Viral Diseases of Crabs

On this page

• Category
• Common, generally accepted names of the organism or disease agent
• Scientific name or taxonomic affiliation
• Geographic distribution
• Host species
• Impact on the host
• Diagnostic techniques
• Methods of control
• References
• Citation information

Category

Category 1 (Not Reported in Canada)

Common, generally accepted names of the organism or disease agent

1. Bi-facies virus (BFV) (=Herpes-like virus disease (HLV)), Reo-like virus disease (RLV) always found with Rhabdo-like virus "A" (RhVA), Picorna-like virus (CBV = Chesapeake Bay virus), Rhabdo-like enveloped helical virus (EHV and RV-CM), Baculoviruses A and B, Subgroup C non-occluded baculovirus (Tau), Parvovirus (PC84), Haemocytopenic Bunyaviridae (CHV).
2. "Herpes-like" Hexagonal nuclear virus, non-occluded baculovirus (Baculo-PP).

Scientific name or taxonomic affiliation

Various viruses as listed above.

Geographic distribution

1. East coast of the United States and the coast of France, but some species may have wider distributions. The occurrence of these viruses in crabs from Canada is not known.
2. Alaska, USA, waters over a wide geographic range.

Host species

1. Callinectes sapidus, Carcinus maenas, Carcinus mediterraneus, Macropipus depurator and some viruses probably occur in other species of crabs.
2. Paralithodes platypus, Paralithodes camtschatica, Lithodes aequispina.

Impact on the hostt

Depending on the virus involved and whether or not there is synergism with other viruses, the effects on the host may be lethal, relatively benign or even unknown. Some viral infections may become patent only when crabs have been exposed to stress factors such as captivity, crowding, or a degraded environment. Viruses considered to be lethal are:

1. BFV - haemolymph fails to clot and is chalky white due to virus particles and haemocyte lysis with death due to haemocyte dysfunction;
2. RLV - death due to nerve and haemocyte dysfunction;
3. CBV - causes destruction of epithelium of bladder, epidermis, gill, gut, and neurosecretory cells of central nervous system and may produce blindness;
4. Tau - lesions limited to the hepatopancreas where epithelial cells are destroyed;
5. "Herpes-like" virus - extensive distruction of bladder and antennal gland.

Diagnostic techniques

Gross Observations

1. BFV - just before death crabs become inactive and withdrawn haemolymph is milky and clots improperly;
2. RLV - slowness, paralysis, and withdrawn haemolymph does not clot completely;
3. CBV - abnormal behaviour and blindness;
4. Tau - decreased aggressive behaviour, increased lethargy, loss of appetite, followed within a few days by death;
5. "Herpes-like" virus - gross lesions and disease signs have not been reported.

Histology

1. BFV - infected haemocytes and fixed phagocytes contain refractile cytoplasmic inclusions and hypertrophied nuclei with Feulgen positive granules or nuclei stain faintly to deeply Feulgen positive;
2. RLV - cytoplasmic inclusions of paracrystalline arrays that stain Feulgen negative and increased cytoplasmic volume in haemocytes, haematopoietic tissue and glial nerves;
3. CBV - cells hypertrophied, cytoplasm of epithelium of bladder, epidermis, gill, gut and nerve cells filled with Feulgen negative viral material, but infections are usually focal although may be diffuse in certain organs with massive distruction of gill epithelium or retina;
4. Tau - marked nuclear hypertrophy, loss of nucleoli, chromatin margination and karyolysis of all hepatopancreas epithelial cell types and the midgut epithelium;
5. "Herpes-like" virus - parenchymal cells have hypertophied nuclei, chromatin margination and eosinophilic ground substance or inclusion bodies.

Methods of control

Some diseases may be avoided or severity reduced by minimizing stress in captive crabs.

References

Anderson, I.G. and H.C. Prior. 1992. Baculovirus infections in the mud crab, Scylla serrata and a freshwater crayfish, Cherax quadricarinatus, from Australia. Journal of Invertebrate Pathology 60: 265-273.

Brock, J.A. and D.V. Lightner. 1990. Diseases of Crustacea. Diseases caused by microorganisms. In: O. Kinne (ed.). Diseases of Marine Animals. Volume III: Introduction, Cephalopoda, Annelida, Crustacea, Chaetognatha, Echinodermata, Urochordata. Biologische Anstalt Helgoland, Hamburg, p. 260-291.

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.

Citation Information

Bower, S.M., McGladdery, S.E., Price, I.M. (1994): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Viral Diseases of Crabs.

Date last revised: Fall 1994
Comments to Susan Bower