Outbreak Investigation and Molecular Characterization of Infectious Bursal Disease Virus in Poultry Farms at Modjo and Bishoftu Towns, Central Ethiopia

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Infectious Bursal Disease (Gumboro disease) is a highly contagious viral disease of chickens with a worldwide prevalence, which is caused by infectious bursal disease virus, (genus Avibirnavirus, family Birnaviridae), infects chickens and is becoming serious threat and challenging to the emerging poultry industry in Ethiopia. Molecular characterization targeting the major capsid protein, viral protein 2, plays an important role in the identification of the various strains of infectious bursal disease virus, tracing back of the origin of the virus and in vaccine matching studies. An outbreak based cross sectional study was carried out from October 2019 to May 2020, with the main objectives of characterizing field strains of the virus from outbreak cases in poultry farms at Bishoftu and Modjo towns, Central Ethiopia. A total of six farms were addressed during the study time and four to five chickens were opened per outbreak from each farm. Smear samples for molecular analysis and pooled samples for culture were collected on Flanders Technology Associates cards and in universal bottles containing viral transport medium, respectively. Virus isolation and reverse transcriptase-polymerase chain reaction and sequencing were performed to confirm the outbreak cases. Bursal suspensions were prepared for both cell culture and molecular analysis. Up on visualizations of the DF-1 cell lines used for cell culture after two passages, cytopathic effects: cell swelling, cell rounding, detachment and floating, were observed. Up on characterization of viral protein 2 region of the virus using reverse transcriptase polymerase chain reaction and sequencing, both vaccinal (six IBDV Genogroup 1) and field viral strains (five IBDV Genogroup 3) were detected. The current isolates made three clusters, namely, isolates identical to vaccinal strains ((Winterfield 2512-like) - CEVAC® IBD L)) and (Faragher 52/70 used in HVT+IBD vaccines), field strains identical to very virulent strains deposited in the Genbank, and isolates identical to vaccine strain manufactured and marketed by National Veterinary Institute, Ethiopia. The results indicate that, in addition to the continuous circulation of vvIBDV strains in the country, vaccinal strains are also reverting to their virulence being one of the causes for the investigated outbreaks. Therefore, further and sustained molecular characterization of the vaccinal and field IBDV strains is crucial as the virus is resistant and prone to change in its nucleotide sequences.



Bishoftu, IBDV, Infectious bursal disease, Modjo, Molecular characterization, Outbreak investigation