Pathogenicity of a new italian genotype of Infectious Brusal Diases Virus in SPF chickens

Infectious Bursal Disease (IBD) is a highly contagious immunosuppressive disease of chickens caused by a Birnaviridae (IBDV). The ITA genotype was first detected in 2011 in Italy in IBD-live vaccinated chickens. Full genome characterization confirmed ITA to be a genetically dis-tinctive IBDV. The aim of the study was to determine the pathogenicity of the ITA genotype in SPF chickens. Birds were housed in poultry isolators and inoculated at 35 days of life with ITA or STC IBDV strains. A control group was housed in analogous conditions and inoculated with sterile water. All groups were daily observed for clinical signs up to 28 days post-inoculation (dpi). At 0, 7, 14, 21 and 28 dpi birds were bled for IBDV antibody detection by an ELISA Kit. At 2, 4, 7, 14, 21 e 28 dpi 5 birds from each of the inoculated groups, and 3 from the control group, were euthanized and subjected to necropsy. Bursal and Thymus indexes were calculated; histological sections were examined and scored; viral tissue distribution determined by qRT-PCR in the bursa of Fabricious (BF), thymus, kidney, cecal tonsils, spleen, proventriculus, harder gland and bone marrow. No clinical signs, nor mortality were recorded in any group dur-ing the study. BF of both inoculated groups showed enlargement and oedema in the acute phase of the infection (2 dpi), followed by atrophy, which lasted until the end of the trial. Microscopic lesions of the BF of ITA IBDV inoculated birds consisted in lymphocyte depletion, cystic cavi-ties and poor regeneration process. Viral RNA was persistently detected until the end of the tri-al in lymphoid tissues. The study showed that ITA genotype, though it has a subclinical course, causes a severe and persistent damage of BF, therefore, its circulation in broilers might be a threat for the poultry industry.