Torovirus

Toro virus is a genus of currently four types of enveloped viruses with a single-stranded sense RNA ( ssRNA ) as genome. The name of the genus derives from its characteristic feature, one in the electron microscopic representation ring appearing nucleocapsid with helical symmetry. This geometric shape is called a torus, which describes the Basiswulst on a column base in Latin. Toro viruses are pathogens of viral gastroenteritis and diarrhea in humans and some other mammals. You will also be without a disease cause found in some animal species.

Morphology

Due to the circular ( toroidal ) structure of the nucleocapsid of the virus particles in the electron microscope toroviruses have an oval or disc- to kidney- shaped appearance. They are about 120 to 140 nm in size in the largest diameter. As is typical for members of the Coronaviridae, a double wreath of envelope proteins ( spikes ) is incorporated into the viral envelope; This is formed from the non -glycosylated membrane protein M (27 kDa) and a large glycosylated spike protein S ( 200 kDa). The large spikes of the S protein are also as in the subfamily Coronavirinae called Peplomere (Greek peplos: cape, cloak ). In addition, a hemagglutinin -esterase protein HE (65 kDa) is incorporated in the lipid membrane. So far in the toroviruses not found in the small envelope protein E Coronavirinae be proven, which is why a separate subfamily Torovirinae was also formed the basis of sequence analysis

Inside the viral envelope is the annular curved (but not to a complete ring closed ) nucleocapsid. It consists of the nucleocapsid protein N ( 19 kDa), which closes in the helical symmetry of a torus. The nucleocapsid encloses a linear single strand of the genomic ( ) ssRNA.

The viral genome is approximately 25 to 28 kb in size and contains six open reading frames (ORFs, open reading frames ) for the four structural proteins (S, M, HE and N) and two non - structural proteins (RNA polymerase, viral replicase / transcriptase). Two non- coding regions are located at the ends of the RNA (NCR ) at the 5 ' end of a 820 -base-long regulatory sequence and a 3' NCR an approximately 200 bases long section with an additional poly ( A) tail.

Toro viruses replicate in the cytoplasm of intestinal epithelial cells, from which the membrane of the Golgi apparatus to form new virus particles and are discharged without any destruction of the cell. The abundant (but not necessary ), destruction of the infected cell due to the toxicity of the virus proteins or an immunological effect. There is evidence on the basis of sequence analyzes indicate that recombination of viral RNA occurs with simultaneous infection of several Toro virus species within the same cell.

Biological Properties

Some viruses cause gastroenteritis Toro. So the Bredavirus as the causative agent of gastroenteritis with life-threatening diarrhea in calves and possibly pneumonia has been found. No disease has been associated with the equine torovirus (Berne virus), which was isolated in horses. Toro virus virus-like particles were in humans, dogs and cats observed by electron microscopy but not provide evidence of a disease associated, as well as chronic viral infections, have been described without symptoms. In the investigation of children with severe, necrotizing enterocolitis ( NEC), however, the Humane Toro virus was detected in 48% of cases in the chair in a healthy control group at 17 %. All Toro viruses appear to possess, so that cross-reactions of the species are described with each other common antigens on the S- protein. Detection of antibodies also succeeded in sheep and goats.

Note for infection with the Bredavirus is a significant rise in titer of antibody at a present symptoms. Infection with Toro virus is often spread worldwide and the gastroenteritis caused by several species likely the economic importance of the genus Coronavirus not inferior. In Austria, found the Bovine Toro virus in 12 ( 5.2%) of 230 examined newborn calves, 10 with diarrhea .. Comparable data is for South Korea with 2.9 % before. If one examines only diseased calves, one finds, for example, in Japan Bovine toroviruses in 15.2 to 23.7 % of cases.

System

• Genus torovirus

• Species Bovine torovirus

• Subtype Bovine Toro virus ( BToV )
• Subtype Bredavirus ( BRV ) (2 subtypes )

• Equine species torovirus

• Subtype of Berne virus ( BEV)
• Subtype Equine Toro virus ( EToV )

• Human species Toro virus ( HToV )
• Species Porcine Toro virus ( PTOV )