Histopathological study of respiratory tract in chickens following vaccination against infectious bronchitis virus (H120)

Using the infectious bronchitis vaccine by spraying method can result to respiratory complications in chickens. The aim of the present study was to histopathological evaluate of the respiratory system of chickens following vaccination against infectious bronchitis virus with live attenuated vaccine (Massachusetts serotype) via spraying method. For this purpose, sixty one-day-old chickens – free of Mycoplasma gallicepticum and Mycoplasma synoviae – were randomly assigned into 2 equal groups and 3 subgroups determined for each. The chickens of treatment group were vaccinated at the first day of experiment. The management condition and feeding was equal for both groups. Treatment subgroups along with their counterpart control subgroups were necropsies at the 5th and 10th days of experiment, respectively. Trachea and lungs of the experimental chickens were separated for microscopic evaluations, as histological sections were prepared routinely. Microscopically, damages of the trachea and bronchial epithelium and mucosa along with parenchyma of the lungs assessed and compared between the subgroups. Significant differences between the subgroups were determined by Mann Whithney U test. There were significant differences between treated subgroup at the day 10 with all of the control subgroups (p<0/05). There were also significant differences between treated subgroup at the day 21 and the control subgroups (p<0/01). Furthermore, there was significant difference between treated subgroups at the days 10 and 21 of experiment (p<0/05). No significant differences determined between treated subgroup at the day 5 and the control subgroups. The results showed that vaccination against infectious bronchitis virus (H120) with live attenuated vaccine (Massachusetts serotype) by spray results in histopathological damages of respiratory system in chickens.