Trematode Metacercariae of Crabs
Category 4 (Negligible Regulatory Significance in Canada)
Common, generally accepted names of the organism or disease agent
Metacercarial infection of crabs.
Scientific name or taxonomic affiliation
Various species of Digenea including Microphallus spp., Megalophallus spp.
Global, although each species probably has a confined distribution.
Impact on the host
Majority of the species are innocuous. However, very heavy infections may result in lysis of host muscle tissue surrounding the parasite and ataxia by species that encyst in the nervous system. Hyperparasitism by the haplosporidian Urosporidium crescens causes the larval fluke to become enlarged (0.4-0.6 mm in diameter) and darkly pigmented resulting in the condition called buckshot, pepper spots, or pepper crabs and decreased marketability.
Gross Observations: Invisible to the unaided eye unless hyperparasitized by U. crescens.
Squash Preparations: Metacercaria can be observed in thin slices (about 3 mm thick) of tissue pressed between two glass plates and examined under a dissecting microscope (50 × magnification).
Histology: Cross sections of metacercariae can be observed in stained tissue sections.
Methods of control
Prevention and control impractical.
Messick, G.A. and C.J. Sindermann. 1992. Synopsis of principal diseases of the blue crab, Callinectes sapidus. NOAA Technical Memorandum NMFS-F/Nec-88. 24 p.
Sparks, A.K. 1985. Synopsis of Invertebrate Pathology Exclusive of Insects. Elsevier Science Publishing Co., Amsterdam. p. 352-353.
Bower, S.M., McGladdery, S.E., Price, I.M. (1994): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Trematode Metacercariae of Crabs.
Date last revised: Fall 1994
Comments to Susan Bower
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