Infectious Bursal Disease Viru : Outbreaks Investigation, Molecular Characterization and Development of Live Attenuated Vaccine Using Local Isolates
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Date
2012-04-15
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Addis ababa Universty
Abstract
This study was conducted on sample collected from different regions of the country, where infectious bursal disease (IDB) outbreaks were reported. Samples were processed both at National Veterinary Institute and University of Liverpool, United Kingdom, with the aims of molecular characterization of local isolates, analyzing genetic relatedness of IDB virus circulating in the country with currently produced vaccine and development of vaccine from local isolates. The nucleotide and deduced amino acid sequence for VP2 hypervariable region (HVR) of ten IBDV isolates collected from 2009 until 2011 was also determined by RT-PCR and sequencing, and compared with well characterised IBDV isolates worldwide. A total of 136 bursa sample were pulled into 44 samples. Bursa samples were processed and cultured onto both confluent primary CEF cell cultures as well as fully confluent established cell line (Vero). Viruses were isolated from 41 (93 .2%) samples out of the 44 pulled samples. All the (Vero). Viruses were isolated from 41 (93 .2%) samples out of the 44 pulled samples. All the isolates were grown and able to demonstrate CPEs on CEF cell cultures on the first passage Phylogenetically, Ethiopian IBDV isolates were from one of two genetic lineages: very virulent lBDV and variants of the classical attenuated vaccine strain (078). Nucleotide identity between Ethiopian vvIBDVs range between 0% to 2.6% over VP2 HVR. isolate was superior to the current commercially available vaccine. The adapted trial vaccine isolate was superior to the current commercially available vaccine. The adapted trial vaccineEthiopian vvIBDVs clustered phylogenetically with the African IBDV genetic lineage, independent of the Asian/European genetic. This indicates the circulating of vvIBDV among Ethiopian chickens. Classical variant strain (IBDV 06/10) was selected for adaptation trial using Vero cells. The 9th Vero passage local isolate was evaluated with the current NVI vaccine for immunogenicity and pathogenesity on chicken. The result showed that the adapted local isolate was superior to the current commercially available vaccine. The adapted trial vaccine induced significantly (P<0.05) higher mean antibody titre (3281.35± 101.43) compared to the cun'ently used vaccine strain (2784.12±92.34). The mean bursa weight from the unvaccinated control groups was 20.8±1.2 g while it was 3.6±O.l6g and 2.8±0.07g, respectively, for commercial vaccine and 9th passaged local isolate. Although the difference in the mean bursa weight between the vaccinated groups was not statistically significant (P>0.05), the difference in the mean bursal weight between control and vaccinated groups was statistically significant (P<0.05).
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Keywords
Infectious bursal disease, Outbreak investigation, molecular characterization