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<OL> <LI> Construct an infectious PRRSV clone from a virulent PRRSV field isolate. <LI> Attenuate a virulent PRRSV field isolate (used in Specific Objective 1) through multiple passages in cell culture. <LI> Determine the stability of the attenuated PRRSV strain following infection and passage in pigs. <LI> Determine the nucleotide sequence of the virulent PRRSV field isolate and compare it to the sequence of the attenuated derivative stain and to the nucleotide sequence of viruses reisolated following inoculation of pigs with the attenuated strain. <LI> Develop methodologies to reliably identify pigs persistently infected with PRRSV in typical production conditions.
NON-TECHNICAL SUMMARY: Porcine reproductive and respiratory syndrome (PRRS) is an economically important disease of swine that is characterized by severe and sometimes fatal respiratory and reproductive disease. Current methods of vaccination do not provide uniform control, possibly due to strain variation or inadequate stimulation of the immune system. The objective of this project is to determine which viral genes are responsible for PRRS virulence and persistence. <P>
APPROACH: The role of specific PRRSV viral genes and genomic regions in virulence and persistence will be studied through specific mutations of an infectious clone. An attenuated strain of PRRSV will be obtained by multiple passages in cell culture. Then we will compare the direct sequence of the attenuated strain with the virulent parental strain. This comparison will identify genomic regions that can be studied through mutagenesis experiments with an infectious clone. The stability of the attenuated PRRSV strain will be evaluated following passage in domestic pigs. A comparison will be made of the nucleotide sequences of the attenuated virus to that of the virulent parental strain to determine potential virulent determinants. In addition, methodologies will be developed to reliably identify pigs persistently infected with PRRS in typical production conditions.