Evidence for the long-distance transport of ticks and tick-borne pathogens by human travellers to Texas, USA

Abstract

Background: The incidence of tick-borne diseases in the USA has surged in recent years, with >50 000 cases reported from an estimated half-million cases annually. While domestic vectors are well characterized, the role of human travel in transporting exotic ticks and pathogens remains poorly understood.

Methods: We analysed 4808 submissions of ticks removed from individuals to the Tick-Borne Disease Research Laboratory in Texas, USA, from 2004 to 2024. Tick species were identified phenotypically or through DNA-based sequencing, and pathogens (Borrelia spp., Rickettsia spp., Ehrlichia spp., Anaplasma phagocytophilum and Babesia microti) were detected using molecular assays. Submitter travel histories were cross-referenced with known tick geographic ranges to identify long-distance transport.

Results: We documented cases of intercontinental, international and domestic interstate transport of ticks by human travellers. Four Ixodes ricinus ticks-originating from Europe-were transported to Texas; one tick carried Borrelia afzelii, a Lyme disease pathogen not endemic to North America. Central and South American Amblyomma species were repeatedly imported, raising concerns for pathogen transmission and tick establishment. Domestic travellers also carried Ixodes scapularis ticks infected with Borrelia burgdorferi sensu stricto, Babesia microti and A. phagocytophilum from Lyme-endemic regions of the USA to Texas, along with non-native species Ixodes pacificus, Dermacentor andersoni and Dermacentor occidentalis from endemic areas in the western United States.

Conclusions: Long-distance transport of ticks by travellers represents an underrecognized pathway for the global spread of ticks and tick-borne pathogens. Clinicians should consider travel history in tick-borne illness diagnostics. Enhanced surveillance, public education and travel screening are critical to mitigating these risks.

Keywords: Amblyomma; Borrelia afzelii; Ixodes; Ixodes ricinus; Tick-borne diseases; emerging pathogens; international travel; vector-borne infections.