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

Abstract Background: Infectious bursal disease virus (IBDV) is an avian viral pathogen that causes infectious bursal disease (IBD) of chickens. The disease is endemic in Ethiopia since 2002 and vaccination is the major means of disease prevention and control. IBD vaccine is produced in Ethiopia using primary chicken embryo fibroblast (CEF) cell; which is time-consuming, laborious, and uneconomical. The present study was carried out to develop cell-based IBDV LC-75 vaccine using Vero cells, and to evaluate the immunogenicity and protection level.Results: Identity of the vaccine seed was confirmed using gene-specific primers using reverse transcription polymerase chain reaction. Confluent monolayer of Vero cells was infected with vaccine virus and serial passage continued till passage ten. Characteristic virus induced cytopathic effect was observed starting from passage 2 on the third day post-infection. The infectious titer of adapted virus showed a linear increment along the passage level. Virus induced specific antibody was determined using indirect ELISA after vaccination of 14 days old chicks through ocular route. Accordingly, the antibody titer measured from Vero cells vaccinated chicks revealed similar level with the currently available CEF cell-based vaccine. Chicks vaccinated with Vero cell adapted virus showed complete protection against very virulent IBDV, while unvaccinated group had 60% morbidity and 25% mortality.Conclusions: The IBDV vaccine strain well adapted on Vero cells and found to be immunogenic induces antibodies development and successfully protects chicks against challenging with the circulating field IBDV isolate. Hence, it is recommended to produce IBD vaccine using Vero cell culture with enough quantity to conquer the limitations using CEF cells and thus to vaccinate chicks to protect against IBDV infection.