Pre-infection of pigs with Mycoplasma hyopneumoniae induces oxidative stress that influences outcomes of a subsequent infection with a swine influenza virus of H1N1 subtype.

The severity of swine influenza is highly variable and can be exacerbated by many factors, such as a pre-infection of pigs with Mycoplasma hyopneumoniae (Mhp). The aim of this study was to investigate the oxidative stress induced by Mhp and the impact of this stress on the evolution of an infection with the European avian-like swine H1N1 influenza virus. Two experimental trials (E1 and E2), which differed only by the feed delivered to the animals, were conducted on SPF pigs. In each trial, one group of nine 6-week-old pigs was inoculated intra-tracheally with Mhp and H1N1 at 21 days intervals and a mock-infected group (8 pigs) was included. Clinical signs were observed, blood samples were collected throughout the study and pathogens were detected in nasal swabs and lung tissues. Results indicated that Mhp infection induced an oxidative stress in E1 and E2, but its level was more important in E2 than in E1 three weeks post-Mhp inoculation, before H1N1 infection. In both trials, a strong inflammatory response and a response to the oxidative stress previously induced by Mhp appeared after H1N1 infection. However, the severity of influenza disease was significantly more marked in E2 as compared to E1, as revealed by prolonged hyperthermia, stronger reduction in mean daily weight gain and earlier viral shedding. These results suggested that severity of flu syndrome and reduction in animal performance may vary depending on the level of oxidative stress at the moment of the influenza infection, and that host responses could be influenced by the feed.