Detection of infectious bronchitis virus strains similar to Japan in Taiwan

TSAI, Cheng-Ta; TSAI, Hsin-Fu; WANG, Ching-Ho

The present investigation might have under-estimated the actual prevalence, because we only sampled tracheas for virus detection. IBV can be detected in the trachea during the first 3 to 5 days post-infection. After this period, the virus titer falls quickly in the second week [6] . We may have missed the acute infection stage when sampling slaughterhouses due to the elapsed time between the beginning of the infection and sampling. Indeed, the present prevalence is lower than that reported in previous studies in the United Kingdom and Jordan [10, 13] . The prevalence in those studies reached about 60%, because the sampled chickens exhibited respiratory signs of infection or IB was suspected during sampling. In the present investigation, the broilers may have been healthy, because they reached market age for the slaughterhouses. The phylogenetic tree constructed using the N gene sequences is shown in Fig. 1 . The Taiwanese strain could be distinguished from the other IBVs using this N gene. However, this segment could not be used to separate the Taiwan strain into its different groups, TW-I and TW-II. In order to distinguish TW-I from TW-II, we used primers located at the 5′ terminus of the S gene, and the resulting phylogenetic tree could distinguish between TW-I and TW-II (Fig. 2) . There were more TW-II samples than TW-I samples in this investigation. The S1 and S7 isolates might be from the 4/91 vac-cine strain, because they were very similar (Figs. 1 and 2) . The S36, S75, S76 and S77 isolates were from another vaccine, H120, commonly used in Taiwan.