Pregnancy outcome and clinical status of gilts following experimental infection by H1N2, H3N2 and H1N1pdm09 influenza A viruses during the last month of gestation

Abstract

The present study was planned to study the effect of various subtypes of swine influenza virus (SIV) circulating among pigs (H1N2, H3N2 and emerging pandemic strain of H1N1 influenza A virus (H1N1pdm09) on the course of pregnancy in naïve gilts experimentally infected during the last month of pregnancy. In addition, the clinical course of infection, distribution of viruses in various tissues (blood, placenta, fetal lung), and selected immunological, reproductive and productive parameters were also investigated. All SIV-inoculated gilts became infected. No abortions, stillbirths, intrauterine deaths or mummified fetuses were observed. No clinical signs of influenza virus infection or other disorders were observed in piglets born from infected and control gilts. There was a significant decrease in the number and frequency of lymphocytes in gilts inoculated with all influenza viruses. In general, the concentrations of IL-6, IL-10 and TNF-α were significantly higher in SIV-inoculated gilts as than in control animals, while IL-4 and IFN-γ were not detected in plasma at any time post-inoculation in SIV- or mock-inoculated gilts. No evidence for transplacental transmission of SIV was found. Viremia was also not observed in any of the infected females. On the basis of recent results, we hypothesize that pregnancy failure observed during SIV infection under field conditions is probably related to high fever and pro-inflammatory cytokines rather than a direct effect of the virus on the placenta, embryo or fetus.