Tetracapsuloides bryosalmonae
| 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 |
|
| Synonyms | |
|
PKX Organism |
|
PKX Organism
Tetracapsuloides renicola
Tetracapsula bryosalmonae
Tetracapsuloides bryosalmonae is a myxozoan parasite of salmonid fish. 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.
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 bryozoan, Plumatella fungosa, in 1892, which he described as Myxosporidium bryozoides. Myxozoan infection of bryozoans was not reported again until 1996. Ecological investigations of freshwater bryozoans in North America discovered parasitic sacs of a myxozoan species, freely floating in the body cavities of several bryozoans. Molecular analyses indicated that the 18S rDNA sequences of these sacs were indistinguishable from those of PKX, and the PKX organism was scientifically described as Tetracapsuloides bryosalmonae Canning, Curry, Feist, Longshaw & Okamura 1999, which has been assigned to a new class, the Malacosporea within the phylum Myxozoa. Around the same time, another group described the PKX organism from 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.
T. bryosalmonae has a two-host life cycle, although it is highly unusual among the myxosporea, cycling between freshwater bryozoa and salmonid fish species, 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.
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