Pathogenic bacteria associated with outbreaks of respiratory disease in Iranian broiler farms.

Background: Multi-causal respiratory infections are more commonly observed than uncomplicated cases with single agents in the commercial poultry industry. Recently, increased mortality rates associated with respiratory clinical signs have been reported in Iranian broiler farms.
Objectives: The present study aimed to determine the spectra of avian mycoplasmas (Mycoplasma gallisepticum, MG and Mycoplasma synoviae, MS) and Ornithobacterium rhinotracheale (ORT) in the broiler farms with the multi-causal respiratory disease (MCRD) from 2017 to 2020.
Methods: Trachea and lung tissue samples were collected from 70 broiler flocks presenting increased mortality and acute respiratory disease. MG, MS, and ORT were detected by performing polymerase chain reaction with primers complementary to the 16S rRNA, vlhA, and 16S rRNA genes, respectively.
Results: Genetic materials of MG, MS, and ORT were detected in five, three, and five of the 70 flocks. Based on the phylogenetic analysis of the complete mgc2 coding sequences, all MG strains formed a distinct cluster along with other Iranian MG isolates. According to the phylogenetic analysis of the partial vlhA gene of MS strains, two isolates were located along with Australian and European strains. In addition, one of them displayed an out-group association with MS isolates from Jordan. Phylogenetic analysis of Iranian ORT strains using a partial sequence of the 16S rRNA gene showed a distinct group among the other ORT strains.
Conclusions: The results indicate that MG, MS, and ORT are not predominantly responsible for the MCRD. However, continuous monitoring of poultry flocks could be significant for obtaining valuable information related to different MG, MS, and ORT strains and designing effective control strategies.
(© 2023 The Authors. Veterinary Medicine and Science published by John Wiley & Sons Ltd.)