|Ludemann, Larry -|
Submitted to: Office International Epizootics Manual of Standards for Diagnostic Tests
Publication Type: Book / Chapter
Publication Acceptance Date: March 1, 2008
Publication Date: December 31, 2008
Repository URL: http://oie.int/eng/normes/mmanual/2008/pdf/2.08.07_PRRS.pdf
Citation: Ludemann, L.R., Lager, K.M. 2008. Porcine Reproductive and Respiratory Syndrome. In: OIE Biological Standards Commission, editor. Manual of Diagnostic Tests and Vaccines for Terrestrial Animals 2008: Mammals, Birds and Bees. 6th edition. Paris: Office International Des Epizooties. Volume 2. Chapter 2.8.7. p. 1116-1127. Technical Abstract: Porcine reproductive and respiratory syndrome (PRRS) is the number one disease affecting US swine. It is caused by the PRRS virus (PRRSV) and is recognized as reproductive failure of sows and respiratory problems of piglets and growing pigs. This book chapter is part of the Office of International Epizootics "Manual of Diagnostic Tests and Vaccines for Terrestial Animals," a manual that is designed to standardize veterinary diagnostic methods around the world. It describes the clinical course of PRRS, methodology to diagnose a PRRSV infection (virus isolation techniques, immunohistology, serologic assays, and the polymerase chain reaction), and how commercially available vaccines can be administered and identified. This manual is recognized as the reference standard for diagnostic testing of animals and animal products. The disease is caused by the PRRS virus, a virus currently classified as a member of the order Nidovirales, family Arteriviridae, genus Arterivirus. The primary target cell of the virus is the alveolar macrophage of the pig. Two major antigenic types of the virus exist, the European and the American type. The virus is primarily transmitted via infected pigs but also by faeces, urine, semen, fomites, and aerosol routes. PRRS occurs in most major pig-producing areas throughout the world. The reproductive failure is characterised by infertility, late fetal mummification, abortions, stillbirths, and the birth of weak piglets that often die soon after birth from respiratory disease and secondary infections. Older pigs may demonstrate mild signs of respiratory disease, usually complicated by secondary infections. No other species are known to be naturally infected with PRRSV. Identification of the agent: Virological diagnosis of PRRS virus infection is difficult; the virus can be isolated from tissues such as serum, ascitic fluids, or organ samples, such as lungs, tonsil, lymph nodes and spleen of affected pigs. As porcine alveolar macrophages are the most susceptible culture system for virus of both antigenic types, these cells are recommended for virus isolation. MARC-145 (MA-104 clone) cells are also suitable. There is variability between batches of macrophages in their susceptibility to PRRS virus. Thus, it is necessary to identify a batch with high susceptibility, and maintain this stock under liquid nitrogen until required. The virus is identified and characterised by immunostaining with specific antisera. Additional techniques, such as immunohistochemistry and in situ hybridisation on fixed tissues and reverse-transcription polymerase chain reaction, have been developed for laboratory confirmation of PRRS virus infection. Serological tests: A wide range of serological tests is currently available for the detection of serum antibodies to PRRS virus. The immunoperoxidase monolayer assay uses alveolar macrophages and the indirect immunofluorescence assay uses MARC-145 cells that are usually infected using either the European or the American antigenic type of the virus, respectively. Both assays can however be designed with both cell and PRRS virus types. Commercial or in-house enzyme linked immunosorbent assays (ELISA) are now often used. One commercial ELISA is specific for both the European and American types of the virus. An indirect ELISA, a blocking ELISA and a double ELISA that can distinguish between serological reactions to the European and the American types have been described. Requirements for vaccines and diagnostic biologicals: Vaccines can be of value as an aid in the prevention of reproductive and respiratory forms of PRRS. Modified live vaccines are not suitable for use in pregnant sows and gilts and in boars. Vaccination may result in shedding of vaccinal virus in semen. Modified live virus vaccines can persist in vaccinated animals, and transmission to nonvaccinated animals and subsequent vaccine-virus-induced disease have been reported.