Genus Arterivirus

Type Species	Equine arteritis virus	(EAV)

Distinguishing Features

The members of the genus Arterivirus form a distinct phylogenic group. The genome encodes two large 5 ORFs, ORFs 1a and 1b, that are expressed from the genomic RNA. ORF1b is only expressed after a -1 frameshift has occurred. The 3 ORFs encode structural proteins and are expressed from a set of 3- and 5- co-terminal subgenomic mRNAs. Virions contain 1 major and 1 to 3 minor envelope glycoproteins. The arterivirus nucleocapsid is isometric. The virion surface projections are relatively small and indistinct and none of the virion glycoproteins contain a coiled-coil structure. While both the arterivirus M and N polypeptides are smaller than those of the members of the family Coronaviridae, the difference in the sizes of the N proteins is considerable.

List of Species Demarcation Criteria in the Genus

The genus Arterivirus is comprised of four species, EAV, LDV, PRRSV, and SHFV. Each species is a phylogenetic branch within the genus (Fig. 3). Each species is represented by a cluster of strains. LDV, PRRSV, and SHFV are more closely related to each other than they are to EAV. The arterivirus genome ranges in size from 12.7  kb (EAV) to 15.7  kb (SHFV). There are two ‘subspecies’ of PRRSV, an American and a European. The amino acid identity between the ORF1b polyproteins of American (VR2332) and European (LV) PRRSV is 75.7%, while the identity between the ORF1b proteins of PRRSV (LV) and LDV (LDV-P) is 55.2%. The amino acid identities between the nucleocapsid proteins of the prototype, EAV, and the other three arteriviruses range from 22 to 33.3%. The four virus species are antigenically distinct. Each species has a restricted host range but infects different hosts. The variability in the length of the N-terminal region of ORF1a among arteriviruses suggests that this region may contain species-specific functions.

List of Species in the Genus

Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names, genome sequence accession numbers [ ], and assigned abbreviations ( ) are:

Species in the Genus

Equine arteritis virus	[X53459]	(EAV)
Lactate dehydrogenase-elevating virus	[L13298, U15146]	(LDV)
Porcine respiratory and reproductive syndrome virus	[U87392, M96262]	(PRRSV)
Simian hemorrhagic fever virus	[U63121]	(SHFV)

Tentative Species in the Genus

None reported.

Phylogenic Relationships within the Family

See Fig. 3.

Similarity with Other Taxa

Members of the family Arteriviridae have a genome organization and replication strategy similar to those of the members of the family Coronaviridae, but arterivirus genomes and virions are about half the size of those of the coronaviruses. Arteriviruses and other nidoviruses have SDD instead of the canonical GDD in their polymerases and contain a nidovirus-specific domain at the C-terminus of the ORF1b protein. There are also some similarities between the genome organization of the arteriviruses and that of the members of the plant virus family Potyviridae.

Derivation of Names

Arteri: from equine arteritis, the disease caused by the reference virus.