Ornithobacterium rhinotracheale in Moroccan Poultry: Antimicrobial Susceptibility Profiles, Characterization of Recent Isolates, and Retrospective Study (2019–23) of Its Occurrence in Different Poultry Production Systems

<i>Ornithobacterium rhinotracheale</i> (ORT) is one of the most important respiratory pathogens of poultry, notably in turkeys, while <i>Riemerella anatipestifer</i> (RA) is the etiologic agent of infectious serositis, the most economically significant disease of domestic ducks and, to a lesser extent, geese and turkeys. Currently, little is known about ORT and RA infections in Moroccan poultry. Thus, the main aim of this study was to describe ORT incidence in Moroccan poultry flocks during the period from 2019 to 2023 and gain better insights into genetic characteristics in combination with assessment of antimicrobial susceptibility of Moroccan ORT isolates during 2023 outbreaks. In addition, we report the first detection of RA in Moroccan turkeys and caged layer chickens. For this purpose, poultry flocks exhibiting elevated mortality rates along with respiratory clinical signs were necropsied. Additionally, the birds presenting fibrinous pleuropneumonia were investigated for ORT infection during the period from January to December 2023. Samples of the lungs, air sacs, and tracheas were collected for bacteriology testing, and the antimicrobial susceptibility testing was conducted on the isolates. Furthermore, trachea and lung samples were subjected to real-time quantitative polymerase chain reaction (qPCR), and positive qPCR samples were then selected for further amplification of the <i>rpoB</i> gene, followed by sequencing. Moreover, a retrospective study of the incidence of ORT from 2019 to 2023 was carried out. The results showed a significant increase of ORT cases (<i>p</i> , 0.001); additionally, age was identified as the sole significant risk factor associated with ORT diagnosis in the multivariable logistic regression analysis (odds ratio = 4.87, 95% confidence interval = 2.54-9.37, <i>p</i> , 0.001). Bacteriology confirmed 10 ORT isolates. Additionally, antimicrobial susceptibility testing revealed complete resistance to several antibiotics, with varying levels of resistance and sensitivity across isolates, including 100% sensitivity to florfenicol in broilers and turkeys. Sequencing of the <i>rpoB</i> gene revealed that 10 ORT isolates had nucleotide similarity ranging from 98% to 100% with other known ORT isolates from chickens and turkeys reported in the U.K., Chile, China, Portugal, and the United States. On the other hand, two ORT isolates were found to be genetically very close to known RA strains, despite testing positive for ORT by real-time qPCR. Amino acid sequence comparisons for these isolates reached 83.10% similarity with <i>Riemerella</i> sp. strain WJ4 isolated in China and 98.79% similarity with strain IPDH 98/90 isolated in Germany. In conclusion, the prevalence of ORT in Moroccan poultry flocks increased over the 5-yr period covered by this retrospective study, contributing significantly to recent respiratory disease outbreaks. Additionally, RA may also contribute to polyserositis in poultry; however, further studies are needed to determine its pathogenicity.