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Taura syndrome (TS) is one of the more devastating diseases affecting the
shrimp farming Shrimp farming is a form of aquaculture that takes place in marine or freshwater environments, producing shrimp or prawns (crustaceans of the groups Caridea or Dendrobranchiata) for human consumption. However, the industry has raised concerns abou ...
industry worldwide. It was first described in
Ecuador Ecuador, officially the Republic of Ecuador, is a country in northwestern South America, bordered by Colombia on the north, Peru on the east and south, and the Pacific Ocean on the west. It also includes the Galápagos Province which contain ...
during the summer of 1992. In March 1993, it returned as a major
epidemic An epidemic (from Greek ἐπί ''epi'' "upon or above" and δῆμος ''demos'' "people") is the rapid spread of disease to a large number of hosts in a given population within a short period of time. For example, in meningococcal infection ...
and was the object of extensive media coverage. Retrospective studies have suggested a case of Taura syndrome might have occurred on a
shrimp farm Shrimp farming is a form of aquaculture that takes place in marine or freshwater environments, producing shrimp or prawns (crustaceans of the groups Caridea or Dendrobranchiata) for human consumption. However, the industry has raised concerns abou ...
in
Colombia Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...
as early as 1990 and the virus was already present in Ecuador in mid-1991. Between 1992 and 1997, the disease spread to all major regions of the Americas where
whiteleg shrimp Whiteleg shrimp (''Litopenaeus vannamei'', synonym ''Penaeus vannamei''), also known as Pacific white shrimp or King prawn, is a species of prawn of the eastern Pacific Ocean commonly caught or farmed for food. Description ''Litopenaeus vannam ...
(''Litopenaeus vannamei'') is cultured. The economic impact of TS in the Americas during that period might have exceeded US$2 billion by some estimates.


Overview

The 1992 Ecuadorian TS epidemic occurred concurrently with an outbreak of black leaf wilt disease in
banana plantations A banana plantation is a commercial agricultural facility found in tropical climates where bananas are grown. Geographic distribution Banana plants may grow with varying degrees of success in diverse climatic conditions, but commercial banana pl ...
. The outbreak of black leaf disease led to an increase in
fungicide Fungicides are pesticides used to kill parasitic fungi or their spores. Fungi can cause serious damage in agriculture, resulting in losses of yield and quality. Fungicides are used both in agriculture and to fight fungal infections in animals, ...
usage within the Taura River basin district near the city of
Guayaquil Guayaquil (), officially Santiago de Guayaquil, is the largest city in Ecuador and also the nation's economic capital and main port. The city is the capital (political), capital of Guayas Province and the seat of Guayaquil Canton. The city is ...
. The fungicides
propiconazole Propiconazole is a triazole fungicide, also known as a DMI, or demethylation inhibiting fungicide due to its binding with and inhibiting the Lanosterol 14 alpha-demethylase, 14-alpha demethylase enzyme from demethylating a precursor to ergosterol. ...
(
Tilt Tilt may refer to: Music * Tilt (American band), a punk rock group, formed in 1992 * Tilt (British band), an electronic music group, formed in 1993 * Tilt (Polish band), a rock band, formed in 1979 Albums * ''Tilt'' (Cozy Powell album), 1981 ...
,
Ciba-Geigy Novartis AG is a Swiss multinational pharmaceutical corporation based in Basel, Switzerland. Novartis is one of the largest pharmaceutical companies in the world and was the eighth largest by revenue in 2024. Novartis manufactures the drugs ...
) and tridemorph ( Calixin,
BASF BASF SE (), an initialism of its original name , is a European Multinational corporation, multinational company and the List of largest chemical producers, largest chemical producer in the world. Its headquarters are located in Ludwigshafen, Ge ...
) used to control black leaf, ran off into nearby ponds and were initially thought to be responsible for the disease. Analytical data demonstrated
propiconazole Propiconazole is a triazole fungicide, also known as a DMI, or demethylation inhibiting fungicide due to its binding with and inhibiting the Lanosterol 14 alpha-demethylase, 14-alpha demethylase enzyme from demethylating a precursor to ergosterol. ...
in water, sediments and
hepatopancreas The hepatopancreas, digestive gland or midgut gland is an organ of the digestive tract of arthropods and molluscs. It provides the functions which in mammals are provided separately by the liver and pancreas, including the production of digestive ...
tissues of shrimp harvested from affected farms in Ecuador. No other pesticides were discovered. In January 1994, at the request of Ciba-Geigy, a workshop on Taura syndrome was held at the Aquaculture Pathology Laboratory of the
University of Arizona The University of Arizona (Arizona, U of A, UArizona, or UA) is a Public university, public Land-grant university, land-grant research university in Tucson, Arizona, United States. Founded in 1885 by the 13th Arizona Territorial Legislature, it ...
. Experts from several countries with expertise in shrimp and insect pathology, shrimp nutrition, toxicology, mycology, water quality and farm management participated in the workshop. Industry representatives also participated. The group developed recommendations as to the standardization of the research on TS and suggested that studies be done to evaluate whether fungicides or as-yet unrecognized agents were responsible for the syndrome. Dr. Jim Brock, the aquatic disease specialist for the State of Hawaii during this period, first demonstrated the disease could be transmitted by feeding Taura victims to healthy shrimp in early 1994. The dying test shrimp were then fed to a new set of shrimp, which was dying at the same rate. Rivers' postulates were fulfilled in 1994 by Dr. Ken Hasson and co-researchers at the University of Arizona. This proved the viral etiology of the syndrome. The virus was named Taura syndrome virus, often referred to as TSV. The virus is referred to by the name infectious cuticular epithelial necrosis virus (ICENV) by some authors in Latin America. Taura syndrome is a notifiable disease by the Office international des Épizooties (OIE), which reflects the serious nature and devastating impact of the disease.


Identification and description of the virus

Taura syndrome virus was first classified as a possible member of the family
Picornaviridae Picornaviruses are a group of related nonenveloped RNA viruses which infect vertebrates including fish, mammals, and birds. They are viruses that represent a large family of small, positive-sense, single-stranded RNA viruses with a 30 nm ...
based on biological and physical characteristics. It was later reclassified in the Dicistroviridae family, genus '' Cripavirus''. It has since been reassigned to a second genus in the same family – the Aparavirus. TSV is a 32  nm nonenveloped particle with an
icosahedral In geometry, an icosahedron ( or ) is a polyhedron with 20 faces. The name comes . The plural can be either "icosahedra" () or "icosahedrons". There are infinitely many non- similar shapes of icosahedra, some of them being more symmetrical tha ...
morphology and a buoyant density of 1.338 g/ml. The genome is single-stranded
positive-sense In molecular biology and genetics, the sense of a nucleic acid molecule, particularly of a strand of DNA or RNA, refers to the nature of the roles of the strand and its complement in specifying a sequence of amino acids. Depending on the context, ...
and has 10,205
nucleotide Nucleotides are Organic compound, organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both o ...
s (excluding the 3' poly-A tail). The
capsid A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or m ...
consists of three major proteins: CP1 (40 kDa), CP2 (55 kDa) and CP3 (24 kDa) alongside a minor protein of 58 kDa. Audelo-del-Valle in 2003 reported certain primate cell lines could be used to culture TSV. Later studies demonstrated their report was based on misinterpreted data. TSV does not appear to be a potential
zoonosis A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a virus, bacterium, parasite, fungi, or prion) that can jump from a non-human vertebrate to a human. When ...
. All virus amplifications require the use of live shrimp, as there is no continuous
cell line An immortalised cell line is a population of cells from a multicellular organism that would normally not proliferate indefinitely but, due to mutation, have evaded normal cellular senescence and instead can keep undergoing division. The cells ...
that supports the growth of shrimp viruses.


Variants of the virus

RNA viruses such as TSV have high rates of
spontaneous mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mitosis ...
. These very high rates might be due to the lack of proofreading function of the
RNA-dependent RNA polymerase RNA-dependent RNA polymerase (RdRp) or RNA replicase is an enzyme that catalyzes the self-replication, replication of RNA from an RNA template. Specifically, it catalyzes synthesis of the RNA strand Complementarity (molecular biology), compleme ...
and have resulted in the emergence of several genetic variants of the virus. As of May 2009, four genetic clusters are recognized:
Belize Belize is a country on the north-eastern coast of Central America. It is bordered by Mexico to the north, the Caribbean Sea to the east, and Guatemala to the west and south. It also shares a maritime boundary with Honduras to the southeast. P ...
(TSV-BZ), America (TSV-HI), Southeast Asia and
Venezuela Venezuela, officially the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and many Federal Dependencies of Venezuela, islands and islets in the Caribbean Sea. It com ...
. The Belize strain is considered the most virulent.
Point mutations A point mutation is a genetic mutation where a single nucleotide base is changed, inserted or deleted from a DNA or RNA sequence of an organism's genome. Point mutations have a variety of effects on the downstream protein product—consequences ...
in TSV
capsid A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or m ...
proteins might provide specific isolates with selective advantages such as host adaptability, increased
virulence Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most cases, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its abili ...
or increased replication ability. Even small variations in the TSV
genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...
can result in substantial differences in
virulence Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most cases, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its abili ...
. All TSV variants are similar in shape and size, with light variations. The average size of TSV-BZ virus particles is 32.693+/- 1.834 nm compared to TSV-HI with a size of 31.485 +/- 1.187 nm. The region of highest genetic difference is within the capsid protein CP2, with
pairwise comparison Pairwise generally means "occurring in pairs" or "two at a time." Pairwise may also refer to: * Pairwise disjoint In set theory in mathematics and Logic#Formal logic, formal logic, two Set (mathematics), sets are said to be disjoint sets if th ...
of nucleotide showing a 0 to 3.5% difference amongst isolates. The most variations in CP2 occur at the 3'-terminal sequence; this may be because it is less constrained by structural requirements and more exposed than other regions of the protein.


Geographic distribution

TSV has been reported from virtually all shrimp-growing regions of the Americas, including Ecuador,
Colombia Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...
,
Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...
,
Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
,
El Salvador El Salvador, officially the Republic of El Salvador, is a country in Central America. It is bordered on the northeast by Honduras, on the northwest by Guatemala, and on the south by the Pacific Ocean. El Salvador's capital and largest city is S ...
,
Guatemala Guatemala, officially the Republic of Guatemala, is a country in Central America. It is bordered to the north and west by Mexico, to the northeast by Belize, to the east by Honduras, and to the southeast by El Salvador. It is hydrologically b ...
,
Honduras Honduras, officially the Republic of Honduras, is a country in Central America. It is bordered to the west by Guatemala, to the southwest by El Salvador, to the southeast by Nicaragua, to the south by the Pacific Ocean at the Gulf of Fonseca, ...
, Belize,
Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...
,
Nicaragua Nicaragua, officially the Republic of Nicaragua, is the geographically largest Sovereign state, country in Central America, comprising . With a population of 7,142,529 as of 2024, it is the third-most populous country in Central America aft ...
,
Panama Panama, officially the Republic of Panama, is a country in Latin America at the southern end of Central America, bordering South America. It is bordered by Costa Rica to the west, Colombia to the southeast, the Caribbean Sea to the north, and ...
,
Costa Rica Costa Rica, officially the Republic of Costa Rica, is a country in Central America. It borders Nicaragua to the north, the Caribbean Sea to the northeast, Panama to the southeast, and the Pacific Ocean to the southwest, as well as Maritime bo ...
, and Venezuela, as well as from the states of Hawaii,
Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...
,
Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...
and
South Carolina South Carolina ( ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders North Carolina to the north and northeast, the Atlantic Ocean to the southeast, and Georgia (U.S. state), Georg ...
. Until 1998, it was considered to be a Western Hemisphere virus. The first Asian outbreak occurred in
Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia. The main geography of Taiwan, island of Taiwan, also known as ''Formosa'', lies between the East China Sea, East and South China Seas in the northwestern Pacific Ocea ...
. It has more recently been identified in
Thailand Thailand, officially the Kingdom of Thailand and historically known as Siam (the official name until 1939), is a country in Southeast Asia on the Mainland Southeast Asia, Indochinese Peninsula. With a population of almost 66 million, it spa ...
,
Myanmar Myanmar, officially the Republic of the Union of Myanmar; and also referred to as Burma (the official English name until 1989), is a country in northwest Southeast Asia. It is the largest country by area in Mainland Southeast Asia and has ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
,
Korea Korea is a peninsular region in East Asia consisting of the Korean Peninsula, Jeju Island, and smaller islands. Since the end of World War II in 1945, it has been politically Division of Korea, divided at or near the 38th parallel north, 3 ...
, and
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...
, where it has been associated with severe epizootics in farmed ''Penaeus vannamei'' and ''Penaeus monodon''. The wide distribution of the disease has been attributed to the movement of infected host stocks for aquaculture purposes. This might have been helped by the highly stable nature of the virus. Importation of TSV-infected ''P. vannamei'' from the Western Hemisphere is thought to have been the origin of the outbreak in Taiwan. This was further suggested by the genomic similarity of the Taiwan and Western Hemisphere isolates. TSV appeared in Thailand in 2003. Due to the similarities in deduced CP2 amino acids sequence and the chronology of the disease outbreaks in relation to imported stocks, at least some of the Thai isolates likely originated from Chinese stocks. Taura syndrome can spread rapidly when introduced in new areas. A shrimp farmer described the 1995 outbreak in Texas as, "This thing spread like a forest fire... There was no stopping it. I just sat there and watched it and in a matter of three days, my shrimp were gone. Dead!"


Species of susceptible shrimp

TSV is known to affect many shrimp species. It causes serious diseases in the postlarval, juvenile and adult stages of ''Penaeus vannamei''. It also affects severely ''P. setiferus'', ''P. stylirostris'', ''P. schmitti'', and ''Metapenaeus ensis''. ''P. chinensis'' is highly susceptible to the disease in experimental
bioassay A bioassay is an analytical method to determine the potency or effect of a substance by its effect on animal testing, living animals or plants (''in vivo''), or on living cells or tissues (''in vitro''). A bioassay can be either quantal or quantit ...
s. Variation occurs within species, and TSV-resistant strains of shrimp have been developed. Wild stocks are showing increased resistance, perhaps through intense natural selection. Reports of TS in the wild are limited, but in February 1995, the Mexican Fisheries Ministry reported the presence of TSV in wild-type shrimp captured on the border of Mexico and Guatemala. As of 2007, no confirmed reports indicated TSV is infectious to other groups of decapod or nondecapod crustaceans.


Pathology and disease cycle

In farm situations, TS often causes high mortality during the first 15 to 40 days of stocking into shrimp ponds. The course of infection may be acute (5–20 days) to chronic (more than 120 days) at the pond and farm level. The disease has three distinct phases that sometimes overlap: acute, transition and chronic. The disease cycle has been characterized in detail in ''P. vannamei''. After the initial infection, the acute phase develops. Clinical signs can occur as early as 7 hours after infection in some individuals and last for about 4–7 days. Infected shrimp display
anorexia Anorexia nervosa (AN), often referred to simply as anorexia, is an eating disorder characterized by Calorie restriction, food restriction, body image disturbance, fear of gaining weight, and an overpowering desire to be thin. Individuals wit ...
,
lethargy Lethargy is a state of tiredness, sleepiness, weariness, fatigue, sluggishness, or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to inadequate sleep, overexertion, overw ...
and erratic swimming behavior. They also present opacification of the tail musculature, soft cuticle and, in naturally occurring infection, a red tail due to the expansion of the red chromatophores. Mortality during this phase can be as high as 95%. The acute phase is characterized histologically by multifocal areas of nuclear pyknosis/karyorrhexis and numerous cytoplasmic inclusion bodies in the cuticular epithelium and the subcutis of the general body surface, all appendages, gills, hindgut, esophagus and stomach. The pyknosis and karyorrhexis give a "buckshot" appearance to the tissue and are considered
pathognomonic Pathognomonic (synonym ''pathognomic'') is a term, often used in medicine, that means "characteristic for a particular disease". A pathognomonic sign is a particular sign whose presence means that a particular disease is present beyond any doubt. ...
for the disease. In severe infections the antennal gland tubule
epithelium Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...
, the hematopoietic tissues and the testis are also affected. This occurs mainly in severe infection following injection of viral particles and has not been reported from naturally infected ''P. vannamei''. Shrimp that survive the acute stage enter a transitional stage. Shrimp in the transitional phase show randomly distributed, melanized (brownish/black) lesions within of the cuticle of the cephalothorax and tail region. These foci are the sites of acute lesions which have progressed onto subsequent stages of hemocytic inflammation, cuticular epithelium regeneration and healing and which might be secondarily infected with bacteria. These foci are negative for TSV by ''in situ'' hybridization (ISH) using a TSV-specific
cDNA In genetics, complementary DNA (cDNA) is DNA that was reverse transcribed (via reverse transcriptase) from an RNA (e.g., messenger RNA or microRNA). cDNA exists in both single-stranded and double-stranded forms and in both natural and engin ...
probe. Histologically, these shrimp present focal active acute lesions and the onset of lymphoid organ spheroids (LOSs) development. By ISH with TSV-specific probes, a diffuse positive signal can be observed within the walls of the lymphoid organ of normal appearance with or without focal probe signals within developing LOSs. These shrimp will be lethargic and anorexic, possibly because of the redirection of their energy and metabolic resources toward wound repair and recovery. If the shrimp undergo another successful
moult In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is a process by which an animal casts off parts of its body to serve some beneficial purpose, either at ...
following the transitional phase, they will cast off the melanized lesions and enter the chronic phase. The chronic phase is first seen six days after infection and persist for at least 12 months under experimental conditions. This phase is characterized histologically by the absence of acute lesions and the presence of LOS of successive morphologies. These LOSs are positive by ISH for TSV. A low prevalence of ectopic spheroids can also be observed in some cases. LOSs are not by themselves characteristic of TSV infection and can be found in other viral diseases of shrimp such as lymphoid organ vacuolization virus (LOVV), lymphoid parvo-like virus (LPV), lymphoid organ virus (LOV), rhabdovirus of penaeid shrimp (RPS) and yellowhead virus (YHV). Diagnosis of the disease during the chronic phase is problematic, as shrimp do not display any outward signs of the disease and do not show mortality from the infection. Survivors may become carriers for life. Shrimp with chronic TSV infection are not as vigorous as uninfected shrimp, as demonstrated by their inability to tolerate a salinity drop as well as uninfected shrimp. A 2011 study by Laxminath Tumburu looked at the relationship between an environmental stressor (pesticide
endosulfan Endosulfan is an organochlorine insecticide and acaricide, which acts by blocking the GABA-gated chloride channel of the insect (Insecticide Resistance Action Committee#Table of modes of action and classes of insecticide, IRAC group 2A). It became ...
) and Taura syndrome virus (TSV) and their interactions on the susceptibility and molting of marine penaeid shrimp ''L. vannamei'' and found the interference of endosulfan-associated stress led to increasingly higher susceptibility at postmolt stage during the acute phase of the TSV disease cycle.


Routes of transmission

The most likely route for transmission of TSV is
cannibalism Cannibalism is the act of consuming another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded in more than 1,500 species. Human cannibalism is also well document ...
of dead infected shrimp. The virus can be spread from one farm to another by seagulls and aquatic insects. Infectious TSV has been found in the feces of
laughing gull The laughing seagull (''Leucophaeus atricilla'') is a medium-sized gull of North America, North and South America. Named for its laugh-like call, it is an opportunistic omnivore and scavenger. It breeds in large colonies mostly along the Atlantic ...
s that fed on infected shrimp during an epizootic in Texas. Controlled laboratory studies have documented that TSV remains infectious for up to one day after passage through the gut of white leghorns chicken ('' Gallus domesticus'') and laughing gulls. Although vertical transmission is suspected this has not been experimentally confirmed. Shrimp surviving a TSV infection are lifelong carriers of the virus and are a significant source of virus for susceptible animals. It has been hypothesized that TSV was introduced to Southeast Asia with chronically infected shrimp imported from the Western Hemisphere. The ability of TSV to remain at least partly infectious after one or several freeze-thaw cycles might be a contributing factor facilitating its spread in the international commerce of frozen commodity products. Mechanisms by which infected frozen shrimp could spread the virus include: reprocessing of shrimp at processing plants with release of infectious liquid wastes, disposal of solid wastes in landfills where seagulls could acquire the virus and then spread it, the use of shrimp as bait by sport fishermen and the use of imported shrimp as fresh food for other aquatic species.


Diagnostic methods

A presumptive diagnosis of acute TSV infection can be established by the presence of dead or dying shrimp in
cast net A casting net, also called a throw net, is a net used for fishing. It is a circular net with small weights distributed around its edge. The net is cast or thrown by hand in such a manner that it spreads out while it's in the air before it sin ...
s used for routine evaluation. Predatory birds are attracted to diseased ponds and feed heavily on the dying shrimp. The unique signs of infection caused by TS, such as the cuticular melanized spots, can provide a strong
presumptive diagnosis Presumptive tests, in medical and forensic science, analyze a sample and establish one of the following: #The sample is definitely not a certain substance. #The sample probably is the substance. For example, the Kastle–Meyer test will show eith ...
, but care must be taken as these can be confused with other diseases, such as bacterial shell disease. In general
pathognomonic Pathognomonic (synonym ''pathognomic'') is a term, often used in medicine, that means "characteristic for a particular disease". A pathognomonic sign is a particular sign whose presence means that a particular disease is present beyond any doubt. ...
histopathological lesions are the first step in confirmatory diagnosis. Discrete foci of pyknotic and karyorhectic nuclei and inflammation are seen within the cuticular tissues. The lymphoid organ might display
spheroids A spheroid, also known as an ellipsoid of revolution or rotational ellipsoid, is a quadric surface (mathematics), surface obtained by Surface of revolution, rotating an ellipse about one of its principal axes; in other words, an ellipsoid with t ...
, but is otherwise unremarkable. The
genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...
of the
virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...
has been cloned and
cDNA In genetics, complementary DNA (cDNA) is DNA that was reverse transcribed (via reverse transcriptase) from an RNA (e.g., messenger RNA or microRNA). cDNA exists in both single-stranded and double-stranded forms and in both natural and engin ...
probes are available for diagnosis. Reverse transcriptase polymerase chain reaction (
RT-PCR Reverse transcription polymerase chain reaction (RT-PCR) is a laboratory technique combining reverse transcription of RNA into DNA (in this context called complementary DNA or cDNA) and amplification of specific DNA targets using polymerase chain ...
) methods have been developed for detection of TSV and are very sensitive. Real-time techniques allow for quantification of the virus. The IQ2000TM TSV detection system, a RT-PCR method, is said to have a detection limit of 10 copies per reaction. RNA-based methods are limited by the relative fragility of the viral RNA. Prolonged fixation i
Davidsons' fixative
might result in RNA degradation due to fixative-induced acid hydrolysis. An alternative for virus detection is the use of specific
monoclonal antibodies A monoclonal antibody (mAb, more rarely called moAb) is an antibody produced from a Lineage (evolution), cell lineage made by cloning a unique white blood cell. All subsequent antibodies derived this way trace back to a unique parent cell. Mon ...
(MAbs) directed against the relatively stable proteins in the viral capsid. Rapid diagnostic tests using MAbs are now in common use for white spot syndrome virus and are being marketed under the commercial name of ''Shrimple''. Similar tests for TSV, yellowhead virus and infectious hypodermal and haematopoietic necrosis virus are currently under development.


Methods of control

Management strategies for the disease have included raising more resistant species such as the Western blue shrimp (''Penaeus stylirostris'') and stocking of
specific pathogen free Specific-pathogen-free (SPF) is a term used for laboratory animals that are guaranteed free of particular pathogens. Use of SPF animals ensures that specified diseases do not interfere with an experiment. For example, absence of respiratory patho ...
(SPF) or specific pathogen resistant (SPR) shrimp. Relatively simple laboratory challenges can be used to predict the performance of selected stocks in farms where TSV is enzootic. The resistant shrimp lines currently raised have reached nearly complete resistance to some TSV variants and further improvement due to breeding for TSV-resistance is expected be minor for these variants. Significant improvements in TSV survival were made through selective breeding despite low to moderate heritability for this trait. A management strategy used to reduce the impact of TS has been the practice of stocking postlarval shrimp at increased stocking density. Following this strategy, farms would experience mortality due to TS at an early stage of the production cycle, before substantial feeding had begun and the surviving shrimp would be resistant to further TSV challenges. Other techniques used with limited efficacy have been the polyculture of shrimp with tilapia and maintenance of near-optimal water quality conditions in the grow-out ponds with reduction of organic loading. Transgenic shrimp expressing an antisense TSV coat protein (TSV-CP) exhibited increased survival in TSV challenges. The public perception of
transgenic A transgene is a gene that has been transferred naturally, or by any of a number of genetic engineering techniques, from one organism to another. The introduction of a transgene, in a process known as transgenesis, has the potential to change the ...
animals, as well as current technical limitations, limit the use of transgenic animals as a mean of disease control.


Notes


References


External links

* {{DEFAULTSORT:Taura Syndrome Animal viral diseases Aquaculture Diseases and parasites of crustaceans Syndromes in crustaceans