PATOGENICITÀ DEL VIRUS DELLA BURSITE INFETTIVA GENOTIPO ITA IN POLLI SPF

Infectious bursal disease virus (IBDV) genotype ITA was detected in Italy in IBDlive vaccinated broilers in 2011. The aim of this study was to evaluate in experimental conditions the pathogenicity of ITA genotype in SPF chickens. Birds were inoculated at 35 days of life and observed up to 28 days post-infection (dpi). At specific time points 5 birds were euthanized, subjected to post-mortem examination and sampled. Histopathology of Bursa of Fabricious was performed and tissue distribution was evaluated by qRT-PCR. No clinical signs nor mortality were recorded. At necropsy Bursas of Fabricious showed enlargement and oedema in the acute phase (2nd dpi) of the infection, followed by persistent atrophy, which lasted until the end of the trial. Histology of the Bursa showed lymphocyte depletion, cystic cavities and poor regeneration process. IBDV RNA was persistently detected in bursal tissues until the end of the trial; ITA genotype was also frequently detected in other tissues collected such as thymus, cecal tonsil and spleen. This study showed that ITA genotype, though it has a subclinical course, causes a severe and persistent damage of Bursa tissues. Its circulation in broilers might be a threat for the poultry industry.