The introduction of a highly virulent PRRSV strain in pig farms is associated with a change in the pattern of influenza A virus infection in nurseries

Abstract

The present study aimed to determine the dynamics of infuenza A virus (IAV) infection in two endemically infectedfarms (F1 and F2), where a longitudinal followup of piglets was performed from birth to 8–12 weeks of age. Dur‑ing the study, a highly virulent isolate of porcine reproductive and respiratory syndrome virus (PRRSV) was intro‑duced on both farms. This allowed us to examine the impact of such introduction on the patterns of infection,disease, and the antibody response of pigs to IAV infection. The introduction of the new PRRSV strain coincidedwith a change in the dynamics of IAV infection on both farms. In F1, the cumulative incidence of IAV increasedfrom 20% before the outbreak to 67.5%, together with the existence of animals that tested positive for IAV (RT‒qPCR)in nasal swabs for two or more consecutive samples. In F2, the cumulative incidence of IAV increased from 50%before the PRRSV outbreak to 70%, and the proportion of prolonged IAV shedders increased sharply. Additionally,some animals were infected with the same IAV twice during the observation period. In contrast to previous reports,our study revealed that prolonged shedding was not related to the titres of maternally derived antibodies at the timeof infection but was signifcantly (p<0.05) related to PRRSV infection status. Notably, both before and after the PRRSVoutbreak, a high proportion of IAVinfected piglets did not seroconvert, which was signifcantly (p<0.05) relatedto the hemagglutination inhibition titres against IAV when infected.