Kudoa thrysites is a myxosporea

Myxosporea

The Myxosporea are a class of microscopic parasites, belonging to the Myxozoa. They have a complex life cycle which comprises vegetative forms in two hosts, an aquatic invertebrate and an ectothermic vertebrate, usually a fish. Each host releases a different type of spore...

n parasite of marine

Ocean

An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

 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. It has a worldwide distribution, and infects a wide range of host species. This parasite is responsible for causing economic losses to the fisheries sector, by causing post-mortem "myoliquefaction", a softening of the flesh to such an extent that the fish becomes unmarketable. It is not infective to humans.

Taxonomy

The spores of K. thyrsites are stella

Stella

-People:*Stella , a feminine given name** Stella McCartney, English fashion designer** Stella , Singaporean-Taiwanese singer** Stella Maessen, Dutch singer, sometimes going under the singular name of Stella-Fictional characters:...

te in shape, with 4 valves and 4 polar capsule

Polar capsule

Polar capsules are structures found in the valves of Myxosporean parasites, which contain the polar filament. The polar capsule is constructed of a proteinaceous and a polysaccharide layer, both layers of which continue into the polar filament....

s. Upon infection by the actinosporean stage the sporoplasm migrates to a muscle fibre where it forms a pseudocyst

Pseudocyst

Pseudocysts are like cysts, but lack epithelial or endothelial cells. Initial management consists of general supportive care. Symptoms and complications caused by pseudocysts require surgery. CT scans are used for initial imaging of cysts, and endoscopic ultrasounds are used in differentiating...

. Within these pseudocysts are the developing spore stages.
Comparison of 18S rDNA sequences of Kudoa species and other myxozoan species to determine their relationships. They show that Kudoa species are distinct from other myxozoans analyzed (Myxidium sp., Myxobolus

Myxobolus

Myxobolus is a genus of myxozoa that includes important parasites of fish like Myxobolus cerebralis. The genus is polyphyletic, with members scattered throughout the myxozoa. Some stages of Myxobolus species were previously thought to be different organisms entirely, but are now united in this group....

 sp., and Henneguya zschokkei

Henneguya zschokkei

Henneguya zschokkei is species of a myxosporean parasite of certain species of salmons of genus Oncorhynchus.Synonyms:* Henneguya salminicola Ward, 1919Hosts:* Oncorhynchus nerka* Oncorhynchus keta* Oncorhynchus tshawytscha...

).
Kudoa thyrsites is an interesting member of this group in that apparently has very broad host specificity, infecting many fish species around the world (Table 1).

Pathology

Members of the genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Kudoa primarily infect muscle

Muscle

Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

 tissue of marine fishes, where they form nodules or pseudocysts containing a great number of individual spores. In lighter infections these pseudocysts are isolated from the fish's immune system

Immune system

An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...

 within the muscle fibre. More intense infections can result in severe inflammation

Inflammation

Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...

 surrounding infected muscle fibres. Although apparently asymptomatic in all but heavy infections, they are associated with post-mortem degeneration of the tissue. This softening of flesh is most likely a result the release of proteolytic enzymes by the parasite.
This causes losses to both aquaculture

Aquaculture

Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...

 operations, for instance, where 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...

 are being reared in "sea-pens", and to capture fisheries

Wild fisheries of the world

A fishery is an area with an associated fish or aquatic population which is harvested for its commercial value. Fisheries can be marine or freshwater. They can also be wild or farmed. This article is an overview of the habitats occupied by the worlds' wild fisheries, and the human impacts on those...

. Losses are both direct, through the degradation of fish products, and indirectly, through the perception of the consumer

Consumer

Consumer is a broad label for any individuals or households that use goods generated within the economy. The concept of a consumer occurs in different contexts, so that the usage and significance of the term may vary.-Economics and marketing:...

 that fish from a particular area are of a lower quality.
The intensity of K. thyrsites infection is positively correlated with the severity of flesh softening in Atlantic salmon fillets. Softening of flesh always occurred with heavily infected fillets, while lightly infected fillets showed no softening.
Prevention and/or control of K. thyrsites infections is problematic especially in open water netpens. Currently there are no available treatments. One approach to control may be to disrupt the life cycle in some way thereby minimizing the likelihood of infection.

Table 1. Distribution and species infected by Kudoa thrysites

Location	Species	Common name
North America	Merluccius productus	Pacific hake Hake The term hake refers to fish in either of:* family Phycidae of the northern oceans* family Merlucciidae of the southern oceans-Hake fish:...
	Oncorhynchus spp.	Pacific 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...
	Icelinus filamentosus	Threadfin sculpin Sculpin A Sculpin is a fish that belongs to the order Scorpaeniformes, suborder Cottoidei and superfamily Cottoidea, that contains 11 families, 149 genera, and 756 species...
	Ophiodon elongatus	Lingcod Lingcod The lingcod, Ophiodon elongatus, is a fish of the greenling family Hexagrammidae. It is the only extant member of the genus Ophiodon...
	Aulorhychus flavidus	Tube-snout Tube-snout The tube-snouts are a family, the Aulorhynchidae, of fish related to the sticklebacks. There are only two species in the family, each placed in its own genus...
	Salmo salar	Atlantic Salmon Atlantic salmon The Atlantic salmon is a species of fish in the family Salmonidae, which is found in the northern Atlantic Ocean and in rivers that flow into the north Atlantic and the north Pacific....
	Reinhardtius stomias	Arrowtooth Flounder Flounder The flounder is an ocean-dwelling flatfish species that is found in coastal lagoons and estuaries of the Northern Atlantic and Pacific Oceans.-Taxonomy:There are a number of geographical and taxonomical species to which flounder belong.*Western Atlantic...
	Eopsetta jordani	Petrale sole Sole (fish) Sole is a group of flatfish belonging to several families. Generally speaking, they are members of the family Soleidae, but, outside Europe, the name sole is also applied to various other similar flatfish, especially other members of the sole suborder Soleoidei as well as members of the flounder...
	Hippoglossus stenolepis	Pacific halibut Halibut Halibut is a flatfish, genus Hippoglossus, from the family of the right-eye flounders . Other flatfish are also called halibut. The name is derived from haly and butt , for its popularity on Catholic holy days...
	Microstomus pacificus	Dover sole Sole (fish) Sole is a group of flatfish belonging to several families. Generally speaking, they are members of the family Soleidae, but, outside Europe, the name sole is also applied to various other similar flatfish, especially other members of the sole suborder Soleoidei as well as members of the flounder...
	Lepidopsetta bilineatus	Rock sole Sole (fish) Sole is a group of flatfish belonging to several families. Generally speaking, they are members of the family Soleidae, but, outside Europe, the name sole is also applied to various other similar flatfish, especially other members of the sole suborder Soleoidei as well as members of the flounder...
	Platichthys stellatus	Starry flounder Flounder The flounder is an ocean-dwelling flatfish species that is found in coastal lagoons and estuaries of the Northern Atlantic and Pacific Oceans.-Taxonomy:There are a number of geographical and taxonomical species to which flounder belong.*Western Atlantic...
	Parophrys vetula	English sole Sole (fish) Sole is a group of flatfish belonging to several families. Generally speaking, they are members of the family Soleidae, but, outside Europe, the name sole is also applied to various other similar flatfish, especially other members of the sole suborder Soleoidei as well as members of the flounder...
	Theragra chalcogramma	Alaskan pollock Pollock Pollock is the common name used for either of the two species of marine fish in the Pollachius genus. Both P. pollachius and P. virens are commonly referred to as pollock. Other names for P...
	Merluccius capensis	Cape hake Hake The term hake refers to fish in either of:* family Phycidae of the northern oceans* family Merlucciidae of the southern oceans-Hake fish:...
Australia	Engraulis australis	Australian anchovy Anchovy Anchovies are a family of small, common salt-water forage fish. There are 144 species in 17 genera, found in the Atlantic, Indian, and Pacific Oceans. Anchovies are usually classified as an oily fish.-Description:...
	Engraulis japonicus	Japanese anchovy Anchovy Anchovies are a family of small, common salt-water forage fish. There are 144 species in 17 genera, found in the Atlantic, Indian, and Pacific Oceans. Anchovies are usually classified as an oily fish.-Description:...
	Sardinella lemuru	Bali sardinella Sardine Sardines, or pilchards, are several types of small, oily fish related to herrings, family Clupeidae. Sardines are named after the Mediterranean island of Sardinia, around which they were once abundant....
	Sardinops neopilchardus	Australian pilchard Sardine Sardines, or pilchards, are several types of small, oily fish related to herrings, family Clupeidae. Sardines are named after the Mediterranean island of Sardinia, around which they were once abundant....
	Spratelloides delicatulus	Blue sprat Spratelloides delicatulus The Blue sprat, Spratelloides delicatulus, also known as the Delicate round herring or Blueback sprat, is a type of sprat fish of Indo-Pacific distribution....
	Coryphaena hippurus	Mahi Mahi
South Africa	Sardinops ocellatus	South African pilchard Sardine Sardines, or pilchards, are several types of small, oily fish related to herrings, family Clupeidae. Sardines are named after the Mediterranean island of Sardinia, around which they were once abundant....
	Thyrsites atun	Snook Centropomus Centropomus Lacépède, 1802, is a genus of predominantly marine fish in family Centropomidae of order Perciformes. The type species is Centropomus undecimalis, the common snook...
Chile	Paralichthys adspersus	Fine flounder Flounder The flounder is an ocean-dwelling flatfish species that is found in coastal lagoons and estuaries of the Northern Atlantic and Pacific Oceans.-Taxonomy:There are a number of geographical and taxonomical species to which flounder belong.*Western Atlantic...
Japan	Cypselurus sp.	Flying fish
Ireland	Salmo salar	Atlantic Salmon Atlantic salmon The Atlantic salmon is a species of fish in the family Salmonidae, which is found in the northern Atlantic Ocean and in rivers that flow into the north Atlantic and the north Pacific....
	Clupea harengus	Herring Herring Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
Spain	Salmo salar	Atlantic Salmon Atlantic salmon The Atlantic salmon is a species of fish in the family Salmonidae, which is found in the northern Atlantic Ocean and in rivers that flow into the north Atlantic and the north Pacific....
United Kingdom	Scomber scomber	Mackerel Mackerel Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel , enter bays and can be...
	Salmo trutta	Street trout

Life cycle

The myxosporeans have been shown to have complex life cycles using more than one host. Usually a fish and an oligochaete or polychaete

Polychaete

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, and in one case a 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.
The life cycle of K. thrysites is poorly understood. It has been hypothesized that K. thyrsites has an indirect life cycle involving some marine invertebrate. Experiments have shown direct transmission of the marine myxosporean Myxidium leei in sea bream. However, direct transmission of K. thyrsites failed when naive fish were fed fresh myxospores. If K. thyrsites does have an indirect life cycle, the intermediate host has yet to be identified.