Influenza A Virus Surveillance Based on Pre-Weaning Piglet Oral Fluid Samples

Summary Influenza A virus (IAV) surveillance using pre‐weaning oral fluid samples from litters of piglets was evaluated in four ˜12 500 sow and IAV‐vaccinated, breeding herds. Oral fluid samples were collected from 600 litters and serum samples from their dams at weaning. Litter oral fluid samples were tested for IAV by virus isolation, quantitative reverse transcription‐polymerase chain reaction (qRT‐PCR), RT‐PCR subtyping and sequencing. Commercial nucleoprotein (NP) enzyme‐linked immunosorbent assay (ELISA) kits and NP isotype‐specific assays (IgM, IgA and IgG) were used to characterize NP antibody in litter oral fluid and sow serum. All litter oral fluid specimens (n = 600) were negative by virus isolation. Twenty‐five oral fluid samples (25/600 = 4.2%) were qRT‐PCR positive based on screening (Laboratory 1) and confirmatory testing (Laboratory 2). No hemagglutinin (HA) and neuraminidase (NA) gene sequences were obtained, but matrix (M) gene sequences were obtained for all qRT‐PCR‐positive samples submitted for sequencing (n = 18). Genetic analysis revealed that all M genes sequences were identical (GenBank accession no. KF487544) and belonged to the triple reassortant influenza A virus M gene (TRIG M) previously identified in swine. The proportion of IgM‐ and IgA‐positive samples was significantly higher in sow serum and litter oral fluid samples, respectively (P