Genotypic And Serotypic Characterization Of Infectious Bronchitis Virus Of Chickens
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Date
2006
Journal Title
Journal ISSN
Volume Title
Publisher
Tamil Nadu Veterinary and Animal Sciences University
Abstract
A total of 161 samples were screened for the presence of IBV genome by ‘N’
gene nested RT-PCR and twenty four were positive. All the positive samples on
further passages revealed IBV specific lesions such as dwarfing of embryos with
curled toes in ECE. A part of the S1 gene (220 bp) could be amplified by RT-PCR in
22 out of 24 'N' gene RT-PCR positive samples. For eight field isolates, the 5’ end
(600 bp) and 3’ end (464 bp) of S1 gene were amplified and sequenced. In addition,
the 5' end of two isolates, Ind/KA/151/05 and Ind/Hy/152/05 were sequenced using
the 600 bp product while the 3' end of two other isolates, Ind/KA/135/04 and
Ind/Hy/154/05 were sequenced using the 500 bp (outer) or 400 bp (nested) product.
On sequence analysis all the twelve isolates were found to belong to Mass 41
genotype. On comparison with the vaccine strain, H120, sequence homologies of the
field isolates ranged from 87.9 to 95.9 per cent for the 5’ end of ‘S1’ gene and 90.7 to
98.9 per cent for the 3’ end of ‘S1’ gene. The analysis of HVR I, II and III sequences
revealed that the field isolates were less homologous with vaccine strain, nucletide
homologies ranging from 70 to 100 per cent. The d s / d ns ratio for 80 per cent of the
sequenced field isolates was less than 1.0.
The serotype of five isolates (Ind/TN/92/03, Ind/TN/97/03, Ind/114/03,
Ind/KA/135/04 and Ind/KA/136/04) was determined by cross neutralization test using
homologous and heterologous sera. All were found to belong to Mass 41 serotype.
In vivo challenge (protectotypic) experiments, demonstrated the ability of the
most commonly used vaccine H120, to induce protection against five field isolatestested. Birds vaccinated with H120 and challenged with the field isolate,
Ind/TN/92/03 showed the lowest protection score. The pathotypic trial revealed that
the isolate, Ind/TN/92/03 also had the highest lesion score (25.0) and hence was
considered as the virulent Mass 41 virus.
A live attenuated vaccine was prepared by passaging the isolate Ind/TN/92/03,
twenty five times in ECE. The live attenuated vaccine afforded protection to
homologous challenge in 3 week old chickens equal to that of the commercial
H120 vaccine.
The inactivated vaccine was also produced from the same isolate. The
inactivation was done by formalin and the inactivated virus was mixed with oil
as adjuvant. The inactivated also produced good ELISA titre in live attenuated
vaccine primed but not in unprimed birds
Description
Keywords
IBV, genotype, serotype, protectotype, pathotype, live attenuated, killed vaccine