Torovirus is a genus of viruses in the order Nidovirales, in the family Coronaviridae, in the subfamily Torovirinae. They primarily infect vertebrates., especially human, cattle, pig, and horse. There are currently four species in this genus including the type species Equine torovirus. Diseases associated with this genus include: gastroenteritis, which commonly presents in mammals, but rarely in humans.
Torovirus particles share characteristics with other members of the Coronaviridae family; they are round, pleomorphic, enveloped viruses about 120 to 140 nm in diameter. The virus particle has surface spikes proteins that are club-shaped and are evenly dispersed over the surface. A nucleocapsid that is doughnut-shaped with helical symmetry is present.
Viral replication is cytoplasmic. Entry into the host cell is achieved by attachment of the viral S protein (maybe also HE if present) to host receptors, which mediates endocytosis. Replication follows the positive stranded RNA virus replication model. Positive-stranded RNA-virus transcription, using the premature termination model of subgenomic RNA transcription is the method of transcription. Translation takes place by -1 ribosomal frameshifting. Human, cattle, pig, and horse serve as the natural host. Transmission is thought to be via the faecal-oral route.
Toroviruses are class IV viruses, and have a single piece of single-stranded, positive-sense RNA. The total length of this is about 28,000 nucleotides and, like all members of the Coronaviridae, toroviruses have a complex replication mechanism that includes the use of subgenomic mRNA, ribosomal frameshifting, and polymerase stuttering.
In cattle, the disease causes diarrhoea and systemic signs such as pyrexia, lethargy and anorexia. In calves, it may cause neurological signs and lead to death.
Pigs can be infected without showing any signs.
Diagnosis of the viral infection involves electron microscopy, ELISA or haemagglutination inhibition.
Supportive treatment may be given to prevent dehydration and secondary infections.
Control relies on good biosecurity measures including prompt isolation and disinfection of premises.
Porcine torovirus evolved ~1951. Most of the strains appear to fall into two distinct clades.
In 1972, a virus was isolated from a horse in Berne, Switzerland. The virus did not react with antisera against known equine viruses and was shown to have a unique morphology and substructure. In 1982 a similar, unclassified virus was isolated from calves in Breda, Iowa. In 1984 particles resembling these viruses were discovered in the faeces of humans. On the basis of the available information on these viruses, the establishment of a new family of viruses—Toroviridae—was proposed at the 6th International Congress on the Taxonomy of Viruses at Sendai, Japan, but the genus is currently assigned to the subfamily Torovirinae in the family Coronaviridae, order Nidovirales.