Kinetics of influenza A virus nucleoprotein antibody (IgM, IgA, and IgG) in serum and oral fluid specimens from pigs infected under experimental conditions

• Pan influenza A virus (IAV) screening assays rely on the detection of antibody against the highly-conserved IAV nucleoprotein (NP).
• In swine, NP-specific IgM, IgA, and IgG antibodies were detected in both serum and oral fluid over time post inoculation.
• Serum and oral fluid IgG responses were highly correlated in both unvaccinated (r = 0.84) and vaccinated (r = 0.86) groups.
• Oral fluid antibody assays could serve as a cost-effective alternative to serum for surveillance of IAV infections in swine populations.

Indirect influenza A virus (IAV) nucleoprotein (NP) antibody ELISAs were used to compare the kinetics of the NP IgM, IgA, and IgG responses in serum and pen-based oral fluid samples collected from 82 pigs followed for 42 days post inoculation (DPI). Treatment categories included vaccination (0, 1) and inoculation (0, 1) with contemporary H1N1 or H3N2 isolates. Antibody ontogeny was markedly affected by vaccination status, but no significant differences were detected between H1N1 and H3N2 inoculated groups of the same vaccination status (0, 1) in IgM, IgA, or IgG responses. Therefore, these data were combined in subsequent analyses. The correlation between serum and oral fluid responses was evaluated using the pen-based oral fluid sample-to-positive (S/P) ratios versus the mean serum S/P ratios of pigs within the pen. IgM responses in serum and oral fluid were highly correlated in unvaccinated groups (r = 0.810), as were serum and oral fluid IgG responses in both unvaccinated (r = 0.839) and vaccinated (r = 0.856) groups. In contrast, IgM responses were not correlated in vaccinated groups and the correlation between serum and oral fluid IgA was weak (r ∼ 0.3), regardless of vaccination status. In general, vaccinated animals exhibited a suppressed IgM response and accelerated IgG response. The results from this study demonstrated that NP-specific IgM, IgA, and IgG antibody were detectable in serum and oral fluid and their ontogeny was influenced by vaccination status, the time course of the infection, and specimen type.