''Perkinsus marinus'' is a species of alveolates belonging to the phylum

Perkinsozoa Perkinsozoa is a proposed phylum of intracellular parasites in the superphylum Alveolata, which was suggested to account for the genus '' Perkinsus'' and other protist species that do not fit into existing Alveolata phyla. Members Members of t ...

.Joseph, S., et al. (2010)
The alveolate ''Perkinsus marinus'': biological insights from EST gene discovery.
''BMC Genomics'' 11(1), 228. It is similar to a

dinoflagellate The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...

. It is known as a prevalent pathogen of oysters, causing massive mortality in oyster populations. The disease it causes is known as dermo or perkinsosis, and is characterized by the degradation of oyster tissues.Bower, S. M
Synopsis of infectious diseases and parasites of commercially exploited shellfish: ''Perkinsus marinus'' ("dermo" disease) of oysters.
Fisheries and Oceans Canada. 2011. The genome of this species has been sequenced. The species originally was named ''

Dermocystidium ''Dermocystidium'' is a genus of cyst-forming, parasitic eukaryotes of fish, which are the causative agents of dermocystidiosis. Taxonomic History The genus ''Dermocystidium'' was described in 1907. It was previously thought to be a genus of fu ...

marinum''.

Taxonomy

''P. marinus'' is a

protozoa Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...

n of the protist superphylum Alveolata, the alveolates. Its phylum, Perkinsozoa, is a relatively new taxon positioned between the

s and the Apicomplexa, and is probably more closely related to the former. ''P. marinus'' is the type species of the genus ''

Perkinsus ''Perkinsus'' is a genus of alveolates in the phylum Perkinsozoa. The genus was erected in 1978 to better treat its type species, ''Perkinsus marinus'', known formerly as ''Dermocystidium marinum''. These are parasitic protozoans that infect mol ...

'', which was erected in 1978. When first identified in 1950, it was mistaken for a fungus.Villalba, A., et al. (2004)
Perkinsosis in molluscs: a review.
''Aquatic Living Resources'' 17(04), 411-32.

Description and life cycle

The protist is about 2 to 4

μm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

long.Sunila, I
Dermo Disease.
Oyster and Clam Diseases. Connecticut Department of Agriculture. The zoospore has two

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

, which it uses to swim in its

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

habitat. It is ingested by its

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County People *Jim Host (born 1937), American businessman * Michel Host ...

, which is often an oyster of the genus '' Crassostrea''. It then becomes a trophozoite, which proliferates in the tissues of the host. ''P. marinus'' often infests the

hemocyte A blood cell, also called a hematopoietic cell, hemocyte, or hematocyte, is a cell produced through hematopoiesis and found mainly in the blood. Major types of blood cells include red blood cells (erythrocytes), white blood cells (leukocytes), a ...

s, cells in the blood of the host, analogous to malaria in vertebrates.Petty, D
''Perkinsus'' Infections of Bivalve Molluscs.
FA178. Fisheries and Aquatic Sciences. Florida Cooperative Extension Service. University of Florida IFAS. Published 2010. It is also often seen in the cells of the

intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans ...

connective tissue Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...

s, digestive glands, and gills. Inside the cell, the trophozoite produces a vacuole that displaces the

cell nucleus The cell nucleus (pl. nuclei; from Latin or , meaning ''kernel'' or ''seed'') is a membrane-bound organelle found in eukaryotic cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, h ...

. The infested cell is referred to as a

signet ring cell In histology, a signet ring cell is a cell with a large vacuole. The malignant type is seen predominantly in carcinomas. Signet ring cells are most frequently associated with stomach cancer, but can arise from any number of tissues including the ...

, because it is spherical and filled with the rounded vacuole, and resembles a signet ring. The mature trophozoite undergoes binary fission and up to 16 immature trophozoites are produced. These stay in the host animal and infest its tissues, or are released into the water in the

feces Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...

or from a dead host. Trophozoites in the water mature and release flagellated zoospores. The most economically important host is the eastern oyster (''Crassostrea virginica''). The parasite is also common in '' C. corteziensis'', and the species '' C. rhizophorae'', '' C. gasar'', and '' C. brasiliana'' are probably susceptible. '' Magallana gigas'' and '' M. ariakensis'' are experimentally susceptible, but may be more resistant. Certain clams such as '' Mya arenaria'' and '' Macoma balthica'' can be infected in experimental situations. In the laboratory, the

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the ...

'' Boonea impressa'' can be infected and then pass the parasite to an oyster host.

Pathology

Perkinsosis' or "dermo" is the disease condition of the oyster. The name "dermo" was coined when the protist was named ''Dermocystidium marinum'', and it is still commonly used. Infested cells are destroyed by the reproducing protist, and many trophozoites are released into the tissues of the host, or into its bloodstream. There, they infest more cells or are excreted or released when the host dies and disintegrates. The infected oyster becomes stressed, its tissues are pale in color, its gamete production is retarded, its growth slows, it becomes emaciated, its

mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

shrivels and pulls away from the shell, and it may develop pockets of

pus Pus is an exudate, typically white-yellow, yellow, or yellow-brown, formed at the site of inflammation during bacterial or fungal infection. An accumulation of pus in an enclosed tissue space is known as an abscess, whereas a visible collection ...

-like fluid.

Lysis Lysis ( ) is the breaking down of the membrane of a cell, often by viral, enzymic, or osmotic (that is, "lytic" ) mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a ''lysate''. In molecular bio ...

of tissues and blockage of blood vessels causes fatality, but many oysters can persist up to 3 years with active infections.

Distribution

The protist occurs along the North American coast from Maine to Florida to the Yucatán Peninsula of Mexico. Dermo epizootic outbreaks occurred in the Gulf of Mexico in the 1940s. Periodic outbreaks in the Chesapeake Bay have caused extensive oyster mortality. Significant disease has occurred in Delaware Bay,

Long Island Sound Long Island Sound is a marine sound and tidal estuary of the Atlantic Ocean. It lies predominantly between the U.S. state of Connecticut to the north and Long Island in New York to the south. From west to east, the sound stretches from the Eas ...

, and other parts of the coast of the northeastern United States. Oyster farming operations have been disrupted in some areas, particularly in Mexico.

Management

The prevalence of the protist and the disease are influenced by environmental factors such as temperature,

salinity Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...

, and food availability to the hosts. Oysters exposed to environmental pollutants such as ''N''-Nitrosodimethylamine, and tributyltins experience more severe disease. At higher temperatures, the chemical defenses of the oyster, particularly its lysozymes, are reduced; infections are more common and more severe in the summer. Warmer winter ocean temperatures also promote outbreaks.Cook, T., et al. (1998)
The relationship between increasing sea-surface temperature and the northward spread of ''Perkinsus marinus'' (dermo) disease epizootics in oysters.
'' Estuarine, Coastal and Shelf Science'' 46(4), 587-97. While laboratory studies of certain

antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of ...

s have been promising, no methods of eradication are effective, so prevention is important. Oysters from populations or farms that have experienced disease should not be moved to areas without infestations, because the protist is easily introduced and transmitted. In

aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...

, efforts to locate and breed more resistant strains of oysters are ongoing. Infested seed oysters should not be planted in oyster beds, and in disease-ridden areas, the oysters should be removed and the site allowed to lie fallow to reduce the protist load.

Taxonomy

Description and life cycle

Pathology

Distribution

Management

See also

References

Further reading