The applicability of pig oral fluid in laboratory diagnostics of porcine reproductive and respiratory syndrome and its effectiveness in controlled exposure of gilts.

Background: Porcine reproductive and respiratory syndrome (PRRS) remain a major challenge for swine health and production, and effective control depends on successful acclimation of replacement gilts. Natural exposure is commonly used but offers limited control over infection timing and immune response. This study evaluated the use of PRRS virus (PRRSV)-contaminated oral fluid (OF) ropes as an additional or sole acclimation tool and assessed the usefulness of serum and OF for monitoring PRRSV infection. Methods: Ninety-six (96) PRRSV-naïve replacement gilts were allocated to six groups (16 gilts each) and exposed to PRRSV by natural contact with infected pigs, natural exposure combined with OF-contaminated ropes, or OF-contaminated ropes alone. PRRSV RNA and anti-PRRSV antibodies were monitored weekly for 9 weeks using RT-PCR and ELISA in individual serum samples and group OF samples. Results: PRRSV infection and seroconversion occurred in all gilts exposed through natural contact, whereas exposure to OF-contaminated ropes alone did not result in consistent infection or acclimation. Gilts receiving additional exposure via contaminated ropes showed significantly earlier detection of viremia and more gilts were deemed non-viremic sooner compared with gilts exposed only by natural contact. Significant differences in antibody responses between treatment groups were observed at several time points. Detection of PRRSV RNA and antibodies in OF generally reflected serum results, although variability in antibody detection in OF was noted. Conclusion: Supplemental exposure using PRRSV-contaminated OF accelerates infection and immune response during gilt acclimation when combined with natural exposure but is insufficient as a standalone method. Oral fluid sampling represents a practical tool for monitoring PRRSV acclimation under field conditions.