Tetracapsuloides bryosalmonae
Encyclopedia
Tetracapsuloides bryosalmonae is a myxozoa
n parasite of salmon
id fish
es, which 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.
Korotneff observed a myxozoan in the bryozoa
n, Plumatella fungosa, in 1892, which he described as Myxosporidium bryozoides. Myxozoan infection of bryozoans were 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
.
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.
and spleen
, bloody ascites
, and pale gill
s, 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.
composed of all North American sequences plus a subset of Italian and French sequences. High genetic diversity in North America and the absence of genotype
s 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
.
Myxozoa
The Myxozoa are a group of parasitic animals of aquatic environments. Over 1300 species have been described and many have a two-host lifecycle, involving a fish and an annelid worm or bryozoan. The average size of a Myxosporea spore usually ranges from 10 μm to 20 μm and Malacosporea up...
n parasite of salmon
Salmon
Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...
id fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
es, which 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
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 bryozoa
Bryozoa
The Bryozoa, also known as Ectoprocta or commonly as moss animals, are a phylum of aquatic invertebrate animals. Typically about long, they are filter feeders that sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia...
n, Plumatella fungosa, in 1892, which he described as Myxosporidium bryozoides. Myxozoan infection of bryozoans were not reported again until 1996. Ecological investigations of freshwater bryozoans in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
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
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
, the Malacosporea within the phylum Myxozoa
Myxozoa
The Myxozoa are a group of parasitic animals of aquatic environments. Over 1300 species have been described and many have a two-host lifecycle, involving a fish and an annelid worm or bryozoan. The average size of a Myxosporea spore usually ranges from 10 μm to 20 μm and Malacosporea up...
. Around the same time, another group described the PKX organism from Arctic char
Arctic char
Arctic char or Arctic charr is both a freshwater and saltwater fish in the Salmonidae family, native to Arctic, sub-Arctic and alpine lakes and coastal waters. No other freshwater fish is found as far north. It is the only species of fish in Lake Hazen, on Ellesmere Island in the Canadian Arctic...
, 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
Binomial nomenclature
Binomial nomenclature is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages...
.
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 polychaetePolychaete
The Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000...
worm
Worm
The term worm refers to an obsolete taxon used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old English word wyrm. Currently it is used to describe many different distantly-related animals that typically have a long cylindrical...
. 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.
Pathology
Proliferative Kidney Disease is characterised by a swollen kidneyKidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
and spleen
Spleen
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...
, bloody ascites
Ascites
Ascites is a gastroenterological term for an accumulation of fluid in the peritoneal cavity.The medical condition is also known as peritoneal cavity fluid, peritoneal fluid excess, hydroperitoneum or more archaically as abdominal dropsy. Although most commonly due to cirrhosis and severe liver...
, and pale gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s, which indicate the fish is anaemic
Anemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
. Note that these symptoms are common amongst many diseases of fish and do not specifically indicate an infection with Tetracapsuloides bryosalmonae.
Distribution
T. bryosalmonae has been recorded in Europe and North America. Phylogenetic analyses of internal transcribed spacer 1 sequences revealed a cladeClade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
composed of all North American sequences plus a subset of Italian and French sequences. High genetic diversity in North America and the absence of genotype
Genotype
The genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...
s 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
Myxobolus cerebralis
Myxobolus cerebralis is a myxosporean parasite of salmonids that causes whirling disease in farmed salmon and trout and also in wild fish populations...
and Ceratomyxa shasta
Ceratomyxa shasta
Ceratomyxa shasta is a myxosporean parasite that infects salmonid fish on the Pacific coast of North America. It was first observed at the Crystal Lake Hatchery, Shasta County, California, and has now been reported from Idaho, Oregon, Washington, British Columbia and Alaska .-Life history:In...
.