Rajasekhar R.Rajasekhar R.CHANDANKAR VAIDEHI DEORAOCHANDANKAR VAIDEHI DEORAO2022-10-202022-10-202021-04-162021-04-16https://krishikosh.egranth.ac.in/handle/1/5810189243Submitted in partial fulfilment of the requirement for the degree of Master of Veterinary Science in veterinary MicrobiologySubmitted in partial fulfilment of the requirement for the degree of Master of Veterinary Science in veterinary MicrobiologyInfectious bursal disease (IBD) is considered as menace as it affects poultry industry globally causing immunosuppression, high mortality and heavy economic loss. Outbreaks of IBD were reported in many states of India including Kerala. The present study was conducted to carry out molecular characterisation of VP1 gene of virulent IBDV in Kerala. Total 43 samples were processed for the detection and analysis of VP1 gene of IBDV. Out of 43 samples, 22 samples were positive for VP1 gene of IBD. The phylogenetic analysis of the partial VP1 gene sequences reveals the clustering of IBDV isolates into vvIBDV and non vvIBDV. Eighteen isolates (11 isolates from vaccinated flock and 7 from non-vaccinated flocks) clustered with very virulent strains. Four isolates (3 isolates were from vaccinated flock and one from non-vaccinated flock) clustered with non-virulent IBDV strains of classical virulent, classical attenuated and antigenic variant along with serotype 2 IBDV. The amino acid analysis of these 22 isolates revealed that 17 isolates possessed the characteristic vvIBDV TDN amino acid triplet while the four isolates had non vvIBDV NEG amino acid triplet at 145/146/147 position. The remaining isolate 1/CVASP/IBDV/VP1 shows unique PDN triplet instead of TDN. Two vvIBDV isolates (15/CVASP/IBDV/VP1 and 18/CVASP/IBDV/VP1) showed 100 per cent nucleotide and amino acid similarity with IL4 strain which is an attenuated very virulent vaccine strain. Four vvIBDV isolates showed neutral amino acid substitution K251R which was earlier reported in Indian strains. The novel amino acid substitution observed in our study were neutral E269D amino acid substitution in 12 isolates, neutral amino acid substitution T329S in five isolates, neutral T174N and non-polar to polar amino acid substitution A178T in isolate 10/CVASP/IBDV/VP1, non-polar to polar amino acid substitution P360R in isolate 17/CVASP/IBDV/VP1 and non-polar to polar amino acid substitution P188S in isolate 1/CVASP/IBDV/VP1. These novel mutations in our study reveals that evolution of vvIBDV occurred by genetic drift. The isolate 2/CVASP/IBDV/VP1 from non-vaccinated flock shows VP1 gene of non-vvIBDV, but possessed VP2 of vvIBDV type, indicates this is evolved by genetic shift of segment A and B. This is the first genetic characterisation study of field VP1 gene of IBDV isolates in Kerala, India.Infectious bursal disease (IBD) is considered as menace as it affects poultry industry globally causing immunosuppression, high mortality and heavy economic loss. Outbreaks of IBD were reported in many states of India including Kerala. The present study was conducted to carry out molecular characterisation of VP1 gene of virulent IBDV in Kerala. Total 43 samples were processed for the detection and analysis of VP1 gene of IBDV. Out of 43 samples, 22 samples were positive for VP1 gene of IBD. The phylogenetic analysis of the partial VP1 gene sequences reveals the clustering of IBDV isolates into vvIBDV and non vvIBDV. Eighteen isolates (11 isolates from vaccinated flock and 7 from non-vaccinated flocks) clustered with very virulent strains. Four isolates (3 isolates were from vaccinated flock and one from non-vaccinated flock) clustered with non-virulent IBDV strains of classical virulent, classical attenuated and antigenic variant along with serotype 2 IBDV. The amino acid analysis of these 22 isolates revealed that 17 isolates possessed the characteristic vvIBDV TDN amino acid triplet while the four isolates had non vvIBDV NEG amino acid triplet at 145/146/147 position. The remaining isolate 1/CVASP/IBDV/VP1 shows unique PDN triplet instead of TDN. Two vvIBDV isolates (15/CVASP/IBDV/VP1 and 18/CVASP/IBDV/VP1) showed 100 per cent nucleotide and amino acid similarity with IL4 strain which is an attenuated very virulent vaccine strain. Four vvIBDV isolates showed neutral amino acid substitution K251R which was earlier reported in Indian strains. The novel amino acid substitution observed in our study were neutral E269D amino acid substitution in 12 isolates, neutral amino acid substitution T329S in five isolates, neutral T174N and non-polar to polar amino acid substitution A178T in isolate 10/CVASP/IBDV/VP1, non-polar to polar amino acid substitution P360R in isolate 17/CVASP/IBDV/VP1 and non-polar to polar amino acid substitution P188S in isolate 1/CVASP/IBDV/VP1. These novel mutations in our study reveals that evolution of vvIBDV occurred by genetic drift. The isolate 2/CVASP/IBDV/VP1 from non-vaccinated flock shows VP1 gene of non-vvIBDV, but possessed VP2 of vvIBDV type, indicates this is evolved by genetic shift of segment A and B. This is the first genetic characterisation study of field VP1 gene of IBDV isolates in Kerala, India.EnglishThesis