Microsporidiosis of Crayfish


Category 1 (Not Reported in Canada)

Common, generally accepted names of the organism or disease agent

Porcelin disease, Cotton disease, Milky disease, White tail, Protozoan disease, Microsporidan disease, Thelohaniasis of crayfish.

Scientific name or taxonomic affiliation

Various microsporidians including Thelohania contejeani, Thelohania spp., Pleistophora spp., Vavraia parastacida and possibly Nosema sp (identified as a microsporidian with a single spore in each sporophorous vesicle (pansporoblast) from 7 of 106 Austropotamobius pallipes from the Wootten region, England by Pixell Goodrich 1956). Generally, the taxonomy of crayfish microsporidians is obscure which makes it difficult to determine which species have been described from different regions (Edgerton et al. 2002).

Geographic distribution

Eurasia, New Zealand and Australia, with a few reports from the United States.

Host species

Astacus astacus, Austropotamobius pallipes, Cambarellus shufeldi, Cambarus bartoni, Astacus (=Potamobius) pallipes, Cherax quadricarinatus, Cherax destructor, Cherax tenuimanus, Cherax albidus, Pacifastacus leniusculus and other species. Disease status of crayfish in Canada has yet to be determined. Microsporidia also occur in marine crustaceans including lobsters, crabs, shrimp and prawns.

Impact on the host

Generally the prevalence is less than 5% but there have been occasional reports of prevalence up to 30% (Evans and Edgerton 2002). In crayfish with thelohaniasis, the muscle tissue is progressively invaded leading to deterioration of muscle function and death. Thelohaniasis has been attributed as a cause of epidemics among crayfish in Europe. The life cycles of microsporidians in crayfish are poorly understood and may involve intermediate or transport hosts. However, V. parastacida can be directly transmitted between crayfish by cannibalism (Evans and Edgerton 2002). Although C. tenuimanus and C. albidus had a vigorous haemocytic response to infection with V. parastacida, the response appeared confined to areas where the spore mass breached the sarcolemma and failed to arrest progress of the diseases which was more severe in C. albidus (Langdon and Thorne 1992). Microsporidiosis has been described as the most significant disease threat to freshwater crayfish aquaculture in Australia and considered a serious threat to crayfish globally. However, Edgerton and Owens (1999) indicated that it was not a threat to the semi-intensive aquaculture of C. quadricarinatus in northern Queensland, Australia. Microsporidiosis is always fatal though the disease is usually prolonged (Evans and Edgerton 2002).

Diagnostic techniques

Gross Observations: Difficult to detect in early stages, but musculature visible through joints in the abdomen becomes white and opaque (instead of translucent) as the infection progresses in microsporidiosis. Crayfish in a late stage of infection are lethargic and anorexic (Evans and Edgerton 2002).

Wet Mounts: Confirmation of microsporidiosis by microscopic examination of white opaque tissues for an abundance of ovoid spores about 3 to 5 µm in length.

Histology: Clusters of spores within infected tissues. Although the spores are contained within sporophorous vesicles (pansporoblasts) for all infections detected in crayfish to date, the membrane that makes up the sporophorous vesicle may not be evident in histological sections. Thelohania spp. occur mainly in muscle tissue and sporophorous vesicles (roughly spherical and about 5 to 10 µm in diameter) usually containing eight ovoid spores (3.5 x 1.8 µm) that have a clear vacuole at one pole. Vavraia parastacida also occurs in muscle tissue of various organs but mainly in the anterior dorsal tail muscle. Sporophorous vesicles of V. parastacida contain 8, 16, or 32 (rarely 64) ovoid spores (5.5 x 2.6 µm) each with a large prominent posterior vacuole. Pleistophora spp. produce a variable but large number of spores in each sporophorous vesicle. The sporophorous vesicles of unidentified microsporidians in farmed C. quadricarinatus in northern Queensland, Australia, were located in the connective tissues typically near the hepatopancrease and contained spores that were about 4.3 x 2.5 µm in size. These sporophorous vesicles invoked a vigorous haemocytic and significant melanitic response (Edgerton and Owens 1999).

Electron Microscopy: Ultrastructural examination is required for specific identification. Langdon (1991) mentioned ultrastructural features that can be used to differentiate 11 genera of polysporous microsporidians.

Methods of control

Unlikely that treatment could be effective in pond culture. Preventing introduction of the disease is best course.


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Citation Information

Bower, S.M. (2006): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Microsporidiosis of Crayfish.

Date last revised: June 2006
Comments to Susan Bower

Date modified: