A study of natural co-infection caused by avian influenza (H9 subtype) and infectionbronchitis viruses in broiler chicken farms showing respiratory signs

摘要

Although H9N2 AIV( Avian Influenza Virus) is pathotypedas low pathogenic avian influenza virus, our extensive field experiences during the lastdecade show serious disease and high mortality associated with this subtype in many regionsof Iran. One of the possible explanations for such a high mortality and great economic lossescould be mixed infection with other respiratory pathogens such as infectious bronchitis virus(IBV). This investigation was conducted to study the natural infection of H9N2 AIV andinfectious bronchitis viruses, and to determine if co-infections occur in broiler chicken flocksin Fars province, Iran. The tracheal samples were taken from chickens in 30 closelymonitored broiler flocks suffering from respiratory disease with a mortality rate above theusual range. RT(Reverse Transcriptase)-PCR was performed in order to detect the M proteinand the H9 gene of avian influenza A. The multiplex nested RT-PCR was also performed todetect Massachusetts, 793B (4/91) and D274 serotypes of IBV in the samples. In this study,AIV and IBV were detected in 16 (53/3%) and 12 (40%) out of 30 flocks, respectively. Thetracheal samples of 11 out of 12 flocks were positive for 4/91 strain of IBV and one forMassachusetts serotype. A mixed infection of AIV (H9 subtype) and IBV (4/91 serotype) wasobserved in four flocks with severe lesions and 20-30% mortality. The results of this studyindicate the high occurrence of natural co-infection of AIV and IBV in Iranian broiler chickenfarms showing respiratory signs and they show that mortality rate in co-infected flocks weresignificantly (p<0.05).higher than other flocks sampled.