Rickettsia and Chlamydia of Crabs


Category 1 (Not Reported in Canada)

Common, generally accepted names of the organism or disease agent

Rickettsial and Chlamydial infections of crabs.

Scientific name or taxonomic affiliation

  1. Rickettsia-like organism.
  2. Rickettsia-like organism.
  3. Chlamydia-like organism.
  4. Chlamydia-like organism.

Geographic distribution

  1. Sète region on the Mediterranean coast of France.
  2. Bering Sea around Kodiak Island, Alaska, USA.
  3. Puget Sound area of Washington State, USA.
  4. Northeastern coast of the United States.

Host species

  1. Carcinus mediterraneus.
  2. Paralithodes platypus.
  3. Cancer magister.
  4. Cancer irroratus and Cancer borealis.

Impact on the host

  1. Experimental infections by inoculation resulted in death within 15 days. Impact and distribution in wild populations has not been documented.
  2. Infection in one wild caught immature female was massive and apparently caused necrosis and encapsulation of some hepatopancreatic tubules, arrest in ovarian development, and abnormal synchrony in moult cycle. During surveys for pathogens, less developed infections may have been overlooked by light microscopy because the agent is only weakly Feulgen positive. Impact and distribution in wild populations is unknown.
  3. All infections in wild caught crabs were heavy, suggesting a rapid progressive course after infection. Seasonal occurrence of disease was correlated with low water temperatures with a prevalence between 6% and 13% between December and March of 1978 to 1982. It was suggested that this highly pathogenic organism is a significant factor in the health of wild populations of Cancer magister in Puget Sound.
  4. Disease described in laboratory maintained populations where mortality rate was directly proportional to time in captivity. the chlamydia altered the morphology of infected haemocytes and haematopoietic tissue was destroyed in advanced infections.

Diagnostic techniques

Gross Observations:

  1. none reported.
  2. none reported.
  3. Infected crabs were lethargic and haemolymph contained tiny refractile bodies.
  4. none reported.


  1. Feulgen positive microcolonies (10-20 µm in diameter) within intracytoplasmic vacuoles in connective tissue cells of the hepatopancreas, gut, gonad, and gills.
  2. Lightly Feulgen positive microcolonies (10-40 µm diameter) within the cytoplasm of hepatopancreas epithelium.
  3. Massive systemic infections of mesodermal and ectodermal cells (especially fixed tissue phagocytes) that become hypertrophied due to heavy intracellular proliferation of the organism. Cell necrosis and moderate to dense accumulations of haemocytes accompany the chlamydial infections in some tissues.
  4. Swollen haemocytes and haematopoietic cells containing fine basophilic microorganisms that compressed and displaced the nucleus and cytoplasmic organelles to the periphery of the cell.

Electron Microscopy:

  1. Rickettsia-like organisms (2 × 0.7 µm) with plasma membrane and cell wall and contains ribosomes, fibrils and nuclear material. Transverse constrictions along the rod-shaped forms is suggestive of multiplication by binary fission.
  2. The rickettsia-like organisms measure 0.3 × 0.6-1.0 µm.
  3. Membrane bound microcolonies displace cytoplasmic organelles. Cells that contain putative condensing forms and elementary bodies are usually devoid of organelles except the nucleus which is emarginated with chromatin condensed along the borders. Cells with reticulate (initial), intermediate and ellipsoidal bodies are less densely packed and, hence contain more cytoplasmic organelles.
  4. Reticulate stages (560 nm long and 475 nm wide), intermediate and condensing stages (422 nm long and 354 nm wide), and elementary bodies (about 214 nm in diameter) occurred in the cytoplasm of infected cells.

Methods of control

No known methods of prevention or control.


Bonami, J.R. and R. Pappalardo. 1980. Rickettsial infection in marine crustacea. Experientia 36: 180-181.

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. 254-258.

Johnson, P.T. 1984. A rickettsia of the blue king crab, Paralithodes platypus. Journal of Invertebrate Pathology 44: 112-113.

Leibovitz, L. 1988. Hematopoietic chlamydiosis of the rock crab (Cancer irroratus) and the jonah crab (Cancer borealis). The Biological Bulletin (Woods Hole, Mass.) 175: 306. (Abstract).

Pappalardo, R. and J.R. Bonami. 1980. Étude histopathologique et ultrastructurale d'une maladie rickettsienne chez le crabe Carcinus mediterraneus Czerniavski (Crustacé, Decapoda). Revue des Travaux de l'Institut des Pêches Maritimes 44: 277-283.

Sparks, A.K., J.F. Morado and J.W. Hawkes. 1985. A systemic microbial disease in the Dungeness crab, Cancer magister, caused by a Chlamydia-like organism. Journal of Invertebrate Pathology 45: 204-217.

Citation Information

Bower, S.M. (1996): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Rickettsia and Chlamydia of Crabs.

Date last revised: September 1996
Comments to Susan Bower

Date modified: