Bekele, Takele (PhD)Mekuriaw, Aregitu2018-06-272023-11-082018-06-272023-11-082015-06http://etd.aau.edu.et/handle/123456789/4075Infectious bursal disease (IBD) is a highly contagious and economically important immunosuppressive viral disease of poultry that is found worldwide. The disease is caused by a dsRNA virus. This study was conducted in National Veterinary Institute from September 2015 to April 2015 on the objective of the isolation, identification and molecular characterization of infectious bursal disease virus (IBDV) on infectious bursal disease (IBD) suspected outbreak samples were collected from 2013 to 2015 from different parts in Ethiopia and to test the immunogenicity of four different live attenuated commercially available infectious bursal disease vaccines and also to select the appropriate infectious bursal disease virus vaccine through the selected different IBDV vaccine immunogenicity test and cross protection test against the local isolated VVIBDV challenge virus and also to determine the appropriate time of IBDV vaccine administering time on vaccinated progeny originated chickens. A representative outbreak samples were employed for virus isolation (cell culture) on chicken fibroblast cell (CFC), molecular characterization (touchdown PCR) and PCR positive isolates subjected to further sequencing. On the other hand the IBDV vaccine immunogenicity test was conducted by employed the four different live attenuated commercially available infectious bursal disease vaccines strain: Namely (one mild intermediate strain - D78, one invasive intermediate strain - Bursine-B2k, and two intermediate plus or hot strain IBD LC75 and IBD EXTREM) and infectious bursal disease virus maternal antibody (IBDV MAb) free specific pathogen free (SPF) chickens of vaccinated progeny and also the recently local isolated very virulent infectious bursal disease virus (VVIBDV) as a challenge virus. The IBDV MAb was screened the experimental SPF chickens before administering the experimental IBDV vaccines. The chickens sera was collected and examined post 14 days of primary immunization, post 7 days of booster dose or prior to challenge test and also 21 days post challenge test serologically by flock IBDV antibody screening ELISA kit to compute the immunogenicity and cross protection capacity against the challenge locally isolated VVIBDV. Among the study objectives and criteria’s results were revealed as followed, Eighteen (95%) of bursa and four (80%) of the spleen samples suspensions were grown and develop visible cytopathic effect (CPE) on chicken fibroblast cell cultures (CEF), totally nineteen cell culture isolates (eleven 2013 and 2014 samples and seven 2015 samples) were revealed the expected VP2 gene amplified PCR band (645base pairs); the xiv eleven 2013 and 2014 positive PCR products sequence analysis were also confirmed the currently circulated IBDV were VVIBDV virus. On the other hand based on those computed parameters, the IBDV vaccine immunogenicity test studies were revealed that the IBDV vaccine administration appropriate scheduled on vaccinated progeny flocks should be at 21 and 35 days age for primary and booster dose vaccination respectively and also the superior immunogenic, potent and efficiently cross protective for recently local isolated VVIBDV was intermediate plus IBDV vaccine strain LC75. Therefore based on the above study results the following points were recommended producing this candidate live intermediate plus IBDV vaccine strain LC75 should be effective to prevent and control the currently circulated VVIBDV virus, commercial poultry farm owners should be screened the IBDV maternal antibody (MAb) of the flock before primary IBDV vaccine administration , and IBDV virus molecular epidemiology study with a planned interval should be conducted to assessed the antigenic diversity of the IBDV virus. Key words: Infectious Bursal Disease Virus (IBDV), IBD, IBDV vaccine, polymerase chain reaction, sequencing, IBDV maternal antibodyenInfectious Bursal Disease Virus(IBDVIBDIBDV vaccinepolymeraschain reactionsequencingIBDV maternal antibodyThesis