Molecular detection by PCR of Rickettsia rickettsii in canines in Ciudad Obregón, Sonora, México

Abstract

Introduction: Rickettsia is an intracellular, Gram-negative, zoonotic bacterium that is transmitted by arthropods, such as ticks, fleas and lice. Rickettsioses have been reported in Mexico since the 1930s, with a higher prevalence in the northern states. Infections affect both dogs and humans in marginalized areas, with Rickettsia rickettsii being the most pathogenic species and associated with high mortality rates.

Methodology: This study aimed to detect R. rickettsii in dogs from Ciudad Obregón, Sonora, using the ompA gene PCR. Between July and August 2024, 110 EDTA whole blood samples were collected: 95 from dogs with a presumptive clinical diagnosis of rickettsiosis, and 15 from stray dogs with active tick infestations. DNA extraction, PCR amplification and product purification were performed at the Veterinary Molecular Biology Laboratory of the Instituto Tecnológico de Sonora. Sanger sequencing, Snap Gene Viewer, and BLASTn against GenBank were used to confirm the identity of the sequences.

Results: Sequencing of the ompA fragment confirmed 99–100% homology with R. rickettsii. One positive case (6.7%) was detected, corresponding to a stray dog from a disadvantaged area of the municipality of Cajeme, indicating the presence of the pathogen in a localized area.

Conclusions: The detection of R. rickettsii in a stray dog in Ciudad Obregón confirms the presence of the pathogen in the area, highlighting the importance of free-roaming canines and environmental conditions in sustaining vectors. Early diagnosis and control of ectoparasites are critical to reducing zoonotic transmission, underlining the importance of continuous molecular surveillance in public health.