PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME ISOLATES AND METHODS OF USE

摘要

A method of predicting the virulence of a new or uncharacterized PRRS virus isolate is provided wherein the isolate is injected into swine and allowed to replicate for a period of from about 3-15 days. During this period, the rate of virus growth and/or the magnitude of viremia is determined, and this data is compared with a corresponding growth rate and/or viremia magnitude of a PRRS virus isolate of known virulence, as a measure of the virulence of the new or uncharacterized isolate. Additionally, a method of selecting an isolate for inclusion in an immunogenic composition based on the predicted virulence is also provided, together with compositions incorporating attenuated forms of viruses predicted to be virulent.