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The objective of this study was to evaluate the correlation between serum PRRSv PCR positives and oral fluids PRRSv PCR positives, to evaluate the detection dynamics between serum and oral fluids PRRSv PCR positives, and to determine the effects of pooling samples.
Serum and oral fluid samples were collected from six month old gilts in isolation barns from five different sites. Each pen of gilts (average of 24 pens/barn) was sampled at entry into isolation (Day 0) and again between 20-27 days after entry. In each pen, one oral fluid collection rope was suspended for approximately twenty minutes before removal and harvest of oral fluids. After oral fluids collection, serum samples were obtained from three randomly chosen gilts per pen. Following sample collection on Day 0, the gilts were given a modified live PRRSv vaccine. Serum samples were tested utilizing PRRSv ELISA and PCR on individual samples as well as PRRSv PCR in pools of 3 by pen. Oral fluids were tested by PRRSv PCR individually by pen and in pools of two, three, and six pens (2:1, 3:1, and 6:1).
Results and discussion
Pigs sampled at Sites 1, 3, 4 and 5 were 100% negative by PRRSv PCR for both individual and pooled serum and oral fluids on Day 0. Site 2 had 6% PRRSv PCR positive oral fluid samples when tested individually on Day 0, and had 6% positive when pooled at 2:1, 10% positive when pooled 3:1, and 0% positive when pooled 6:1. The individual and pooled serum samples for Site 2 on Day 0 were 100% negative. On average, the percent positive individual serum samples tested by PRRSv PCR after 20-27 days was 54% for all sites. Similarly, the percent PRRSv positive for serum pooled by pen number was 73%. For individual pen testing of oral fluids at the second sampling interval, the average percent PRRSv PCR positive was 43% across all sites. In contrast, the percent PRRSv PCR positive for oral fluids pooled 2:1, 3:1 and 6:1 were 42%, 41% and 50%, respectively. Sera tested by PRRSv ELISA averaged 0% PRRSv positive on Day 0. Day 20-27 ELISA results were 94% and 97% average positives for individual and pooled samples respectively.
These results suggest that oral fluid sampling for PRRSv could be a practical substitute for blood sampling and that the oral fluid sample pooling ratios tested appear to provide adequate sensitivity when compared to sera. This should help swine practitioners with the decision to use oral fluid testing to survey for PRRSv or to continue with the current method of blood sampling. If the practitioner chooses to use oral fluids, the present results provide guidelines to determine whether oral fluid samples should be tested individually or pooled at 2:1, 3:1, or 6:1.
W. Weeks, R. Jones, G. Cline, D. Polson.A comparison of PRRS virus PCR testing methods: Serum PCR versus oral fluid PCR. 2010 AASV Annual Meeting: Implementing Knowledge, 352.
