Abstract: Background Tick-borne diseases (TBDs) causing anemia and systemic illness in dogs are increasing worldwide due to climate change and shifting vector populations. Given their zoonotic potential and One Health relevance, regional data are crucial; however, large-scale molecular studies in South Korea remain limited. Hypothesis/Objectives To characterize the prevalence, infection patterns, and seasonal distribution of major tick-borne pathogens in dogs with suspected TBD or anemia using molecular diagnostics. Animals Blood samples (n = 15,592) from dogs with suspected TBD or anemia. Methods Real-time polymerase chain reaction data from samples submitted by 1,072 veterinary hospitals to a commercial veterinary laboratory (April 2016–July 2024) were retrospectively analyzed. Results Pathogens were detected in 3,446/15,592 samples (22.1%). Single infections predominated (98.9%), while co-infections (0.29%) and mixed infections (0.78%) were rare. Among single infections, Babesia spp. were most prevalent (93.6%), followed by Anaplasma spp. (1.9%) and hemotropic Mycoplasma spp. (1.8%). The most common co-infection was Babesia spp. with Hepatozoon spp. (0.26%), and the most frequent mixed infection involved Babesia spp. with hemotropic Mycoplasma spp. (0.55%). Severe fever with thrombocytopenia syndrome virus (SFTSV) was detected in 45 cases. Most positive cases occurred in autumn (60.0%). Conclusions and Clinical Importance This large-scale study identifies Babesia spp. as the primary TBD pathogens in South Korean dogs, showing significant seasonal variation. These findings enable clinicians to better predict causative agents in dogs with anemia or TBD signs, facilitating prompt decisions. The results underscore the clinical utility of molecular diagnostics and the need for seasonally informed strategies in endemic regions.
