The contribution of the immune response to enhanced colibacillosis upon preceding viral respiratory infection in broiler chicken in a dual infection model

Colibacillosis in chickens caused by avian pathogenic Escherichia coli (APEC) is known to be aggravated preceding infections with infectious bronchitis virus (IBV), Newcastle disease (NDV) and metapneumovirus (aMPV). The mechanism behind these virus-induced predispositions for secondary bacterial poorly understood. Here we set out investigate the immunopathogenesis of enhanced respiratory colibacillosis after three viruses. Broilers were inoculated intratracheally APEC six days oculonasal intratracheal inoculation IBV, NDV, aMPV or buffered saline. After euthanasia at 1 8 post infection (dpi) APEC, birds macroscopically examined tissue samples taken from trachea, lungs air sacs. In none groups differences body weight observed during course infection. Macroscopic lesion scoring revealed most severe changes NDV-APEC IBV-APEC Histologically, persistent tracheitis was detected all virus-APEC groups, but not APEC-only lungs, mostly APEC-associated transient pneumonia observed. Severe airsacculitis present Bacterial antigen immunohistochemistry only dpi predominantly NDV-APEC- IBV-APEC-infected lungs. Higher numbers CD4+ CD8+ lymphocytes persisted over time tracheas, as did NBV-APEC- KUL01+ cells, which include monocytes macrophages, TCRγδ+ lung infected higher cells mainly dpi. qPCR analysis trends levels IL-6 IFNγ mRNA also aMPV-APEC spleens, IL-17 more co-infections. No IL-10 expression seen. These results demonstrate a major impact dual viruses compared single on chicken tract suggest that contributes persistence.