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Tetracapsuloides bryosalmonae

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Title: Tetracapsuloides bryosalmonae  
Author: World Heritage Encyclopedia
Language: English
Subject: Salmon, Nanophyetus salmincola, Fish diseases and parasites, Diseases and parasites in salmon, Salmon louse
Collection: Fish Diseases, Kidney Diseases, Myxozoa, Veterinary Parasitology
Publisher: World Heritage Encyclopedia

Tetracapsuloides bryosalmonae

PKX redirects here. For the company, see POSCO.
Tetracapsuloides bryosalmonae
Scientific classification
Kingdom: Animalia
Phylum: Cnidaria
(unranked): Myxozoa
Class: Malacosporea
Order: Malacovalvulida
Family: Saccosporidae
Genus: Tetracapsuloides
Species: T. bryosalmonae
Binomial name
Tetracapsuloides bryosalmonae
Canning et al., 1999

Myxosporidium bryozoides?
Glugea bryozoides?
Nosema bryozoides?
PKX Organism
Tetracapsuloides renicola
Tetracapsula bryosalmonae

Tetracapsuloides bryosalmonae is a myxozoan parasite of salmonid fishes. It causes proliferative kidney disease (PKD), one of the most serious parasitic diseases of salmonid populations in Europe and North America, which causes losses of up to 90% in infected populations.


  • Taxonomy 1
  • Life cycle 2
  • Pathology 3
  • Distribution 4
  • Cited literature 5


Until the late 1990s, the organism which caused PKD was enigmatic. The "PKX organism", the causative agent of the disease, had been recognized as some form of Malacosporean, but the absence of mature spores in salmonid hosts, the lack of fish to fish transmission, and seasonality of the disease suggest that the life cycle of PKX was completed in another host and that infection of salmonids could be accidental. Korotneff observed a myxozoan in the Arctic char, Salvelinus alpinus, as Tetracapsuloides renicola Kent, Khattra, Hedrick & Devlin 2000, but the first given name has priority according to the rules of the binomial nomenclature.

Life cycle

T. bryosalmonae is highly unusual amongst the myxosporea, in that it uses a bryozoan as an alternate host, rather than an oligochaete or polychaete worm. To date, T. bryosalmonae has been found to parasitize five bryozoan species belonging to the genera Fredericella and Plumatella, all considered to be primitive genera. Problems have occurred in determining the fish host for this species. However, recent work has demonstrated that the parasite cycles between bryozoa and native salmonid species.


Proliferative Kidney Disease is characterised by a swollen kidney and spleen, bloody ascites, and pale gills, which indicate the fish is anaemic. Note that these symptoms are common amongst many diseases of fish and do not specifically indicate an infection with Tetracapsuloides bryosalmonae.


T. bryosalmonae has been recorded in Europe and North America. Phylogenetic analyses of internal transcribed spacer 1 sequences revealed a clade composed of all North American sequences plus a subset of Italian and French sequences. High genetic diversity in North America and the absence of genotypes which are characteristic of the North American clade in the rest of Europe implies that southern Europe was colonized by immigration from North America; however, sequence divergence suggests that this colonization substantially pre-dated human movements of fish. Furthermore, the lack of southern European lineages in the rest of Europe, despite widespread rainbow trout farming, indicates that T. bryosalmonae is not transported through fisheries activities. This result contrasts with the commonness of fisheries-related introductions of other pathogens and parasites such as Myxobolus cerebralis and Ceratomyxa shasta.

Cited literature

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