Submitted to: American Association of Veterinary Laboratory Diagnosticians
Publication Type: Proceedings
Publication Acceptance Date: 10/18/1996
Publication Date: N/A
Technical Abstract: A new test was recently developed in our laboratory which can differentiate strains of PRRSV, thus adding a new dimension to our pathogenesis studies and field investigations. We can now identify PRRSV strains in pigs; however, we do not know the sensitivity and specificity of this test for identifying mixed PRRSV infections. Therefore, we undertook the following study to answer the question, Can one differentiate a dual PRRSV infection in pigs? Preliminary in vitro experiments were conducted to test our ability to identify a mixed virus infection. Solutions containing field (NADC-9) and vaccine (RespPRRS) virus in varying concentrations were inoculated onto monolayers of the permissive cell line, MARC-145. When CPE was observed, the total RNA was harvested from the infected cells and subjected to a PRRSV specific RT-PCR procedure to amplify a 716 bp region of viral genome. PCR product was digested with restriction enzyme Mlu I to differentiate the PRRSV strains by agarose gel electrophoresis. Results of this trial suggested we could detect a dual infection in serum if the two strains were present in roughly the same proportion or if more NADC-9 PRRSV was present than RespPRRS. However, if RespPRRS PRRSV was the predominant virus in the test sample, then we would be unable to identify the NADC-9 strain due to in vitro overgrowth and amplification of the cell culture adapted vaccine virus. Twenty-five pigs were allotted to 5 experimental groups and exposed to either sham inoculum, RespPRRS, NADC-9 or double exposures to both viruses. Serum was harvested from the pigs and tested for both strains of virus. The conclusion of the in vivo experiments will be reported at the annual meeting.