Infectious bursal disease: outbreak investigation, molecular characterization, and vaccine immunogenicity trial in Ethiopia

Abstract

The study was conducted with the objective of isolation and molecular characterization of infectious bursal disease virus (IBDV) circulating in Ethiopia and to assess the immunogenicity of different commercially available live attenuated IBD vaccines and finally to select the appropriate vaccine strain for the existing IBDV. Outbreak samples collected from different poultry farms with IBD infection between 2013 and 2015 were used for the virus isolation and molecular characterization. IBD vaccine immunogenicity test was conducted using four different commercially available live attenuated IBD vaccine strains: namely D78, B2K, LC75, and EXTREM. Day-old Bowman brown chickens purchased from commercial farm in Debre Zeit were used for the experiment. Serum samples were collected at days 14 and 21 and screened for the presence of maternal IBDv antibodies. The screening test result revealed that most of the chickens from vaccinated progeny were positive at the age of day 14 with mean antibody titer of .42, but declined at day 21 to 0.049 below cut-off point (S/P < 0.3). Chickens were divided into five different groups (four vaccinal and one control) and vaccinated at the age of day 21 and boosted after 14 days. Serum samples were collected and all of them were challenged at their 42 days of age with locally isolated very virulent infectious bursal disease virus (vvIBDV). From four of the vaccine strains used for immunogenicity study, the intermediate plus strains (LC75 and EXTREM) found to be superior and efficiently cross protect against the challenge with locally isolated vvIBDV. The development of clinical signs was studied and post-mortem examinations were conducted both on dead and sacrificed birds. From a total of 25 tissue samples processed for virus isolation on chicken fibroblast cell culture, 95% (18/20) of bursa and 80% (4/5) of the spleen samples showed visible cytopathic effect (CPE). The positive samples were tested by PCR and 19 of them had the expected band (643 bp). Further 11 representative samples were sequenced and confirmed that the circulating virus among poultry population in the country is vvIBDV. The study has recommended to produce vaccine using intermediate plus strains to prevent and control currently circulating vvIBDV.

Sequence-based comparison of field and vaccine strains of infectious bursal disease virus in Ethiopia reveals an amino acid mismatch in the immunodominant VP2 protein

“…Understanding its epidemiology is important for optimal control using vaccines, and it is necessary to catalogue the strains circulating in the country. Based on the criteria used to identify very virulent IBDV (vvIBDV), mortality rates, nucleotide and amino acid sequences at key positions, and their phylogenetic position, the field strains isolated in this study are genotypically very virulent, which can break the high and normally protective [18], when vvIBDV caused several outbreaks in Ethiopia. Taken together, the results should be taken as an alarm for the livestock service authorities.…”

Immunogenicity and Efficacy Evaluation of Vero Cell-Adapted Infectious Bursal Disease Virus LC-75 Vaccine Strain

“…5 Since then, the circulation of very virulent and/or classical virulent IBD viruses were reported from different parts of Ethiopia. 6 , 7 …”

Gross, Histopathological, Histoenzymatic and Histochemical Studies on Infectious Bursal Disease in Broiler Chickens

“…Our observations are found to be in accordance with the earlier reports of Rashid et al (2013) and Preeti et al (2018). However, the presence of concurrent infection of IBD and Coccidiosis in one of the groups is most probably attributed to the immunosuppressive effect of virus which results in the flaring up of secondary infections (Murmu et al,2014) or can also be due to mild immunosuppressive effect of vaccine as earlier explained by Mekuriaw et al (2017).…”