Biomarkers associated with vaccine-associated enhanced respiratory disease following influenza A infection in swine

Authors: Wymore Brand, Meghan; SOUZA, CARINE - Iowa State University; GAUGER, PHIL - Iowa State University; Arruda, Bailey; Baker, Amy

Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2024
Publication Date: 5/23/2024
Citation: Wymore Brand, M.J., Souza, C.K., Gauger, P., Arruda, B.L., Baker, A.L. 2024. Biomarkers associated with vaccine-associated enhanced respiratory disease following influenza A infection in swine. Veterinary Immunology and Immunopathology. https://doi.org/10.1016/j.vetimm.2024.110787.
DOI: https://doi.org/10.1016/j.vetimm.2024.110787

Interpretive Summary: Influenza A is a significant concern in the swine industry, and there is extensive use of adjuvanted whole inactivated virus (WIV) influenza vaccines. These vaccines are highly effective against similar viruses, but provide limited protection against antigenically different viruses and in swine research studies have been demonstrated to lead to vaccine-associated enhanced respiratory disease (VAERD). VAERD results in severe respiratory disease and has repeatedly been demonstrated in research studies. However, the significance of VAERD in swine production systems is unknown, in part due to lack of established clinical parameters or biomarkers for diagnosis. This study evaluated various measurements in pig blood and bronchoalveolar lavage fluid to find those differentiating VAERD from uncomplicated influenza A infection. We demonstrated swine influenza A VAERD was associated with an increase in white blood cells and neutrophils and the acute phase proteins c-reactive protein and haptoglobin, and the cytokine IL-8 in bronchoalveolar lavage fluid compared to non-vaccinated infected pigs. Additionally, we demonstrated VAERD is associated with an increased modified histone that is associated with neutrophil extracellular trap formation and may be relevant in the pathogenesis of VAERD. These data, along with knowledge of whole inactivated virus vaccine use and infecting influenza A strain, provide an initial clinical diagnostic assessment of potential biomarkers for field diagnosis of VAERD. These biomarkers may be useful if a swine veterinarian is suspicious for VAERD, or in research studies for VAERD diagnosis without requiring animal sacrifice.

Technical Abstract: Influenza A virus (IAV) is a major pathogen in the swine industry. Whole-inactivated virus (WIV) vaccines in swine are highly effective against homologous viruses but provide limited protection to antigenically divergent viruses and may induce vaccine-associated enhanced respiratory disease (VAERD). Although VAERD is reproducible in laboratory studies, clinical diagnosis is challenging, as it would require both knowledge of prior vaccine history and evidence of severe disease by assessment of pathologic lesions at necropsy following infection with a heterologous virus. The objective of this study was to identify potential biomarkers for VAERD for antemortem clinical diagnosis. Naïve pigs were split into two groups, and one group was vaccinated with IAV WIV vaccine. All pigs were then challenged with a heterologous virus to induce VAERD in the vaccinated group and necropsied at 5 days post infection (dpi). Blood was collected on 0, 1, 3, and 5 dpi, and assessed by hematology, plasma chemistry, acute phase proteins, and citrullinated H3 histone (CitH3) assays. Additionally, cytokine and CitH3 levels were assessed in bronchoalveolar lavage fluid (BALF) collected at necropsy. Compared to nonvaccinated challenged pigs, blood collected from vaccinated and challenged (V/C) pigs with VAERD had elevated white blood cells and neutrophils, elevated c-reactive protein and haptoglobin acute phase proteins, and elevated CitH3. In BALF, the proinflammatory cytokine IL-8 and CitH3 were elevated in V/C pigs. In conclusion, a profile of elevated white blood cells and neutrophils, elevated c-reactive protein and haptoglobin, and elevated CitH3 may be relevant for a clinical antemortem IAV VAERD diagnosis.