Sampling of adult boars during early infection with porcine reproductive and respiratory syndrome virus for testing by polymerase chain reaction using a new blood collection technique (blood-swab method)

Objectives: To evaluate the effectiveness of a skin puncture technique (blood-swab method) to collect blood for detection of porcine reproductive and respiratory syndrome virus (PRRSV) by polymerase chain reaction (PCR) in experimentally infected boars, and to examine the effect of sampling method (blood swab, serum, semen, or mouth swab) and rectal temperature on the ability to detect PRRSV in boars during the first 6 days after experimental infection. Materials and methods: Twenty-one mature boars were inoculated with PRRSV variant MNB04. Serum samples, blood swabs, mouth swabs, and semen samples were collected from two groups of 10 boars on a rotating basis, one group every 24 hours for 6 days. Rectal temperatures were recorded for all boars every 24 hours. Using the blood-swab method, a vein (usually the auricular vein) was punctured with a needle and blood was collected with a polyester swab. The swab was then put into a tube containing 1 mL of saline solution, which was tested for PRRSV virus by PCR. Results: Sixty of 61 samples were PCR-positive using the blood-swab method compared with 61 of 61 PCR-positive using traditional serum collection methods. Testing of both serum and blood swabs detected PRRS-positive boars earlier and with higher frequency than testing semen samples (27 of 60 positive) or mouth-swab samples (19 of 61 positive). Implications: The blood-swab method is a reliable alternative to traditional venipuncture during the first 6 days after infection with PRRSV, and PCR-testing blood swabs is more sensitive than testing semen or mouth swabs.