Efficacy of Live H120 Strain against Variant Genotype Infectious Bronchitis Virus Isolated in Thailand in Broiler Chickens

Abstract

This study investigated the level of protection generated by vaccination with a live attenuated infectious bronchitis virus (IBV) vaccine, H120 strain against variant genotype IBV isolated in Thailand. Sixty 1-day-old female broiler chickens were randomly divided into 4 groups of 15 chickens each. The chickens in Group 1 were vaccinated at 1 day old, whereas the chickens in Group 2 were vaccinated at 7 days old. Groups 3 and 4 did not receive IBV vaccine and served as positive and negative control groups, respectively. At 21 days of age, the chickens in Groups 1-3 were individually challenged with 104.8 EID50 of variant genotype IBV (isolate THA90151). Protection was evaluated at 7 days post-inoculation. Results revealed that the clinical signs, histopathological lesion score of the trachea, ciliostasis score and infection rate of the tracheas and kidneys of the vaccinated chickens were lower than those of the non-vaccinated, challenged control chickens. These results suggest that vaccination with live IBV vaccine, H120 strain can induce a certain level of protection for broiler chickens challenged with a variant IBV strain isolated in Thailand.