Oral Swabs for Pigs: A Great Alternative for PRRSV Surveillance

Porcine reproductive and respiratory syndrome virus (PRRSV) remains a major threat to swine health and causes significant economic losses worldwide. Effective surveillance and monitoring are crucial for PRRSV control in breeding herds.

Serum is the gold standard sample for PRRSV RNA detection, but collection is invasive. Oral fluid sampling provides a welfare-friendly alternative, but requires pig interaction with ropes. Oral swabs may offer another easy and non-invasive option, but few studies have evaluated their use for PRRSV surveillance in weaning pigs under field conditions. A study in 2023 aimed to compare PRRSV RT-PCR results from matched oral swab and serum samples collected from weaning pig litters on a breeding farm.

Fifty-one litters from a PRRSV-positive unstable farm were conveniently sampled. All pigs in each litter were restrained and serum obtained via jugular venipuncture. Oral swabs were collected by swabbing the buccal mucosa. All samples were tested for PRRSV RNA by RT-PCR. Within-litter prevalence and mean cycle threshold (Ct) values were calculated. Diagnostic performance was assessed using contingency tables and Cohen’s kappa analysis.

Across all litters, the PRRSV RNA positivity rate was higher in serum (24/51 litters, 83/623 pigs) than oral swabs (15/51 litters, 33/623 pigs). Mean Ct values ranged from 18.9-32.0 for serum and 28.2-36.9 for oral swabs. The probability of PRRSV RNA detection in oral swabs increased as within-litter serum prevalence rose. Serum had 62.5% sensitivity and 100% specificity compared to oral swabs. Cohen’s kappa indicated substantial agreement between sample types.

Key findings demonstrate oral swabs are specific but less sensitive than serum for PRRSV surveillance in weaning pigs. All positive oral swabs came from PRRSV RNA-positive litters, confirming authenticity of positive results. However, some PRRSV-positive serum litters had negative oral swabs, highlighting potential false negatives. The reduced analytical sensitivity of oral swabs must be considered when interpreting negative results.

Overall, oral swabs provide a welfare-friendly sampling alternative for PRRSV surveillance in weaning pigs, but negative results should be cautiously interpreted. Further research could refine sample size recommendations to optimize diagnostic sensitivity.

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Reference

Osemeke OH, VanKley N, LeFevre C, Peterson C, Linhares DCL. Evaluating oral swab samples for PRRSV surveillance in weaning-age pigs under field conditions. Front Vet Sci. 2023 Feb 3;10:1072682. doi: 10.3389/fvets.2023.1072682. PMID: 36876004; PMCID: PMC9976936.