AVIAN CORONAVIRUS IN EGYPT: EPIDEMIOLOGICAL ACUITIES AND PATHOGENICITY IN COMMERCIAL BROILER CHICKENS
Infectious bronchitis virus (IBV), a gamma coronavirus, is responsible for a highly contagious disease in chickens resulting in substantial economic losses to the poultry industry around the world. The emergence of new types of IBVs is considered one of the major concerns regarding to IB. A preliminary diagnosis of IB was made based on the flock history and the characteristic pathologic findings. In the current study, we investigated the outbreaks of respiratory signs and diarrhea in broiler chickens (n=77) between 2014 and 2018. Upon necropsy, the affected chickens showed tracheal and kidney lesions, suggestive of IBV. The IBV was detected in 33 farms using real-time reverse transcription-PCR, targeting the nucleocapsid gene. Investigation of IBV among vaccinated chickens would considerably ameliorate the present immunization programs and support the development of more effective vaccines. The IBV was detected in vaccinated birds (45.8%). The virus was isolated in fertile chicken eggs, which revealed embryonic mortality (20-40%) within 5-7 days after the 3rd passage, small embryos or dwarfing up to 30.2% versus non-inoculated ones. Virus pathogenicity was determined experimentally in 7-day-old broiler chickens inoculated oculo-nasally with 104 median embryo infective dose. The infected birds experienced severe respiratory signs, diarrhea and tracheal and renal lesions. The virus displayed a wide range of tissue tropism, particularly in the trachea, lungs and kidneys, and was shed via the respiratory tract and cloaca. The results emphasized the significance of conducting a comprehensive surveillance of IBV infections among chicken flocks in Egypt and provide significant insights into the virulence properties of IBV. Further studies of nucleotide sequence analysis of circulating IBV strains and evaluation of vaccine efficacy are needed.
Keywords: IBV, RT-PCR, Pathogenicity, Clinical scoring, Histopathology, Nephropathogenic strain