Erbovirus | |
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Virus classification | |
Group: | Group IV ((+)ssRNA) |
Order: | Picornavirales |
Family: | Picornaviridae |
Genus: | Erbovirus |
Species | |
Equine rhinitis B virus |
Erbovirus is a viral genus of the Picornaviridae family.[1] Viruses belonging to the Erbovirus genus have been isolated in horses with acute upper febrile respiratory disease.[2] The structure of the erbovirus virion is icosahedral,[1] having a diameter of 27-30 nm.[3]
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The virion essentially is a nucleocapsid that is visible under an electron microscope and is able to infect cultured cells from a broad range of mammals including rabbit kidney (RK13), African green monkey kidney (Vero), equine foetal kidney (EFK), and is able to infect humans.[4]
The RNA genome of the virion is inside the capsid that is composed by twelve capsomers, which are cup-shaped pentamers.
The erbovirus particles are non-enveloped and the molecular mass of the virions is around 8-9 x 106 Daltons.[3] They are resistant to inactivation by non-ionic detergent treatment.[3]
Erbovirus, as a typical picornavirus, has a single-stranded positive-sense RNA genome. A feature of the picornavirus genome is the virus protein that is linked at the 5’ end of the genome, known as "VPg" (Virus-Protein-attached-to-the-Genome).[1] In addition, the 3’ end of the genome has a poly-A tail.[1] The transcription of the erbovirus genome gives rise to a polyprotein which is further more processed and cleaved to give the mature viral proteins, in order from 5' to 3' : L ("Leader"), VP4, VP2, VP3, VP1, 2A, 2B, 2C, 3A (Vpg), 3B, 3Cpro, 3Dpol.[5]
The type (and only) species of the Erbovirus genus is Equine rhinitis B virus which was recently found to have three phylogenetically distinct serotypes, equine rhinitis B virus (ERBV)-1, ERBV-2 and ERBV-3.[6] One such phylogenetic group was found to mostly comprise of "acid stable" virus isolates, surviving pH 3.6 for 1 hour at room temperature.[7]
ERBV's appear to infect most foals and weanlings, eliciting a low serum antibody response in stark contrast to equine rhinitis A virus (ERAV), which is the only species of the genus Aphthovirus that is not a foot-and-mouth disease virus (FMDV), and appears to only infect horses once they begin training for racing (approx. 2 years old). ERAV enters the blood and elicits a very high serum antibody response that seems to then limit the spread of the virus by herd immunity, given that only approximately 40% of horses have detectable ERAV antibody.[8] The low serum antibody response of ERBV appears to allow the continual, seasonal re-infection of horses. Horses are also known to shed ERBV for up to two years, possibly more.