Porcine reproductive and respiratory syndrome virus (PRRSV) is a member of the genus Arterivirus. The other members are lactate dehydrogenase-elevating virus (LDV) of mice, equine arteritis virus (EAV), and simian hemorrhagic fever virus (SHFV). The arteriviruses as a group exhibit the absolute extremes in mammalian viral pathogenesis. At one end of the spectrum is SHFV, which causes nearly 100% mortality in macaques, with death occurring within 2 weeks of infection. At the other extreme is the infection of mice with LDV, which leads to a life-long asymptomatic infection with levels of viremia approaching 10 million virions per milliliter of blood. These extremes are related to the
different outcomes following the infection of macrophages