MOLECULAR DETECTION AND CHARACTERISATION OF INFECTIOUS BURSAL DISEASE VIRUS (IBDV) IN POULTRY
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Date
2019-07-15
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COLLEGE OF VETERINARY AND ANIMAL SCIENCES, POOKODE WAYANAD
Abstract
Recurrent infectious bursal disease (IBD) outbreaks were reported in different
regions of Kerala, India. This study reports the molecular detection and comparative
genetic analysis of the hypervariable region of the VP2 gene of IBD virus from the
field outbreaks in Kerala. Genetic analysis of 22 isolates from 41 suspected field
outbreaks of IBD were carried out in this study. In phylogenetic analysis, the
obtained field isolates fall into genogroup 1 and 3. In genogroup 3, all vvIBDV
isolates shared a common ancestor with other south Indian isolates but isolates
9/CVASP/IBDV, 10/CVASP/IBDV, 12/CVASP/IBDV, 14/CVASP/IBDV and
17/CVASP/IBDV are most recently evolved and is diverged from the south Indian
isolates and other isolates obtained in the study. The amino acid sequence of 22
isolates were analysed, out of which 18 had serine rich heptapeptide virulence
sequence ‘SWSASGS’ and conserved amino acids which are characteristic of
vvIBDV. In all the vvIBDV isolates obtained in the study had phenylalanine and
Valine at the position 240 and 294 respectively similar to recently evolved Indian
IBDV isolates. But we observed T269A and S299N mutations in the isolate
6/CVASP/IBDV and is the first report of such mutations at this positions in India
IBDV isolates. The isolate 11/CVASP/IBDV had a unique mutation of V225A which
is not yet reported in IBDV isolates. Among these 18 isolates, 9 isolates obtained
from vaccinated flocks. Two isolates (15/CVASP/IBDV and 18/CVASP/IBDV) were
similar to intermediate plus vaccine strain. The isolates 8/CVASP/IBDV and
19/CVASP/IBDV had amino acids unique for the intermediate vaccine with
mutations observed at H253Q and V256I in 19/CVASP/IBDV, T270A and novel
mutation N279Y in isolate 8/CVASP/IBDV. These two isolates had non-virulent
classical heptapeptide sequence ‘SWSARGS’ nevertheless they produce field
outbreaks of IBD. This is the first genetic characterisation study of field IBDV
isolates in Kerala, India