Establishing sensitivity and specificity of using rope samples (saliva) to test for PRRS virus antibodies

Project 17-016 - Lead Researcher: Dr. Tim Blackwell

Project 17-016
Researcher: Dr. Tim Blackwell, OMAFRA
Student: Emily Croft, University of Guelph
Project Start: May 2018  Project Completion: February 2019

Establishing the sensitivity and specificity of using rope samples (saliva) to test for antibodies to the PRRS virus 

FINAL REPORT

Porcine Reproductive and Respiratory Syndrome (PRRS) causes disease and economic losses on swine farms. Producers strive to eradicate the virus if geographically feasible or “stabilize” the sow herd through vaccination or intentional field virus exposure. A cornerstone of any PRRS management procedure includes monitoring the PRRS status of sows and growing pigs. The conventional approach is to collect and test blood samples for PRRS by PCR (virus) or by ELISA (antibodies). Recently oral fluid testing has gained popularity for disease monitoring. It is simpler and often less expensive than blood sampling. PRRS virus may be in the blood or oral fluid for days or months following infection while PRRS antibodies persist for upwards of a year following infection. Therefore testing for PRRS antibodies is a key component of many monitoring programs. The Animal Health Lab (AHL), University of Guelph, suspects that false positive reactions are occurring when the PRRS ELISA antibody test is done on oral fluids. The AHL however lacks data to support this hypothesis and does not know if or how often false positive reactions occur. 

Thirty-two facilities with growing swine were selected for this trial.  The PRRS status of the barn was initially based on the producers’ self-assessment which may or may not have included recent laboratory testing.  Six cotton ropes were hung randomly throughout each of the 32 facilities.  After 30 minutes oral fluids were collected from the ropes and immediately sent to the Animal Health Laboratory at the University of Guelph for testing with the IDEXX PRRS Oral Fluids ELISA Ab Test.  Where disagreements occurred between the owners’ assessment of the PRRS status of the barn and the results of oral fluid testing, blood samples were used to resolve the discrepancy. 

All 32 herds were correctly categorized as a result of this testing.  On three farms initially classified by the owner as PRRS naïve, oral fluid samples tested strongly positive.  Subsequent blood testing in these herds indicated that the herds were clearly PRRS antibody positive indicating that the oral fluid samples had correctly classified the herd PRRS antibody status.

Conclusions: The use of oral fluids correctly identified the PRRS antibody status of all 32 farms in this study.  Oral fluids are a simple, easy, and convenient method to measure the presence or absence of PRRS antibodies in growing pigs.  The rare occurrence of false positive and false negative reactions in this study were resolved without the need to transfer samples to Iowa State University for confirmatory testing.


Additional resources:
2018 Shakespeare Swine Seminar proceedings page 42