawns as well as most other marine crustacea such as lobsters and crabs. Microsporida also occur in freshwater crustaceans such as crayfish.

Impact on the host

Microsporidia invade and replace host tissue such as muscle, heart, gonads, gills, hepatopancreas, and nerve ganglia, depending on species. May cause low level mortalities. Infection often causes the shrimp to have a whitish colour making the product unmarketable.

Diagnostic techniques

Gross Observations: Heavy microsporida infections of the muscle tissues cause the muscle to become opaque and the shrimp appear cooked although they are still alive.

Squash Preparations: Microsporidian spores in muscle (also visible if Giemsa stained). Identification to genus and species is based on spore size, shape and number of spores per sporont.

DNA Probes: The chromosomal DNA regions of the SSU rDNA gene of microsporidian isolates (Agmasoma sp.) from P. merquiensis and P. monodon were identical for 722 base pairs suggesting that a single parasite species infects both species of penaeid shrimp (Pasharawipas et al. 1994).

Methods of control

No known methods of prevention or control. Exclude intermediate conditioning hosts (finfish) from ponds. Disinfect ponds.


Clotilde-Ba, F.-L. and B.S. Toguebaye. 1995. Occurrence of microsporidia and gregarines in the shrimp Penaeus notialis from Senegal (West Africa). Bulletin of the European Association of Fish Pathologists 15: 122-124.

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

Flegel, T.W., D.F. Fegan, S. Kongsom, S. Vuthikomudomkit, S. Sriurairatana, S. Boonyaratpalin, C. Chantanachookhin, J.E. Vickers and O.D. Macdonald. 1992. Occurrence, diagnosis and treatment of shrimp diseases in Thailand. In: W. Fulks and K.L. Main (eds.). Diseases of Cultured Penaeid Shrimp in Asia and the United States. The Oceanic Institute, Honolulu, p. 57-112.

Johnston, L.B., S.H. Vernick and V. Sprague. 1978. Light and electron microscope study of a new species of Thelohania (Microsporida) in the shrimp Pandalus jordani. Journal of Invertebrate Pathology 32: 278-290.

Lightner, D.V. 1988. Cotton shrimp disease of penaeid shrimp. In: C.J. Sindermann and D.V. Lightner, (eds.). Disease Diagnosis and Control in North American Marine Aquaculture. Developments in Aquaculture and Fisheries Science 17. Elsevier, Amsterdam, p. 70-75.

Pasharawipas, T., T.W. Flegel, S. Chaiyaroj, S. Mongkolsuk and S. Sirisinha. 1994. Comparison of amplified RNA gene sequences from microsporidian parasites (Agmasoma or Thelohania) in Penaeus merguiensis and P. monodon. Asian Fisheries Science 7: 169-178.

Sparks, A.K. 1985. Synopsis of Invertebrate Pathology Exclusive of Insects. Elsevier Science Publishing Co., Amsterdam. p. 274-278.

Sprague, V. 1970. Some protozoan parasites and hyperparasites in marine decapod Crustacea. American Fisheries Society Special Publication 5: 416-430.

Citation Information

Bower, S.M. (2002): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Microsporidosis (Cotton Shrimp Disease).

Date last revised: April 2002
Comments to Susan Bower

Date modified: