Toroviruses (Coronaviridae)

Toroviruses are single-stranded RNA peplomer-bearing enveloped viruses producing enteric disease in animals and humans. They have a unique extracellular C-shape or open torus morphology. There are four species in the genus Torovirus (family Coronaviridae, order Nidovirales): Equine torovirus (EToV), Bovine torovirus (BToV), Human torovirus (HToV), and Porcine torovirus (PToV), which have been reported worldwide. Their genome contains six ORFs, which are transcribed as a 3’-coterminal nested set of four mRNAs. ORF1a and 1b encode the replicase, and ORFs 2–5 encode the spike (S), membrane (M), hemagglutinin-esterase (HE), and nucleocapsid (N) proteins, respectively. Only EToVs and BToV Aichi/2004 propagate in cell culture.