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|Title:||Structural analysis of Infectious bursal disease virus isolates from clinical cases in vaccinated and unvaccinated birds|
|Publisher:||Department of Microbiology, College of Veterinary and Animal Sciences, Mannuthy|
|Abstract:||Field cases with history suggestive of infectious bursal disease (IBD) were screened for confirmation by Agar gel diffusion test (AGDT), using reference antigen and antisera received from Madras Veterinary College. From the positive cases, 4 isolates, two each from unvaccinated (PKD, EKM) and vaccinated (THR, KAN) flocks and an avirulent vaccine strain (VAC) were used for structural analyses and antigenic relationship studies. The percentage of mortality of the embryos infected by these strains ranged between 50 – 100 per cent, during the third and fifth day of inoculation, in the fourth passage. The lesions produced were cutaneous haemorrhages all over the body, congestion and thickening of CAM. Enlarged bursa and typical yellowish green discolouration of liver with brown patches were also noticed. All the five isolates were propagated in chicken embryo fibroblast culture, in which cytopathic changes characterised by rounding and subsequent detachment was seen from the third passage onwards. The chicks infected with field isolates revealed mildclinical symptoms. The lesions noticed after sacrificing them on the third day were moderately swollen gelatinous bursa with slight haemorrhage in some of them. Chicks that received vaccine strain revealed only mild lesion. The viral strains by SDS – PAGE revealed that all the field isolates contained nine identical polypeptides with molecular weights of 86 KD (VP2), 77 KD (VP4), 73 KD (VP5), 62 KD (VP6), 52 KD (VP7), 47 KD (VP8), 39 KD (VP10), 36 KD (VP11) and 32 KD (VP12). The vaccine strain resolved 11 peptides of whichthree, namely VP1 (93 KD), VP3 (80 KD) and VP9 (43 KD), were absent in the field isolates, but it lacked VP7 (52 KD). Mild difference in the molecular weights of VP6 and VP12 were also noticed between the field isolates and vaccine strain. Nucleic acid analyses in agarose gel showed two bands for all the five isolates without any difference in their migration pattern. Antigenic relationship of the IBDV isolates was studied by AGDT, CIE and IE. All the four isolates produced only one precipitation line against the antiserum and this precipitation line was identical to the one produced by the vaccine strain. From the observations made, the possible reasons for breakdown of immunity and a schedule of vaccination to overcome this situation have been discussed.|
|Theme:||Infectious Bursal Disease Virus Ispolates|
|Appears in Collections:||Theses|
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