Submitted to: Microbial Pathogenesis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2010
Publication Date: 11/1/2010
Citation: Loving, C.L., Brockmeier, S.L., Vincent, A.L., Palmer, M.V., Sacco, R.E., Nicholson, T.L. 2010. Influenza Virus Coinfection with Bordetella bronchiseptica Enhances Bacterial Colonization and Host Responses Exacerbating Pulmonary Lesions. Microbial Pathogenesis. 49(5):237-245.
Interpretive Summary: Infection with two or more bugs is a common occurrence in respiratory diseases of most animals. However, the manner in which multiple bugs interact is not always straightforward. The effect of coinfection with influenza virus (SIV) and B. bronchiseptica was examined in pigs that were infected with either SIV-only or B. bronchiseptica-only, or both SIV and B. bronchiseptica. Disease was worse in the coinfected pigs as compared to the pigs infected with B. bronchiseptica or SIV alone. SIV disease did not seem to be worse, but influenza virus did make infection the B. bronchiseptica infection worse because more of the bacteria was isolated from the lungs of coinfected pigs. The immune response in coinfected pigs was greater in co-infected pigs also, which may be the cause of the increase in lung disease observed. Thus, there appears to be a synergistic effect between SIV and B. bronchiseptica that causes increased inflammation that may partially explain the increased severity of pneumonia in coinfected pigs. These results indicate that preventing coinfection, through control of Bordetella infection and/or influenza infection, is critical for preventing synergistic disease that is detrimental to pig health and production.
Technical Abstract: Influenza virus (Flu) infection and secondary complications are a leading cause of morbidity and mortality worldwide. The increasing number of annual Flu cases, coupled with the recent Flu pandemic, has amplified concerns about the impact of Flu on human and animal health. Similar to humans, Flu is problematic in pigs, not only as a primary pathogen but as a predisposing agent to secondary bacterial infection. Bordetella species play a role in mixed infections and often colonize the respiratory tract without overt clinical signs. Pigs serve as a valuable animal model for several respiratory pathogens, including Bordetella (Bb) and Flu. To investigate Flu/Bb coinfection pathogenesis, a study was completed in which pigs were inoculated with Flu-only, Bb-only or both agents (Flu/Bb). Results indicate that Flu clearance is not altered by Bb infection, but Flu does enhance Bb colonization. Pulmonary lesions in the Flu/Bb group were more severe when compared to Flu-only or Bb-only groups and Bb did not cause significant lesions unless pigs were coinfected with Flu. The type I interferon response was elevated in co-infected pigs, but increased expression of antiviral genes Mx and PKR did not appear to enhance Flu clearance in co-infected pigs as viral clearance was similar between Flu/Bb and Flu-only groups. IL-1ß and IL-8 were elevated in lungs of co-infected pigs, correlating to the days enhanced lesions were observed. Overall, Flu infection increased Bb colonization and enhanced production of proinflammatory mediators that likely contribute to exacerbated pulmonary lesions.