Genomic detection of Coxiella burnetii based on plasmid genes in horses

Q fever is a worldwide zoonosis caused by an obligate intra-cellular pathogen called Coxiella burnetii affecting a broad range of animal hosts including horses. Most of the isolates found carry plasmids which genetic studies of C. burnetii strains suggest a critical role in C. burnetii survival. The correlation between an isolated plasmid type and the chronic or acute nature of the disease has always been controversial. This study was conducted to investigate the prevalence of C. burnetii QpH1 and QpDG plasmids in horses and assess the potential role of these species as reservoirs of infection and transmission. Nested-polymerase chain reaction (PCR) assays were performed on 320 blood serum samples drawn from horses in West Azerbaijan province, Iran, in 2020. In total, 26 (8.13%) Q fever-positive samples based on containing the IS1111 gene were tested by nested-PCR approach to amplify QpH1 and QpDG plasmid segments. The QpH1 and QpRS plasmid-specific sequences were identified in 19 (73.07%) and none in the serum samples, respectively. According to the present study, the age of the animal can be considered as an important risk factor for the prevalence of C. burnetii; but, the season, sex, and breed of the horse had no effect on the prevalence of disease. The results indicate that nested-PCR method could be suitable for routine diagnosis, to gather new information about the shedding of C. burnetii, and to improve the knowledge of contamination routes.