Objective: Infectious bronchitis virus is a coronavirus that causes respiratory, reproductive, urinary and gastrointestinal lesions in infected chickens. Mortality and reduced production are two major economic losses caused by the disease. Due to lack of proofreading in RNA polymerase of the virus, mutation occurs frequently while virus replicate. Other than mutation, recombination is another method of sequence variation in the genome of the virus. Due to these phenomena several serotypes and genotypes have emerged. Sequence analysis of the hypervariable region of spike gene (S1) is frequently used for genotyping and serotyping of the isolates. In 1996, a new genotype named IBV-QX was recognized in China. Since then, QX and QX-like genotypes were reported in West and East Europe, South East and Central Asia, Middle East and Southern Africa. To our knowledge there is no published report of IBV-QX in this region. This abstract report the occurrence of Infectious Bronchitis disease caused by strain QX in layer farms of Mashhad city, located in North East of Iran Material and Methods: Since the last two years clinical presentation of false layer in some layer flocks of Mashhad, khorasan Razavi, Iran were observed. History of the flocks and clinical signs and macroscopic lesions were evaluated. The virus was isolated by inoculation of kidney and cecal tonsil homogenates into CAM of 8-11 days old embryonated chicken eggs. After serial passages, the defects in embryos were evaluated and viral RNA was extracted from alantoic fluids. Viral RNA was subjected to RT-PCR assay using primers specific for: IBV species, IBV-QX strain and S1-hypervariable sequencing primers. Results and Conclusion: Lack of optimum peak and signs of penguin-like posture and pendulous abdomen in affected flocks along with the large cystic oviduct with clear watery fluids in necropsy were among the main clinical observation in the affected flocks. Lesions such as dwarfing, stunting, or curling of embryos were observed in embryos inoculated with infectious materials. The results obtained from RT-PCR by several primers confirmed the presence of IBV-QX strain in the flocks investigated. The data obtained in project will be presented in details in the congress.

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