Pathogenicity and Effects on Lymphoid Organs of Recent Moroccan Very Virulent Infectious Bursal Disease Virus in Broilers and SPF Chickens

The aim of the current study is to evaluate the pathogenicity of recent infectious bursal disease virus (IBDV) (1/chicken/Morocco/IB19/2017) genetically characterized as vvIBDV belonging to genogroup 3.Two chicken lines, broiler and specific-pathogen-free (SPF) chickens, were inoculated by occulonasal route with 0.2 ml of the 105EID50 /ml of viral solution of IB19 vvIBDV strain at 29 days of age. The experimental monitoring was carried out during 10 days post challenge (dpc). The clinical signs stared on day 2 pc with maximum severity observed between 3 and 6 dpc. The total mortality rate reached 10% in broilers (group G1) and 93% in SPF (G3). The macroscopic lesions in broilers G1 was a marked hypertrophy of the bursa of Fabricius (BF) with slight haemorrhage observed between 2 to 4 dpc, followed by very pronounced atrophy observed on the 5 dpc. The post-mortem examinations of dead SPF birds (G3) revealed on 3 dpc very haemorrhagic BF with black cherry appearance in 80 % of dead birds. The mean Bursa/Body Index (BBI) of challenged broilers (G1) showed a decrease of 46% on day 9 pc compared to broilers control group (G2) indicating bursal atrophy. The microscopic lesions found in the BF on 3 dpc consisted mainly of inflammation with severe lymphoid depletion of the follicles. The evaluation of recent vvIBDV outbreak is very important to understand its epidemiology and will contribute to the efficient prevention and control of IBD.