Serological evaluation of influenza A virus vaccine antibody responses in replacement gilts on twelve breeding farms in the United States

Authors: CARLSON, J - Iowa State University; Baker, Amy; ZHANG, J - Iowa State University; GAUGER, PHILLIP - Iowa State University

Submitted to: American Association of Swine Veterinarians Annual Meeting
Publication Type: Proceedings
Publication Acceptance Date: 2/1/2018
Publication Date: 3/3/2018
Citation: Carlson, J., Vincent, A.L., Zhang, J., Gauger, P.C. 2018. Serological evaluation of influenza A virus vaccine antibody responses in replacement gilts on twelve breeding farms in the United States. In: Proceedings of the American Association of Swine Veterinarians Annual Meeting, March 3-6, 2018, San Diego, California. https://www.aasv.org/annmtg/.

Interpretive Summary:

Technical Abstract: Introduction Influenza A virus (IAV) is a component of the porcine respiratory disease complex, causing significant economic losses for United States (US) swine producers. As a result, efforts have been made to monitor the presence and distribution of IAV in US swine. However, serological evaluation to detect IAV antibodies and determine immune status in replacement gilts is lacking. This has important implications for vaccination and acclimation protocols for incoming gilts in sow farms. The objective of this study was to assess the presence of IAV antibody in non-vaccinated, new replacement gilts prior to vaccination and post entry into the breeding herd. Materials and methods This study collected 504 serum from 12 swine breeding farms (11 states) representing 4 geographical regions (3 farms per region). Serum was collected from breeding-age gilts prior to initial vaccination (Pre-Vac). A total of 789 serum were collected post vaccination and after gilts were integrated into the breeding herd. Post vaccination samples were collected over three time periods over one year; Post-Vaccination (Post-Vac), Post-Integration 1 (P-Int 1) corresponding to parity 1, and Post-Integration 2 (P-Int 2) corresponding to parity 2. Serum was evaluated with a nucleoprotein (NP) ELISA (IDEXX AI MultiS-Screen AB, Westbrook, ME) and a hemagglutination inhibition (HI) assay using homologous vaccine antigens (commercial or farm-specific) based farm vaccination protocols. The HI assay was also used to evaluate antibody against three H1 phylogenetic clusters (gamma, delta-1b, delta-2) and three H3 antigenic clades (red, green, and human-lineage) representing the predominant IAV currently circulating in swine. Results Collectively, 38.3% (193/504) of the gilts were positive for NP ELISA antibodies, and 50% (6/12) of the farms had at least one NP ELISA positive gilt at Pre-Vac. Influenza HI antibodies to at least one representative antigen were detected in 16.9% (85/504) of the gilts and 41.7% (5/12) farms at Pre-Vac. The farms receiving IAV antibody positive gilts at the Pre-Vac time period included KS, MO, ND, NE, PA, and TX. At Post-Vac, 86.5% (281/325) of the gilts were positive for NP ELISA antibodies excluding only the non-vaccinated ND farm. Additionally, only 71.5% (213/289) of the gilts were HI antibody positive to one or more of their vaccine-specific homologous antigens. The percent of gilts with positive homologous HI antibody titers varied widely across all farms based on vaccine type, individual vaccine antigen, and time period. Replacement gilts lacking Pre-Vac IAV antibody demonstrated more uniform vaccine-induced HI antibody responses such as the NC-2 farm which demonstrated >94.3% of gilts with positive homologous HI antibody titers to all 4 antigens immediately after vaccination (Post-Vac). In contrast, the MO farm demonstrating 87.5% of their gilts with NP ELISA antibody at Pre-Vac had 0.0% of the gilts demonstrating Post-Vac HI antibodies to 3 of 4 homologous vaccine antigens. The TX farm also had 96.0% of gilts NP ELISA positive at Pre-Vac; however, less than 9.1% of gilts demonstrated positive HI antibody titer to all 4 homologous vaccine antigens at Post-Vac. These data suggest new replacement gilts with IAV antibody may induce a non-uniform, inadequate post-vaccination immune response compared to gilts without prior IAV antibody. Conclusions These data demonstrate diversity in the IAV antibody status and their IAV vaccine antibody response in replacement gilts prior to and post vaccination. Approximately 50% of the farms lacked IAV NP ELISA antibody positive gilts suggesting the age, multiplier, and geographical location may influence the IAV antibody status of replacement gilts. More importantly, our data suggests naïve gilts demonstrate a more uniform HI antibody response against vaccine antigens and a higher percentage of gi