Abstract
Newcastle disease virus (NDV), Infectious bronchitis virus (IBV) and H9N2 avian influenza virus (AIV) are the most significant respiratory pathogens. Several outbreaks have been reported frequently in Saudi Arabia despite of the intensive use of vaccination programs. Ten broiler flocks suffering from complicated respiratory disease were subjected to necropsy and samples were collected for molecular identification of involved viruses and pathogenic bacterial infections. Seven out of the ten flocks were positive for single or combined viral infection. The seven flocks were positive for HA test. All positive samples were subjected for molecular identification, three flocks were positive for single NDV while one flock was positive for both NDV and IBV. Three flocks were positive for H9N2 and IBV. Three flocks were negative for viral infection and subjected for pathogenic bacteria detection. The sequence analysis of F gene of NDV revealed that all isolates exhibited the cleavage site ((112)RRQKRE(117)) of virulent NDVs. The neuraminidase-haemagglutinin gene revealed that all AI isolates belonged to H9N2 low pathogenic avian influenza virus (LPAIV) subtype. The S1 gene of IBV showed that one isolate was closely related to the Connecticut IBV strain while another isolate belonged to the H120 IBV strain. In conclusion, combined pathogens causing respiratory infection in broilers is very common, which leads to the increase in disease severity and economic losses. The continuous detection of virulent NDV as well as IBV from broiler flocks emphasize the need to review the vaccination strategies based on further epidemiological and molecular studies.