Iraqi Journal of Veterinary Sciences, Vol. 36, No. 1, 2022 (171-175) 171 Iraqi Journal of Veterinary Sciences www.vetmedmosul.com Genotyping of avian infectious bronchitis virus in broiler farms in Duhok province, north of Iraq R.H. Isa 1 , J.M. Abdo 2 , and Y.M. Al-Barzinji 3 1 Animal Production Department, College of Agricultural Engineering Sciences, 2 College of Pharmacy, University of Duhok, Duhok, 3 Animal Resources Department, College of Agricultural Engineering Sciences, Salahaddin University, Erbil, Iraq Article information Abstract Article history: Received February 28, 2021 Accepted May 20, 2021 Available online November 23, 2021 Infectious bronchitis disease is becoming the most challenging disease in broiler fields in Iraq. This disease leads to massive economic loss every round of production. Three vaccine strains H120, Ma5, and 4/91 are used to combat the disease during the production period while outbreaks occur continuously. This study aimed to investigates the prevalence and circulation of Mass and 4/91 IBV strains in the broiler fields in Duhok province which is the first record in the area. Positive samples were obtained from suspected flocks to this disease during 2018-2020. A specific region of S1 was amplified using specific pairs of primers. Genotyping was performed by nested PCR using specified primers for detecting both Mass and 4/91 strains. In the results, all of the positive flocks were infected with nephropathogenic strain 793/B or 4/91. Two of the positive flocks had an infection with both Mass and 4/91. These results indicate that more than one strain circulates in the area as well as shows the weakness of vaccines used in broiler fields. Keywords: Broiler Infectious bronchitis Duhok Iraq Nested RT-PCR Correspondence: R.H. Isa renas_kurd2003@uod.ac DOI: 10.33899/ijvs.2021.129635.1670, ©Authors, 2022, College of Veterinary Medicine, University of Mosul. This is an open access article under the CC BY 4.0 license (http://creativecommons.org/licenses/by/4.0/). Introduction Avian Infectious bronchitis disease (IB) is one of the most challenging diseases in the poultry industry. Chicken is exposed to IBV through its entire lifespan (1). Massive economic loss is due to the fast and rises emergence of novel variants or serotypes in both broiler and layer flocks (2). Morbidity reaches 100% with a mortality of 20-30% (3) while secondary infection may increase flock mortality (4). Moreover, the upper respiratory tract, kidney, digestive tract, and ovary are the main infection sites of this virus. Clinical symptoms are difficulty in breathing, plaque in the trachea and/or bifurcation, ovary damage, kidney swelling, and sneezing (2). The main consequences are weight loss, drop in egg production, and mortality (1). Although no vertical transmission has been claimed (5), it is transmitted horizontally such as direct and indirect chicken contact and air-born route (contamination and poor field biosecurity). Although successful vaccination is considered one of the best methods for immunizing the birds from this disease, genotyping the field strain may determine the vaccine strains that should be applied (6). Genomic deletions, insertions, substitutions, point mutations, and RNA recombination of the S1 gene are associated with the emergence of new variants (7). The S1 is responsible for viral attachment to the host cell receptors. Additionally, there are three hypervariable regions in the structure of this gene. For these reasons, this gene has been the preferable region for genotyping this virus by many researchers (8). Different serotypes of newly evolved variants from chickens may cause partial or complete vaccination failure (5,9). In Iraq, the first report on this disease was made by (10). Later, the isolation and identification were performed for a specific isolate AM 88 by (11). However, the use of three inactivated and/or live-attenuated IBV vaccines H120, Ma, and 4/91 couldn’t stop the massive economic loss in the Iraqi poultry industry due to continuous outbreaks of this disease (12). In the south and middle of Iraq, studies on this disease have been performed to genotype this infection agent (13). The new variant, Sul/01/09 (GQ281656) has