Microsporidiosis of Dredge Oysters


Category 3 (Host Not in Canada)

Common, generally accepted names of the organism or disease agent

Microsporidiosis, Microsporidiumosis.

Scientific name or taxonomic affiliation

Unidentified species of Microspora currently placed in the collective group Microsporidium rapuae.

Geographic distribution

Foveaux Strait, New Zealand

Host species

Ostrea chilensis (=Tiostrea chilensis, Ostrea lutaria)

Impact on the host

Induces formation of oval cysts (20-70 µm) in connective tissue surrounding the gut. These cysts, only visible in histology, contain numerous spores surrounded by more or less concentric layers of fibrous elements infiltrated by haemocytes.

Diagnostic techniques

Histology: Cysts, as described above, contain numerous oval and refractive spores (5.2 µm x 2.57 µm in frozen sections and 4.7 µm x 2.39 µm in plastic embedded sections). The spore has a polar cap at the apex with an attached polar filament of 19-22 coils and a single nucleus. Sporogenesis and number of spores per pansporoblast are not known.

Figure 1. Two cysts (arrows) containing numerous spores of the unidentified Microsporidium within the connective tissue of Ostrea chilensis from New Zealand. Image provided by Ben Diggles PhD, DigsFish Services www.digsfish.com, ben@digsfish.com.

Methods of control

No known methods of prevention or control.


Jones, J.B. 1981. A new Microsporidium from the oyster Ostrea lurida in New Zealand. Journal of Invertebrate Pathology 38: 67-70.

Sparks, A.K. 1985. Synopsis of Invertebrate Pathology Exclusive of Insects. Elsevier Science Publishing Co., Amsterdam. p. 272.

Citation Information

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

Date last revised: August 2006
Comments to Susan Bower

Date modified: