Porcine Reproductive and Respiratory Syndrome Isolates and Methods of Use

Abstract

A method of predicting the virulence of a new or uncharacterized PRRS virus strain is provided wherein the strain 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 strain of known virulence, as a measure of the virulence of the new or uncharacterized strain.

1 . A method of predicting the virulence of a PRRS virus strain of unknown virulence, comprising the steps of administering a quantity of said PRRS virus strain into PRRS-free swine, allowing the virus to replicate in said swine for a period of from about 3-15 days, measuring the rate of virus growth and/or the magnitude of viremia during said period, and comparing said rate of growth or viremia magnitude with the rate of growth and/or viremia magnitude of a PRRS virus strain of known virulence as a predictor of virulence of PRRS strain of unknown virulence. 
   
   
       2 . The method of  claim 1 , said period being between from about 3 to 7 days. 
   
   
       3 . The method of  claim 1 , including the step of measuring the magnitude of viremia during said period, and comparing such magnitude with the viremia magnitude of said known PRRS virus strain. 
   
   
       4 . The method of  claim 1 , said quantity of administered virus being similar to the amount an animal would receive by natural exposure. 
   
   
       5 . The method of  claim 1 , said PRRS virus being adminstered by a method selected from the group consisting of oral, intranasal, intramuscular, intra-lymph node, intradermal, intraperitoneal, subcutaneous, and combinations thereof. 
   
   
       6 . The method of  claim 1 , said rate of growth or viremia magnitude being measured in a biological sample from said swine. 
   
   
       7 . The method of  claim 1 , said viremia being measured by Log 10  TCID 50 /ml, reverse transcriptase-polymerase chain reaction, PRRS specific ELISA, PRRS protein-specific ELISA, and combinations thereof. 
   
   
       8 . The method of  claim 1 , further including the step of observing said swine for clinical signs of PRRS infection after administration of said PRRS strain. 
   
   
       9 . The method of  claim 8 , said clinical signs including respiratory signs, behavior, coughing, and combinations thereof. 
   
   
       10 . The method of  claim 1 , further including the step of predicting that the PRRS strain will be of high virulence when its rate of growth or viremia magnitude are similar to that of a strain with high virulence. 
   
   
       11 . The method of  claim 1 , further including the step of predicting that the PRRS strain will be of low virulence when its rate of growth or viremia magnitude are similar to that of a strain of low virulence. 
   
   
       12 . The method of  claim 1 , said administered amount of PRRS virus being up to about 5 ml of inocula having a viral concentration of up to 5.0 Log 10  TCID 50 /ml.