Torovirus
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TEM image of the equine torovirus. |
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Toro virus is a genus from three species (all the subgenera Renitovirus ) of enveloped viruses single with one, positive sense - RNA (+ ssRNA) as a genome . The name of the genus is derived from its characteristic feature, a nucleocapsid with helical symmetry that appears ring-shaped in the electron microscope representation . This geometric shape is called a torus , which in Latin describes the base bulge on a column base. Toroviruses cause viral gastroenteritis and diarrhea in humans and some other mammals . They are found in some animal species without causing disease.
morphology
Due to the ring-shaped ( toroidal ) structure of the nucleocapsid, the virus particles of the toroviruses have an oval or disk-shaped to kidney-shaped appearance in the electron microscope . They are around 120 to 140 nm in largest diameter. As is typical for the members of the Coronaviridae , a double ring of envelope proteins ( peplomeres , English spikes ) is embedded in the virus envelope; this is formed from the non- glycosylated membrane protein M (27 kDa ) and the large glycosylated spike protein S (200 kDa). As in the subfamily Coronavirinae, the large spikes of the S protein are also referred to as peplomeres ( Greek peplos , cape, coat ' ). In addition, is hemagglutinin - esterase protein HE (65 kDa) incorporated into the lipid membrane. So far, the small envelope protein E found in the coronavirinae could not be detected in the toroviruses , which is why a separate subfamily Torovirinae was formed on the basis of sequence analyzes .
The nucleocapsid, which is curved in a ring (but not closed into a complete ring), is located inside the virus envelope. It consists of the nucleocapsid protein N (19 kDa), which is arranged in helical symmetry . The nucleocapsid encloses a linear single strand of the genomic (+) ssRNA.
The viral genome is approximately 25 to 28 kb in size and comprises six open reading frames (ORFs, open reading frames ) for the four structural proteins (S, M, U and N) and two non-structural proteins ( RNA polymerase , viral replicase / transcriptase) . At the ends of the RNA there are two non-coding regions (NCR): at the 5 'end an 820 base long regulatory sequence and, as the 3' NCR, an approximately 200 base long section with an additional poly (A) tail .
Toroviruses multiply in the cytoplasm of intestinal epithelial cells , from which new virus particles form on the membrane of the Golgi apparatus and are expelled without destroying the cell. The occurring (but not necessary) destruction of the infected cell is attributed to the toxicity of virus proteins or an immunological effect. There are indications based on sequence analyzes that recombination of viral RNA occurs when several torovirus species are simultaneously infected within the same cell.
Biological properties
Some toroviruses cause gastroenteritis. The Breda virus was found to cause gastroenteritis with life-threatening diarrhea in calves and possibly also pneumonia . No disease could be assigned to the equine torovirus (Bern virus), which was isolated from horses. Torovirus-like virus particles have been observed with an electron microscope in humans, dogs and cats without, however, providing evidence of a disease connection, since chronic viral infections without symptoms have also been described. However, when children with severe necrotizing enterocolitis (NEC) were examined, human torovirus was found in stool in 48% of cases, compared to 17% in a healthy control group. All toroviruses seem to have common antigens on the S protein, so that cross-reactions among species have also been described. Antibodies were also detected in sheep and goats.
An indication of an infection with the Breda virus is a significant increase in the titre of the antibodies if symptoms are present. Torovirus infection is widespread worldwide and the gastroenteritis caused by some species is unlikely to be inferior to the economic importance of the coronavirus genus. In Austria, the bovine torovirus was found in 12 (5.2%) of 230 newborn calves examined, 10 of them with diarrhea. Comparable data are available for South Korea with 2.9%. If only diseased calves are examined, in Japan, for example, bovine toroviruses are found in 15.2 to 23.7% of cases.
Systematics
- Genus Torovirus
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- only subgenus Renitovirus
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- Species Bovine Torovirus (BoTV)
- Subtype bovine torovirus (BToV)
- Subtype Bredavirus (BRV) (2 subtypes)
- Species Equines Torovirus (EqTV)
- Subtype Bern virus (BEV)
- Subtype Equines Torovirus (EToV)
- Species Porcine Torovirus (PoTV)
- Subtype porcine torovirus (PToV)
The species human torovirus was removed from the official list by the International Committee on Taxonomy of Viruses (ICTV) as of November 2018, only a partial genome is available - the same applies to the subtype Bern virus of the equine torovirus .
literature
- EJ Snijder and MC Horzinek: The molecular biology of Toroviruses. In: SG Sidell (Ed.): The Coronaviridae , New York 1995, ISBN 0-306-44972-2
- WJM Spaan et al. : Genus Torovirus . In: CM Fauquet, MA Mayo et al. : Eighth Report of the International Committee on Taxonomy of Viruses . London, San Diego 2005, pp. 956-960 ISBN 0-12-249951-4
- MC Horzinek: Toroviruses (Coronaviridae) . In: A. Granoff, RG Webster (Ed.): Encyclopedia of Virology . San Diego 1999, Volume 3, pp. 1798-1803 ISBN 0-12-227030-4
Web links
Individual evidence
- ↑ ICTV Master Species List 2018b.v2 . MSL # 34, March 2019
- ↑ a b c ICTV: ICTV Taxonomy history: Breda virus , EC 51, Berlin, Germany, July 2019; Email ratification March 2020 (MSL # 35)
- ↑ SL Smits et al. : Phylogenetic and evolutionary relationship among torovirus field variants: evidence for multiple intertypic recombination events . Journal of Virology (2003) 77: pp. 9567-9577
- ↑ Liebler EM, Klüver S, Pohlenz J, Koopmans M: On the importance of the Breda virus as a diarrheal pathogen in calf populations in Lower Saxony . Dtsch Tierärztl Wschr 99: pp. 195-200, 1992
- ↑ A. Lodha et al. : Human torovirus: a new virus associated with neonatal necrotizing enterocolitis . Acta Pediatr. (2005) 94 (8): pp. 1085-1088 PMID 16188853
- ↑ B. Haschek B, D. Klein et al .: Detection of bovine torovirus in neonatal calf diarrhoea in Lower Austria and Styria (Austria) . J. Vet. Med. B. Infect. Dis. Vet. Public. Health (2006) 53 (4): pp. 160-165 PMID 16629982
- ↑ SJ Park et al. : Molecular epidemiology of bovine toroviruses circulating in South Korea . Vet. Microbiol. (2008) 126 (4): pp. 364-371 PMID 17719729
- ↑ R. Kirisawa, A. Takeyama et al. : Detection of bovine torovirus in fecal specimens of calves with diarrhea in Japan . J. Vet. Med. Sci. (2007) 69 (5): pp. 471-476 PMID 17551218
- ↑ ICTV Master Species List 2018a v1 , on: ICTV online, MSL including all taxa updates since the 2017 release. Updates approved during EC 50, Washington, DC, July 2018; Email ratification Fall 2018 (MSL # 33).
- ↑ Virus Metadata Repository , ICTV online: VMR 030118