Molecular detection of Rickettsia helvetica in lesion and blood samples after tick bites in Serbia: two cases with One Health implications

Rickettsia helvetica is a spotted fever group rickettsia associated mainly with Ixodes ricinus and increasingly detected in European ticks. We describe two tick-bite-associated human cases in Serbia in May 2025. A 65-year-old woman (Case 1) developed pruritic erythematous lesions after two adult female I. ricinus attachments acquired in the Valjevo area. Rickettsia spp. DNA was detected in capillary blood from both lesions, and sequencing of the PCR amplicons identified R. helvetica, while whole blood was PCR-negative and serology did not show reproducible seroconversion. An 8-year-old girl (Case 2) developed a pruritic scalp papule/crust and occipital/cervical lymphadenopathy after an adult female Haemaphysalis punctata attachment in Petrovaradin forest. Rickettsia spp. DNA was detected in lesion capillary blood and whole blood; sequencing identified both as R. helvetica. Clinical signs resolved after doxycycline. These observations support lesion-focused molecular testing and integrated human-tick-environment surveillance for underdiagnosed spotted fever group rickettsioses in Serbia.