EFFICACY AND SAFETY OF ATTENUATED LIVE INFECTIOUS BRONCHITIS VIRUS STRAIN QX-LIKE IN CHICKENS
Résumé
The attenuation of IB QX-like virus strain IB L1148 is described. The virus was passaged multiple times in embryonated specific pathogen free (SPF) chickens eggs and at different passage levels samples were tested for safety for the respiratory tract and kidneys in one day old SPF chickens. There was a clear decrease in pathogenicity for the respiratory tract and kidneys, when the virus had undergone a large number of passages. Passage level 80 was investigated for safety for the reproductive tract in one day old SPF chickens and 7 days old SPF chickens. In one day old chickens 12.5% of the vaccinated animals had macroscopical lesions. No lesions were observed if the chickens had been vaccinated at 7 days of age. Passage level 80 was investigated for its ability to spread from vaccinated to non-vaccinated chickens and for dissemination in the body. The virus was able to spread from vaccinated chickens to groups of non-vaccinated chickens, and in the vaccinated animals the virus was found very frequently in laryncheal and cloacal swabs. A fragment of the hypervariable region of the S1 protein of passage level 80 was sequenced and there were nucleotide substitutions resulting in 2 substitutions on the level of the amino acids. Passage level 80 Passage level 80 was given 2 and 5 additional passages, i.e. passage levels 82 and 85, respectively. Both passage levels were tested as vaccine in SPF chickens and passage level 85 was tested as vaccine in commercial chickens with MDA against a challenge with QX-like strain IB D388. In SPF chickens as well as in chickens with MDA the vaccines based on strain IB L1148 were efficacious against the challenge.
Domaines
Biologie animale
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