Genus: Sapelovirus


Genus: Sapelovirus

Distinguishing features

Sapeloviruses are most closely related to members of the Enterovirus genus, but possess leader polypeptides of unknown functions. The 2A polypeptide may be a cysteine protease, but it is distinct from that of the enteroviruses. The 2B and 3A proteins are also very different from the enteroviruses. In all three sapelovirus species the IRES is type IV, whereas in all enterovirus species it is type I.

Virion

Morphology

No surface morphology is visible by EM.

Physicochemical and physical properties

Viruses are very stable, resistant to acid pH and elevated temperatures (60°C for 10 min). Buoyant density in CsCl is 1.32-1.34 g cm-3.

Nucleic acid

Length of genome (Krumbholz et al., 2002, Oberste et al., 2003, Tseng and Tsai 2007): c. 7,491-8,226 nt (5'-UTR: up to 741 nt; ORF: 6,969-7,566 nt; 3' UTR: 82-235 nt). The IRES of all three sapelovirus species is type IV. The location of the cre has not been identified.

Genome organization and replication

Genome layout:

VPg+5'UTRIRES-IV[L/1A-1B-1C-1D/2Apro-2B-2C/3A-3B-3C-3D]3'UTR-poly(A)

The deduced polyproteins of the sapaloviruses range from 2,322-2,521 aa. The predicted leader polypeptide of avian sapelovirus (ASV) is the longest known at 451 aa and suspected to be a trypsin-like protease. The leader polypeptide porcine sapelovirus (PSV) and simian sapelovirus (SSV) are much shorter at 84 aa and 88 aa, respectively. The 2A region of ASV is predicted to be mostly deleted with a residual 12 aa remaining. The 2A polypeptides of PSV and SSV are longer at 226 aa and 302 aa, respectively; these are both suspected to be a protease. The L/VP0 cleavage and presence of a potential myristoylation site on VP0 is predicted for ASV (kQ/GqvqS). However, the precise L/VP0 cleavage for PSV or SSV is not clear. The sequences in this region are quite well conserved between the three viruses but it would require unusual cleavages in PSV (qL/GqvhS) and SSV (qC/GqvqS) to generate a myristoylation signal. VP0 is cleaved to VP4 and VP2 as shown by N-terminal sequencing of the VP2 polypeptide for ASV and SSV.

Antigenicity

Sapelovirus A consists of a single antigenically diverse serotype, PSV-1. Avian sapelovirus also consists of a single serotype, ASV-1.

Biology

Sapeloviruses have been isolated from pigs, monkeys and ducks. Sapelovirus-like-specific RNA was also detected in bats (several species), cats, cattle, dogs, pigeons, quails, and sea lions. 

Species demarcation criteria

Members of a species of the genus Sapelovirus have:

  • share greater than 70% aa identity in the polyprotein,
  • share greater than 64% aa identity in P1,
  • share greater than 70% aa identity in 2C + 3CD,
  • a similar genome base composition which varies by no more than 1%,
  • a common genome organization.

The divergence (number of differences per site between sequences) of known Sapelovirus species ranges from 0.39-0.63 for P1 and 0.35-0.51 for 3CD.

Sapelovirus B consists of three genetically-defined simian sapelovirus types, SSV-1 to SSV-3.

Member species

SpeciesVirus name(s)Exemplar isolateExemplar accession numberExemplar RefSeq numberAvailable sequenceOther isolatesOther isolate accession numbersVirus abbreviationIsolate abbreviation
Avian sapelovirusavian sapelovirus TW90AAY563023NC_006553Complete genomeASV
Sapelovirus Aporcine sapelovirus V13AF406813NC_003987Complete genomePSV
Sapelovirus Bsimian sapelovirus SV2-2383AY064708NC_004451Complete genomeSSV

Virus names, the choice of exemplar isolates, and virus abbreviations, are not official ICTV designations.

Derivation of names

Sapelo: sigla from simian, avian and porcine entero-like viruses