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Abstract
Infectious bronchitis (IB) is a worldwide respiratory disease of major economic importance associated with losses from production inefficiencies and mortality. Live and inactivated oil emulsion vaccines have been used in IB immunization programs. Although commercial live vaccines have been attenuated, respiratory reactions are commonly observed after vaccination. Replication of infectious bronchitis virus (IBV) in several tissues causes particular lesions. However, in the intestines, viral replication has not been associated with clinical manifestations or microscopic changes. Several IBV strains have been passaged in the intestinal tract using developed in vivo and in vitro systems to decrease not only their presence, but also their effects on the upper respiratory tract while still causing no lesions on the intestinal tract. One of the intestine passaged IBV strains, an Arkansas serotype, exhibited a lower presence and effect on the tracheal epithelium than an attenuated Arkansas vaccine. The milder lesions produced by the intestine passaged IBV strain could decrease the invasion and multiplication of secondary pathogens constantly present in chicken houses, decreasing their negative economic impact. The use of the highly attenuated IP-Ark 1 strain in vaccination programs should be considered. The development of vaccination programs is based on the determination of IBV strains causing the disease in the field. However, the constant presence of new IBV serotypes or variants complicates the control of the disease. In 2003, the presence of respiratory disease with high morbidity and mortality in commercial layers and broilers intensively vaccinated with the Massachusetts 41 strain was observed in Colombia. The presence of IBV in phenol-treated allantoic fluid samples obtained from broilers and commercial layers was initially determined by amplification of the N gene by reverse transcriptase-polymerase chain reaction (RT-PCR). Specific primers were designed to amplify the S1 gene of some of the Colombian IBV isolates. Further molecular characterization by RT-PCR followed by nucleotide sequencing of the HVR 1 of the S1 glycoprotein gene was performed. This study revealed for the first time the presence of four indigenous genotype clusters genetically distinct to the Mass 41 strains. This finding might indicate a low or no protection offered by the currently used Mass 41 vaccine against field isolates.