Erbovirus

Erbovirus is a genus of viruses in the order Picornavirales, in the family Picornaviridae. Horses serve as natural hosts. There is currently only one species in this genus: the type species Erbovirus A. Diseases associated with this genus include: upper respiratory tract disease with viremia and fecal shedding.[1][2][3] Viruses belonging to the genus Erbovirus have been isolated in horses with acute upper febrile respiratory disease.[4] The structure of the Erbovirus virion is icosahedral,[3] having a diameter of 27-30 nm.[5]

Erbovirus
Virus classification
(unranked): Virus
Realm: Riboviria
Kingdom: Orthornavirae
Phylum: Pisuviricota
Class: Pisoniviricetes
Order: Picornavirales
Family: Picornaviridae
Genus: Erbovirus
Type species
Erbovirus A
Species

Erbovirus A

Taxonomy

Group: ssRNA(+)

[2]

Physical characteristics

Viruses in Erbovirus are non-enveloped, with icosahedral, spherical, and round geometries, and T=pseudo3 symmetry. The diameter is around 30 nm. Genomes are linear and non-segmented, around 8.8kb in length.[1]

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.[6]

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.[5] They are resistant to inactivation by non-ionic detergent treatment.[5]

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).[3] In addition, the 3’ end of the genome has a poly-A tail.[3] 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.[7]

The type (and only) species of the genus Erbovirus 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.[8] One such phylogenetic group was found to comprise mostly "acid stable" virus isolates, surviving pH 3.6 for 1 hour at room temperature.[9]

GenusStructureSymmetryCapsidGenomic arrangementGenomic segmentation
ErbovirusIcosahedralPseudo T=3Non-envelopedLinearMonopartite

Life cycle

Viral replication is cytoplasmic. Entry into the host cell is achieved by attachment of the virus to host receptors, which mediates endocytosis. Replication follows the positive stranded RNA virus replication model. Positive stranded RNA virus transcription is the method of transcription. Translation takes place by ribosomal skipping. The virus exits the host cell by lysis, and viroporins. Horses serve as the natural host.[1]

GenusHost detailsTissue tropismEntry detailsRelease detailsReplication siteAssembly siteTransmission
ErbovirusHorseNoneCell receptor endocytosisLysisCytoplasmCytoplasmContact

Epidemiology

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.[10] 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.

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References
  1. "Viral Zone". ExPASy. Retrieved 15 June 2015.
  2. ICTV. "Virus Taxonomy: 2014 Release". Retrieved 15 June 2015.
  3. "Notes on Genus: Erbovirus". dpvweb. Retrieved 16 March 2007.
  4. Dynon K, Black W, Ficorilli N, Hartley C, Studdert M (2007). "Detection of viruses in nasal swab samples from horses with acute, febrile, respiratory disease using virus isolation, polymerase chain reaction and serology". Aust Vet J. 85 (1–2): 46–50. doi:10.1111/j.1751-0813.2006.00096.x. PMID 17300454.
  5. "Erbovirus". ICTVdb. Retrieved 16 March 2007.
  6. Kriegshäuser G, Deutz A, Kuechler E, Skern T, Lussy H, Nowotny N (2005). "Prevalence of neutralizing antibodies to Equine rhinitis A and B virus in horses and man". Vet Microbiol. 106 (3–4): 293–6. doi:10.1016/j.vetmic.2004.12.029. PMID 15778036.
  7. Wutz G, Auer H, Nowotny N, Grosse B, Skern T, Kuechler E (1996). "Equine rhinovirus serotypes 1 and 2: relationship to each other and to aphthoviruses and cardioviruses". J Gen Virol. 77 ( Pt 8) (8): 1719–30. doi:10.1099/0022-1317-77-8-1719. PMID 8760418.
  8. Black W, Studdert M (2006). "Formerly unclassified, acid-stable equine picornaviruses are a third equine rhinitis B virus serotype in the genus Erbovirus". J Gen Virol. 87 (Pt 10): 3023–7. doi:10.1099/vir.0.81937-0. PMID 16963761.
  9. Black W, Hartley C, Ficorilli N, Studdert M (2005). "Sequence variation divides Equine rhinitis B virus into three distinct phylogenetic groups that correlate with serotype and acid stability". J Gen Virol. 86 (Pt 8): 2323–32. doi:10.1099/vir.0.80778-0. PMID 16033980.
  10. Black W, Wilcox R, Stevenson R, Hartley C, Ficorilli N, Gilkerson J, Studdert M (2007). "Prevalence of serum neutralising antibody to equine rhinitis A virus (ERAV), equine rhinitis B virus 1 (ERBV1) and ERBV2". Vet Microbiol. 119 (1): 65–71. doi:10.1016/j.vetmic.2006.08.031. PMID 17046179.
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