Background: The object of this study was to describe and contrast the kinetics of the humoral response in serum and oral fluid specimens during acute porcine reproductive and respiratory syndrome virus (PRRSV) infection. The study involved three trials of 24 boars each. Boars were intramuscularly inoculated with a commercial modified live virus (MLV) vaccine (Trial 1), a Type 1 PRRSV field isolated (Trial 2), or a Type 2 PRRSV field isolate (Trial 3). Oral fluid samples were collected from individual boars on day post inoculation (DPI) -7 and 0 to 21. Serum samples were collected from all boars on DPI -7, 0, 7, 14, 21 and from 4 randomly selected boars on DPI 3, 5, 10, and 17. Thereafter, serum and oral fluid were assayed for PRRSV antibody using antibody isotype-specific ELISAs (IgM, IgA, IgG) adapted to serum or oral fluid.
Results: Statistically significant differences in viral replication and antibody responses were observed among the three trials in both serum and oral fluid specimens. PRRSV serum IgM, IgA, and IgG were first detected in samples collected on DPI 7, 10, and 10, respectively. Oral fluid IgM, IgA, and IgG were detected in samples collected between DPI 3 to 10, 7 to 10, and 8 to 14, respectively.
Conclusions: This study enhanced our knowledge of the PRRSV humoral immune response and provided a broader foundation for the development and application of oral fluid antibody-based diagnostics.