Proventriculitis in broiler chickens and its relationship to infectious bursal disease virus
Pantin-Jackwood, Mary Josephine
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Proventriculitis in broilers causes carcass condemnation because of contamination when swollen proventriculi tear during evisceration. Although the cause of proventriculitis is unknown, infectious bursal disease virus (IBDV) has been implicated. To study the role of IBDV in proventriculitis, proventriculi and bursas were collected from chickens with naturally occurring proventriculitis, and from chickens experimentally infected with seven different IBDV strains. All tissues were examined for IBDV using light microscopy, immunohistochemistry (IHC), real time RT-PCR, and for apoptosis by TUNEL method. We concluded that proventriculitis can occur in the absence of IBDV, and that the IBDV strains tested do not directly produce proventriculitis. Proventriculitis was studied by experimentally reproducing the disease in commercial and specific pathogen free (SPF) broilers. Differences in weight gain, organ weights, and the presence of lesions between these birds and controls were assessed. Bacteria were not identified in histological sections of proventriculi nor were they isolated from affected proventriculi. Attempted virus isolation from affected proventriculi caused stunting in inoculated embryos, and infectious bronchitis virus (IBV) was detected in allantoic fluid. Proventricular homogenates used to induce proventriculitis were positive for IBDV, IBV, adenovirus, and chicken anemia virus (CAV), but proventriculitis could also be produced in chickens in the absence of these viruses. Immunosuppression was induced in broiler chickens using chemicals (cyclophosphamide and cyclosporin) or virus (IBDV) to study the effect of immunosuppression on proventriculitis. Cyclophosphamide and IBDV, both B cell suppressors, did not significantly affect the incidence or characteristics of the proventriculitis induced with a proventricular homogenate from a diseased bird. However, an increase in the size of the proventriculus was observed at 7 days post inoculation. Chickens immunosuppressed with cyclosporin, a T cell suppressor, developed more severe lesions and had a higher incidence of proventriculitis than immunocompetent controls. Although both, B and T cells, are involved in the immune response against proventriculitis, it appears that cell mediated immunity plays a more important role. This was also supported by the lymphocytic infiltrate observed in diseased proventricular glands. CD8+ T lymphocytes were the most common cell type and were widely distributed in the proventriculus, whereas CD4+ T cells and B cells tended to form aggregates in the chronic stages of the disease.