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Torovirus
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Torovirus
Torovirus is a genus of enveloped, positive-strand RNA viruses in the order Nidovirales and family Tobaniviridae. They primarily infect vertebrates, especially cattle, pigs, and horses. Diseases associated with this genus include gastroenteritis, which commonly presents in mammals. Torovirus is the only genus in the monotypic subfamily Torovirinae.
The discovery of the first torovirus can be traced back to 1970s. Equine torovirus (EToV) was accidentally found in the rectal sample from a horse who was experiencing severe diarrhea. The 'Breda' bovine torovirus was later found in 1979 while investigation in a dairy farm in Breda. They had several calves experiencing severe diarrhea for months. In 1984, torovirus-like particles were detected with electron microscope (EM) technique in the human patients with gastroenteritis.
Until recently, the toroviruses were not assigned any family. The recent molecular analysis of the virus revealed its similarities with Arterivirus and coronaviruses, which led to the inclusion of the Torovirus along with the Arterivirus in the previously monogeneric Coronaviridae. At present, toroviruses are included in the order Nidovirales sub family Torovirinae, family Tobaniviridae. Resemblance, molecular and genetic similarities, virion dimensions, behavioral ties and other characteristic similarities and differences are observed by the researchers for the taxonomic classification of the virus. In the toroviruses, the Berne virus has been extensively studied at the molecular level as compared to its other members. In 1992, the International Committee on Taxonomy of Viruses ICTV got enough data to consider torovirus in the coronavirus family due to the similarities in structure, replication behavior and the genetic sequencing.[citation needed]
The genus has the following subgenera and species:
Toroviruses (ToV) are single-stranded RNA viruses that have a peplomer-bearing envelope that is often correlated with the enteric infections in cattle and possibly humans. These viruses appear to occur globally, occurrence of ToVs have been reported from countries in various continents like Europe, Americas, New Zealand and South Africa. Torovirus particles typically possess a helical and symmetrical nucleocapsid that is coiled into a hollow cylindrical shape. The diameter is approximately 23 nm with an average length of 104 nm, where every turn cycle is at intervals of 4.5 nm. ToVs are pleomorphic, with size ranging from 100 nm to 150 nm with club-like outgrowths extending from the capsid. A nucleocapsid that is doughnut-shaped with helical symmetry is also discovered in Toroviruses. Among various species of the Toroviruses, only equine torovirus (EToV) can be grown in the cell culture medium due to which EToVs have been most extensively studied. The information from immunofluorescence studies and morphology of the bovine Toroviruses (BToV) intestinal cells has shown similarities among the EToVs and BToVs. Torovirus share some common characteristics with members of the related family Coronaviridae as they are round, pleomorphic, enveloped viruses about 120 to 140 nm in diameter.
Toroviruses have a single piece of single-stranded, positive-sense RNA. The total length is approximately 25-30kb and they possess a complex replication mechanisms that includes the use of subgenomic mRNA, ribosomal frameshifting, and polymerase stuttering. The genomic length of bovine torovirus is approximately 28.5 kb that is mainly comprised by one gene, replicase gene (20.2 kb). This gene contains two open reading frames, ORF1a and ORF1b that encodes proteins pp1a and pp1b. The first genomic sequence of the PToV (porcine torovirus) was done in Shanghai, China in 2014. Genome length of porcine Torovirus was found to be 28301 bp and possess 79% sequence identity with the bovine Torovirus genome.
Cattle, pig, and horse serve as the natural host of Toroviruses and infection is thought to be via the faecal-oral route.
The Torovirus genome encodes for various structural proteins like spikes (S), membrane proteins (M), haemagglutinin‐esterase (HE) and nucleocapsid (N) which provides them the structural characterization necessary for infection and completing their life cycle. The first three proteins coding regions are deleted in the BEV species which enables them to grow in the cell culture, while other species are unable to grow in cell culture. The initial two-thirds of the torovirus genome has two open reading frames, ORF1a and ORF1b. ORFb1 encloses a domain that encodes for the enzymes such as RNA dependent RNA polymerase (RdRp) and the helicase (Hel) that are necessary for transcription and translation of the virus.
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Torovirus
Torovirus is a genus of enveloped, positive-strand RNA viruses in the order Nidovirales and family Tobaniviridae. They primarily infect vertebrates, especially cattle, pigs, and horses. Diseases associated with this genus include gastroenteritis, which commonly presents in mammals. Torovirus is the only genus in the monotypic subfamily Torovirinae.
The discovery of the first torovirus can be traced back to 1970s. Equine torovirus (EToV) was accidentally found in the rectal sample from a horse who was experiencing severe diarrhea. The 'Breda' bovine torovirus was later found in 1979 while investigation in a dairy farm in Breda. They had several calves experiencing severe diarrhea for months. In 1984, torovirus-like particles were detected with electron microscope (EM) technique in the human patients with gastroenteritis.
Until recently, the toroviruses were not assigned any family. The recent molecular analysis of the virus revealed its similarities with Arterivirus and coronaviruses, which led to the inclusion of the Torovirus along with the Arterivirus in the previously monogeneric Coronaviridae. At present, toroviruses are included in the order Nidovirales sub family Torovirinae, family Tobaniviridae. Resemblance, molecular and genetic similarities, virion dimensions, behavioral ties and other characteristic similarities and differences are observed by the researchers for the taxonomic classification of the virus. In the toroviruses, the Berne virus has been extensively studied at the molecular level as compared to its other members. In 1992, the International Committee on Taxonomy of Viruses ICTV got enough data to consider torovirus in the coronavirus family due to the similarities in structure, replication behavior and the genetic sequencing.[citation needed]
The genus has the following subgenera and species:
Toroviruses (ToV) are single-stranded RNA viruses that have a peplomer-bearing envelope that is often correlated with the enteric infections in cattle and possibly humans. These viruses appear to occur globally, occurrence of ToVs have been reported from countries in various continents like Europe, Americas, New Zealand and South Africa. Torovirus particles typically possess a helical and symmetrical nucleocapsid that is coiled into a hollow cylindrical shape. The diameter is approximately 23 nm with an average length of 104 nm, where every turn cycle is at intervals of 4.5 nm. ToVs are pleomorphic, with size ranging from 100 nm to 150 nm with club-like outgrowths extending from the capsid. A nucleocapsid that is doughnut-shaped with helical symmetry is also discovered in Toroviruses. Among various species of the Toroviruses, only equine torovirus (EToV) can be grown in the cell culture medium due to which EToVs have been most extensively studied. The information from immunofluorescence studies and morphology of the bovine Toroviruses (BToV) intestinal cells has shown similarities among the EToVs and BToVs. Torovirus share some common characteristics with members of the related family Coronaviridae as they are round, pleomorphic, enveloped viruses about 120 to 140 nm in diameter.
Toroviruses have a single piece of single-stranded, positive-sense RNA. The total length is approximately 25-30kb and they possess a complex replication mechanisms that includes the use of subgenomic mRNA, ribosomal frameshifting, and polymerase stuttering. The genomic length of bovine torovirus is approximately 28.5 kb that is mainly comprised by one gene, replicase gene (20.2 kb). This gene contains two open reading frames, ORF1a and ORF1b that encodes proteins pp1a and pp1b. The first genomic sequence of the PToV (porcine torovirus) was done in Shanghai, China in 2014. Genome length of porcine Torovirus was found to be 28301 bp and possess 79% sequence identity with the bovine Torovirus genome.
Cattle, pig, and horse serve as the natural host of Toroviruses and infection is thought to be via the faecal-oral route.
The Torovirus genome encodes for various structural proteins like spikes (S), membrane proteins (M), haemagglutinin‐esterase (HE) and nucleocapsid (N) which provides them the structural characterization necessary for infection and completing their life cycle. The first three proteins coding regions are deleted in the BEV species which enables them to grow in the cell culture, while other species are unable to grow in cell culture. The initial two-thirds of the torovirus genome has two open reading frames, ORF1a and ORF1b. ORFb1 encloses a domain that encodes for the enzymes such as RNA dependent RNA polymerase (RdRp) and the helicase (Hel) that are necessary for transcription and translation of the virus.
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