Arteriviruses

The family Arteriviridae, which consists of four small, enveloped, positive-strand RNA viruses, was established in 1996. The current members are Equine arteritis virus (EAV), Lactate dehydrogenase-elevating virus (LDV), Porcine reproductive and respiratory syndrome virus (PRRSV), and Simian hemorrhagic fever virus (SHFV). Because arteriviruses share with coronaviruses a similar genome organization, conserved replicase motifs, and a common genome expression strategy, which includes a mechanism of discontinuous RNA synthesis to generate multiple subgenomic RNAs, they have been joined in the order Nidovirales. However, arteriviruses differ from coronaviruses in the smaller size of their genomes, the smaller size and morphology of their virions, and the properties of their structural proteins. The arteriviruses each have distinct narrow host ranges but are widely distributed geographically. Transmission of arteriviruses occurs via the respiratory route or via bodily fluids and in all cases their primary target cells are macrophages. The outcomes of infections with the different arteriviruses range from asymptomatic infections that can be either persistent or acute, to abortion, respiratory disease, arteritis, fatal hemorrhagic fever, and poliomyelitis. Mechanisms that are thought to contribute to persistence include masking of the primary neutralization epitope by glycosylation, the generation of neutralization escape variants, infection of macrophages by immune complexes via Fc receptors, and the presence of an immunodominant decoy epitope near the primary neutralizing epitope.