Arteriviridae: A family of viruses, of the order NIDOVIRALES, containing spherical virions. In contrast to CORONAVIRIDAE, no protruding spikes are obvious on the surface.Nidovirales: An order comprising three families of eukaryotic viruses possessing linear, nonsegmented, positive sense RNA genomes. The families are CORONAVIRIDAE; ARTERIVIRIDAE; and RONIVIRIDAE.Arteritis Virus, Equine: The type species of the genus ARTERIVIRUS and the etiologic agent of an important equine respiratory disease causing abortion, pneumonia, or other infections.Arterivirus: A genus of the family ARTERIVIRIDAE, in the order NIDOVIRALES. The type species is ARTERITIS VIRUS, EQUINE.Porcine respiratory and reproductive syndrome virus: A species of ARTERIVIRUS causing reproductive and respiratory disease in pigs. The European strain is called Lelystad virus. Airborne transmission is common.