CRUSTACEAN BACTERIA
Prokaryotic Intracytoplasmic Inclusions
I. Causative Agent and Disease
Unlike bivalve molluscs, there are fewer reports of prokaryotic intracy- toplasmic inclusion bodies in crusta- ceans of which 13 cases were caused
by rickettsia-like organisms and one other by chlamydia-like bacteria. All infections produced intracytoplasmic inclusions or microcolonies infecting a wide range of tissues in both freshwater and marine crustaceans. The organisms are either confined to the hepatopan- creatic epithelium or are systemic and vary in their significance from mildly
to seriously pathogenic causing cell en- largement with organ and tissue necrosis including demonstrated or suspected mortality. However, in several of these cases other serious pathogens were also present which may have contributed to the mortality and the observed disease syndrome.
II. Host Species
The single documented chlamydia- like agent was reported from a large Dungeness crab mortality in Puget Sound, Washington. Rickettsia-like agents have been reported from crustaceans in the United States from Florida, Hawaii and Washington, and from British Columbia, Canada, France, Sweden, Mexico, Ecuador, Madagascar, China, Malaysia and Australia. Host species have included wild freshwater amphipods and cultured crayfish, at least five wild and cultured species of penaeid shrimp, one species of wild pandalid shrimp, and one cultured and three wild crab species including a 1984 report of one blue king crab from the eastern Bering Sea near St. Lawrence Island. Later studies (1990) in southeast
Alaska reported a similar rickettsial agent infecting one blue and one golden king crab held captive after collection from Glacier Bay and Lynn Canal near Haines, Alaska.
III. Clinical Signs
Clinical signs vary from normal in appearance to lethargy with mortality and tissue discolorations. King crabs infected by rickettsial organisms may have arrested ovarian development, become lethargic and die when held
for prolonged periods of time. Infected tissues in king crabs have included the epithelial cells of the antennal gland and hepatopancreas that become indurated and friable. Histological examination of infected tissues demonstrates enlarged cells with intracytoplasmic inclusions composed of microcolonies of rod- shaped bacteria causing disseminated granulomatous foci and caseous necrosis of the tissues.
IV. Transmission
Certain rickettsia-like organisms
in cultured and wild shrimp have been transmitted horizontally by cannibalism and via seawater exposure. Similar stud- ies with other rickettsias either have not been successful or the mode of transmis- sion is unknown.
V. Diagnosis
Histological examination of infected tissues reveal the typical enlarged cells containing microcolonies of organisms. Confirmation of typical rickettsial orchlamydial morphology is by transmis- sion electron microscopy. PCR may be available for certain agents described in the literature. None of these agents have
been isolated in culture using conven- tional methods.
VI. PrognosisforHost
Infections can be light and insignifi- cant but low to high mortality has also been reported for both wild and cultured shrimp and crabs.
VII. Human Health Significance
There are no known zoonotic human health concerns regarding infection of crustaceansbythesepoikilothermicor- ganisms which are different from similar organisms causing diseases in higher animals.
Caseous necrosis of hepatopancreas from golden king crab infected with a rickettsia-like organism that has destroyed hepatopancreatic tubules
https://www.adfg.alaska.gov/static/species/disease/pdfs/crustaceandiseases/prokaryotic_intracytoplasmic_inclusions.pdf
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