The use of oral fluids as a tool for monitoring porcine circovirus type 2 viremia

Porcine circovirus type 2 (PCV2) is a ubiquitous pathogen that causes significant economic losses in growing pigs. While effective commercial vaccines are available, the recent emergence of a possibly more virulent variant, PCV2d, poses challenges for understanding the potential impact of PCV2d on subclinical disease due to viremia and overall environmental levels and shedding. Accordingly, a monitoring tool for evaluating herd-level infection status is needed. Oral fluids are routinely used as a non-invasive sample for monitoring other population diseases such as PRRS and IAV-S. The objective of our study was to determine if testing oral fluids by PCR could be used to monitor the PCV2 infection status of growing pigs rather than the more common method of testing serum for viremia by PCR.

Samples were collected in one barn on each of 32 finishing farms, representing 28 sow flows. All pigs received commercial PCV2 vaccine according to the production system’s standard protocols. One week prior to the first marketing event, 6 oral fluid samples (OFL) were collected per barn and from the same pens, 5 pigs that were observed to chew the rope were bled to obtain serum. Samples were tested by PCR at the Iowa State University Veterinary Diagnostic Laboratory using standard methods. Serum samples (SER) were pooled by pen. Statistical analyses included Chi square and linear regression.

A total of 960 market hogs were sampled generating 192 OF and SER. Overall, 39.1% of SER and 77.6% of OFL were positive. Comparing the two sample types on a pen basis, 21.9% were negative on both, 39.1% were SER- and OFL+, 0.50% were SER+ and OFL- and 38.5% were positive on both (p< 0.05). Within pen correlation of CT values was highly significant. On a barn basis, 37.5% were SER all negative, 15.6% SER all positive, 6.3% OFL all negative and 62.5% OFL all positive. The relationship between the two tests was not significant on a pos/neg basis but was highly correlated when comparing the average CTs.

Positive PCR results on oral fluids for PCV2 have been regarded as representing the level of environmental virus with little correlation with the level of infection/viremia in the pigs. This study proposes that oral fluids represent more than environmental viral load and can be used to estimate the levels of PCV2 viremia and viral shedding within a population of growing pigs. This monitoring technique can be a valuable tool for veterinarians and producers because it is easy to perform and is non-invasive to pigs compared to other methods such as collecting blood or tissue.

Disclosure of Interest: None Declare.