6,502
edits
Changes
Porcine Reproductive and Respiratory Syndrome (view source)
Revision as of 18:34, 27 August 2010
, 18:34, 27 August 2010→Pathogenesis
Line 20:
Line 20:
*Infects alveolar macrophages, followed by '''interstitial pneumonitis'''+
−*Persistent infection of '''[[Monocytes]]''' followed by '''leukopenia and thrombocytopenia'''+*Mostly affects '''piglets'''+*In adults, '''cyanotic''' appearance due to '''vascular lesions'''+*Transplacental spread leads to '''abortion, mummification, or resorption'''+
==Pathogenesis==
==Pathogenesis==
−Transmission of PRRS virus to swine occurs most efficiently
−through direct contact. Blood, saliva, urine, milk
−and semen from infected animals have been shown to
−transmit PRRS virus to susceptible swine (Wills et al.,
+1997). Aerosol transmission may occur but has proven
+difficult to demonstrate even over relatively short distances
+(meters). Transmission by semen, either
+through natural service or artificial insemination is well
+established (Yaeger et al., 1993).
+Following exposure to PRRS virus, primary replication
+occurs in regional or mucosal macrophages (Rossow,
+1998; Rossow et al., 1996a). Typically macrophages of
+the tonsil, nasal and respiratory epithelium are sites of
+primary replication after oronasal exposure. Viremia
+can occur within 12 hours following exposure resulting
+in systemic dissemination of the virus. Lymphatic transport
+of PRRS virus and virus-infected macrophages to
+regional lymph nodes is also thought to occur.
+Secondary replication of PRRS virus occurs in monocyte/
+macrophages in many tissues. While other cell
+types, including fibroblasts, endothelial cells, seminiferous
+epithelium and smooth muscle, have been reported
+to be PRRS virus-positive by in situ hybridization and/or
+immunohistochemistry, only cells of macrophage lineage
+have been unequivocally shown to support PRRS
+virus replication (Sur et al., 1997).
+In most swine, viremia resolves within 4-6 weeks following
+infection. However, PRRS virus can persist in
+lymphoid tissues, such as tonsil, for extended periods of
+time and be transmitted to susceptible swine (Zimmerman
+et al., 1992). PRRS virus has been detected for up
+to 225 days following inoculation, though the proportion
+of positive animals appears to drop off between 80 and
+100 days (Albina et al., 1994; Allende et al., 2000; Wills
+et al., 2003). Persistence occurs in the face of neutralizing
+and other antibodies, and cell mediated immune
+responses, as indicated by gamma-interferon producing
+cells. Studies indicate that a low T cell response
+contributes to prolonged PRRS clearance (Xiao et al.,
+2004). Persistence is of epidemiologic significance
+since persistently infected animals are capable of transmitting
+PRRS virus to susceptible pigs via direct contact
+(Albina et al., 1994). This is likely an important mechanism
+by which PRRS virus is maintained within, and
+transmitted between, swine herds.
==Diagnosis==
==Diagnosis==