Effect of a rapid heat treatment on Thai QX-like infectious bronchitis virus and evaluation of protection induced by a heat-treated virus

Abstract

The purpose of this study was to evaluate the effect of a rapid heat-treatment method on Thai QX-like
infectious bronchitis virus (IBV) and the efficacy on protection from the virus after heat treatment. QX-like IBV isolate
THA46 was incubated at 56 oC. The incubated virus was collected every 5 min for up to 1 h and then they were
inoculated into embryonated chicken eggs. At 6 days post-inoculation, allantoic fluid was harvested from the
embryonated eggs which were inoculated with virus of the longest heat-treatment time that induced lesions in the
embryos. That allantoic fluid was used in a subsequent round of heat treatment followed by inoculation into
embryonated eggs. The procedure was repeated eight times. The longest heat-treatment time at 56 oC that induced
lesions in the embryos for Thai QX-like IBV varied from 30 to 60 min. S1 and N genes of the virus after each heattreatment time were sequenced and none of the nucleotide changes were found. The efficacy of the heat-treated virus
was investigated by immunizing chicks at 1 and 14 days of age and challenging with the pathogenic isolate THA46 at
28 days of age. The results showed that virus detection in the tracheas, the gross lesion score of the tracheas and the
histopathologic lesion score of the tracheas and kidneys of the chickens immunized with heat-treated virus were
significantly lower (p<0.05) than those of the positive control group. The study demonstrates that a rapid heat-treatment
method has no effect on the S1 and N gene of IBV isolate used in this work. A heat-treated Thai QX-like IBV provided
a good protection against challenge with pathogenic Thai QX-like IBV.