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| NAS - Nonindigenous Aquatic Species |
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Common Name: Muskie pox
Synonyms and Other Names: muskie pox (known in salmonids as piscirickettsiosis, salmon rickettsia syndrome, salmonid rickettsial septicemia, or SRS)
Taxonomy: available through 
Identification: P. salmonis are aerobic Gram-negative bacteria occurring intracellularly in fish, primarily salmonids. The bacteria are usually coccoid (but sometimes occur in paired rods or in rings), fastidious (with very specific growth requirements), and non-motile (Mauel and Miller 2002; Fryer and Hedrick 2003). P. cf. salmonis bacteria isolated from muskellunge (Esox masquinongy) in Lake St. Clair only occur as curved rods and rings (Michigan DNR 2007).
P. salmonis in salmonids can result in anemia, kidney necrosis, enlarged spleen, hemorrhages, nodules or crater-form lesions in the liver, dark coloration, skin lesions, lack of appetite, anorexia, and lethargic swimming activity. Symptoms vary in different populations and some fish display no external symptoms at all (Mauel and Miller 2002; Fryer and Hedrick 2003; Rise et al. 2004). In Lake St. Clair, infected muskellunge can exhibit red skin lesions (Michigan DNR 2007).
Size: P. salmonis is 0.5-1.5 µm in diameter (Fryer and Hedrick 2003).
Native Range:
Unknown. The geographic range of P. salmonis could be broad. It could be native to marine environments, including parts of the Pacific and Atlantic oceans; however, some of the marine regions in which it now occurs could constitute introductions (Fryer and Hedrick 2003).
Nonindigenous Occurrences: P. cf. salmonis was discovered for the first time in muskellunge in Lake St. Clair in May 2002 (Michigan DNR 2007).
Ecology: P. salmonis survives and replicates asexually through fission in the membrane-bound vacuoles inside the cytoplasm of host fish cells. It can rarely be passed from adult to young and is likely passed more frequently from adult to adult, entering through the skin or gills. It is inactive above 20°C and replication is optimal at 15–18°C. It survives better in saltwater than in freshwater, remaining infective for up to 14 days in the former but quickly becoming unstable in the latter (Smith et al. 1999; Mauel and Miller 2002; Fryer and Hedrick 2003; Larenas et al. 2003; Mauel et al. 2003; Smith et al. 2004).
Organisms that are piscirickettsia-like or rickettsia-like (including all fastidious, intracellular fish pathogens) are labeled PLOs or RLOs (Mauel and Miller 2002). PLOs and RLOs are associated with disease in many fish species. Some PLOs are genetically very similar to P. salmonis; a PLO that is 98% similar to typical P. salmonis has been isolated at 10 m depth in bacterioplankton from the coastal waters of Oregon (Mauel and Fryer 2001).
P. salmonis causes mortality in salmonids, killing millions of hatchery farmed fish each year. As for many diseases that naturally occur in the wild, infection becomes more severe in crowded aquaculture settings. Coho salmon (Oncorhynchus kisutch) are highly susceptible while Atlantic salmon (Salmo salar) are less susceptible. P. salmonis has also been reported in rainbow trout (O. mykiss), cherry salmon (O. masou), chinook salmon (O. tschwaytscha), and pink salmon (O. gorbuscha), and can probably infect all salmonids (Mauel and Fryer 2001; Mauel and Miller 2002; Fryer and Hedrick 2003; Birkbeck et al. 2004; Rise et al. 2004).
In addition to the occurrence in freshwater muskellunge in Lake St. Clair, PLOs and RLOs have also been found in: -blue-eyed plecostomus (Panaque suttoni), a tropical freshwater fish shipped from Columbia to the USA (Khoo et al. 1995); -seabass (Dicentrarchus labrax) in the Mediterranean Sea (Comps et al. 1996; Athanassopoulou et al. 1999; McCarthy et al. 2005); -white sea bass (Atractoscion nobilis) off the coast of southern California (Chen et al. 1999; Arkush et al. 2005; Arkush et al. 2006); -puffers (Tetrodon fahaka) from the Nile River in Egypt (Mauel and Miller 2002); -dragonets (Callionymus lyra) from coastal Wales (Mauel and Miller 2002); -tilapia (Oreochromis mossambicus and Sarotherodon melanotheron) in Taiwan, Jamaica, Indonesia, Florida, California, and Hawaii (Chern and Chao 1994; Mauel and Miller 2002); -and in groupers (Epinephelus melanostigma) in Taiwan (Chen et al. 2000).
P. salmonis was not isolated from salmonids in the freshwater stage of their life cycle until 1993 in Chile. The disease was very similar to P. salmonis occurring in fish held in marine aquaculture pens. It could have been transmitted to the fish being cultured in freshwater from brood stock that had survived an outbreak of P. salmonis in a marine environment, or it could have already been present in the freshwater culture environment (Gaggero et al. 1995). The PLO infection of muskellunge in Lake St. Clair is unique, given that it occurred in wild fish. Other fish affected by P. salmonis and PLOs or RLOs have typically been cultured and many have been species that spend at least part of their life cycle in marine environments.
Means of Introduction: Unknown
Status: Unknown
Impact of Introduction:
A) Realised: Diseased muskellunge caught in Lake St. Clair display visible skin rashes. To date there are no significant negative impacts to the muskellunge fishery (Michigan DNR 2007).
B) Potential: P. salmonis causes particularly severe problems for Chilean aquaculture. Many large mortality events occurred starting around 1989 (Larenas et al. 2003; Reid et al. 2004). Chilean aquaculture now raises more Atlantic salmon than coho salmon because the former is more resilient to the disease (Fryer and Hedrick 2003). Mortality events amongst various salmonid species in aquaculture facilities in different countries (i.e. Scotland, Norway, and Canada) have also occurred within the past two decades (Reid et al. 2004). Mortality events caused by PLOs and RLOs in some of the fish species listed above have also occurred, typically in association with aquaculture operations around the world.
Remarks:
References
Arkush, K. D., A. M. McBride, H. L. Mendonca, M. S.Okihiro, K. B. Andree, S. Marshall, V. Henriquez, and R. P. Hedrick. 2005. Genetic characterization and experimental pathogenesis of Piscirickettsia salmonis isolated from white seabass Atractoscion nobilis. Diseases of Aquatic Organisms 63(2-3):139-149.
Arkush, K. D., H. L. Edes, A. M. McBride, M. A. Adkison, and R. P. Hedrick. 2006. Persistence of Piscirickettsia salmonis and detection of serum antibodies to the bacterium in white seabass Atractoscion nobilis following experimental exposure. Diseases of Aquatic Organisms 73(2):131-139.
Athanassopoulou, F., O. Sabatakou, D. Groman, and T. Prapas. 1999. First incidence of rickettsia-like infections in cultured seabass (Dicentrarchus labrax L.) in Greece. Proceedings of the Ninth International Conference, European Association of Fish Pathologists, Rhodes, Greece, September 14-19, 1999.
Birkbeck, T. H., S. Rennie, D. Hunter, L. Laidler, and S. Wadsworth. 2004. Infectivity of a Scottish isolate of Piscirickettsia salmonis for Atlantic salmon Salmo salar and immune response of salmon to this agent. Diseases of Aquatic Organisms 60(2):97-103.
Chen, M. F., J. A. Apperson, T. Gunther, M. L. House, D. B. Antonio, K. B. Andree, S. Z. Yn, M. A. Adkison, G. D. Marty, and R. P. Hedrick. 1999. Isolation and partial characterization of a rickettsia associated with large scale mortality of cultured white seabass (Atractoscion nobilis) in California. Proceedings of the American Fisheries Society/Fish Health Section, 1999 Annual Meeting and Western Fish Disease Workshop, Twin Falls, Idaho, June 9 – 11, 1999.
Chen, S. C., P. C. Wang, M. C. Tung, K. D. Thompson, and A. Adams. 2000. A Piscirickettsia-like organism in grouper, Epinephelus melanostigma, in Taiwan. Journal of Fish Diseases 23:415-418.
Chern, R. S. and C. B. Chao. 1994. Outbreaks of a disease caused by rickettsia-like organism in cultured tilapias in Taiwan. Fish Pathology 29:61-71.
Comps, M., J. C. Raymond, and G. N. Plassiart. 1996. Rickettsia-like organism infecting juvenile sea-bass Dicentrarchus labrax. Bulletin of the European Association of Fish Pathologists 16:30-33.
Fryer, J. L., C. N. Lannan, S. J. Giovannoni, and N. D. Wood. 1992. Piscirickettsia salmonis new genus new species, the causative agent of an epizootic disease in salmonid fishes. International Journal of Systematic Bacteriology 42(1):120-126.
Fryer, J. L. and R. P. Hedrick. 2003. Piscirickettsia salmonis: a Gram-negative intracellular bacterial pathogen of fish. Journal of Fish Diseases 26(5):251-262.
Gaggero, A., H. Castro, and A. M. Sandino. 1995. First isolation of Piscirickettsia salmonis from coho salmons, Oncorhynchus kisutch (Walbaum), and rainbow trout, Oncorhynchus mykiss (Walbaum), during the freshwater stage of their life cycle. Journal of Fish Diseases 18:277-279.
Khoo, L., P. M. Dennis, and G. A. Lewbart. 1995. Rickettsia-like organisms in the blue-eyed plecostomus, Panaque suttoni (Eigenmann and Eigenmann). Journal of Fish Diseases 18:157-164.
Larenas, J. J., J. Bartholomew, O. Troncoso, S. Fernandez, H. Ledezma, N. Sandoval, P. Vera, J. Contreras, and P. Smith. 2003. Experimental vertical transmission of Piscirickettsia salmonis and in vitro study of attachment and mode of entrance into the fish ovum. Diseases of Aquatic Organisms 56(1):25-30.
Mauel, M. J. and D. L. Miller. 2002. Piscirickettsiosis and piscirickettsiosis-like infections in fish: a review. Veterinary Microbiology 87(4):279-289.
Mauel, M. J. and J. L. Fryer. 2001. Amplification of a Piscirickettsia salmonis-like 16S rDNA product from bacterioplankton DNA collected from the coastal waters of Oregon, USA. Journal of Aquatic Animal Health 13(3):280-284.
Mauel, M. J., D. L. Miller, K. Frazier, A. D. Liggett, L. Styer, D. Montgomery-Rock, and J. Brock. 2003. Characterization of piscirickettsiosis-like disease in Hawaiian tilapia. Diseases of Aquatic Organisms 53(3):249-255.
McCarthy, U., N. A. Steiropoulos, K. D. Thompson, A. Adams, A. E. Ellis, and H. W. Ferguson. 2005. Confirmation of Piscirickettsia salmonis as a pathogen in European sea bass Dicentrarchus labrax and phylogenetic comparison with salmonid strains. Diseases of Aquatic Organisms 64(2):107-119. Michigan Department of Natural Resources (DNR). 2007. Muskie pox (Piscirickettsia) fact sheet.
Reid, H. I., A. A. Griffen, and T. H. Birkbeck. 2004. Isolates of Piscirickettsia salmonis from Scotland and Ireland show evidence of clonal diversity. Applied and Environmental Microbiology 70(7):4393-4397.
Rise, M. L., S. R. M. Jones, G. D. Brown, K. R. von Schalburg, W. S. Davidson, and B. F. Koop. 2004. Microarray analyses identify molecular biomarkers of Atlantic salmon macrophage and hematopoietic kidney response to Piscirickettsia salmonis infection. Physiological Genomics 20(1):21-35.
Smith, P. A., M. E. Rojas, A. Guagardo, J. Contreras, M. A. Morales, and J. Larenas. 2004. Experimental infection of coho salmon Oncorhynchus kisutch by exposure of skin, gills and intestine with Piscirickettsia salmonis. Diseases of Aquatic Organisms 61(1-2):53-57.
Smith, P. A., P. Pizarro, P. Ojeda, J. Contreras, S. Oyanedel, and J. Larenas. 1999. Routes of entry of Piscirickettsia salmonis in rainbow trout Oncorhynchus mykiss. Diseases of Aquatic Organisms 37(3):165-172.
Author: Rebekah M. Kipp
Contributing Agencies: 
NOAA - GLERL
Revision Date: 6/12/2007 Citation for this information:
Rebekah M. Kipp. 2009. Piscirickettsia cf. salmonis. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=2658> Revision Date: 6/12/2007
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