PRRS Fact Sheet for Animal Science

North Carolina State University Animal Science Fact Sheet ANS01-817S. Since 1987 when the first epidemics of Porcine Reproductive and Respiratory Syndrome (PRRS) were recognized in the United States it has spread to most countries in the world where pigs are raised. In doing so, it has cost the industry an enormous amount of money and frustrated farmers as they try to exclude the disease from their herds or control its sometimes-devastating effects on production. At this time, only Sweden and Australia are presumed negative. In the early days, PRRS was known by a variety of names usually describing the associated clinical signs. In the USA it was initially called iamystery swine diseasely reflecting the frustration researchers experienced as they attempted to identify the cause. In Mexico it was called iablue ear diseaseld and in other countries ioporcine epidemic abortion and respiratory syndromelr and inswine infertility and abortion syndromelt. In 1991 researchers at the Central Veterinary Research Institute in Lelystad, The Netherlands, were able to reproduce the reproductive signs of the disease with a virus. The strain isolated in Lelystad (LV), while similar to the US strain (VR-2332), is sufficiently different genetically and antigenically to be a distinct strain. Outbreaks in Europe are usually caused by strains like the LV and outbreaks in the Americas (and countries purchasing breeding stock from there) are usually caused by variant strains more similar to VR-2332. Subsequently, we have come to realize that many different strains of the virus exist with differing virulence, tissue trophism, and ability to replicate. PRRS is a member of the family of viruses called Arterividae and, in common with other members of this group (lactate dehydrogenase-elevating virus, equine arteritis virus, and simian haemorrhagic fever virus), they cause a variety of clinical signs ranging in severity from subclinical to fatal. In addition, they persist in the host, replicate in white blood cells (macrophages) and mutate readily. These attributes contribute to many of the difficulties we have in trying to cope with PRRS.