A quantitative analysis of tick-borne pathogens carried by questing Ixodes persulcatus in northern Sweden

Sammanfattning

Background Ticks serve as vectors for many pathogens, many of which are zoonotic and can cause clinical symptoms in both animals and humans. In Sweden the most common vector of tick-borne pathogens (TBP) is the tick species Ixodes ricinus. Recently the tick species Ixodes persulcatus has established permanent populations in Sweden’s northern territories which were previously naïve to the species. This tick species can carry an array of pathogens like those carried by the sheep tick I. ricinus. The study aimed at analysing the prevalence of two TBPs: Anaplasma phagocytophilum and Babesia spp. in questing I. persulcatus collected in Norrbotten county in Sweden. A. phagocytophilum is an intracellular bacterium that infects host neutrophils, and Babesia spp. is an intracellular parasite that instead infects erythrocytes. These pathogens some cause concern regarding public health but are mainly a problem for animal health and welfare, and the profitability of the farming sector. Method The ticks were sampled via cloth dragging in Norrbotten county in May 2025 and were subsequently identified to species level. In total 533 questing I. persulcatus ticks were collected and analysed. TaqMan Real-time PCR was subsequently employed to quantitatively analyse nucleic acid samples of the ticks to detect the pathogens. Results and discussion Results showed that no ticks were positive for either of the pathogens. A low prevalence of A. phagocytophilum and Babesia spp. in I. persulcatus is supported by previous research conducted on ticks in northern Scandinavia. However, the same tick species is known to carry these pathogens in higher prevalences elsewhere. A possible explanation of the low prevalence of these pathogens in northern Scandinavia is due to a complex web of factors that determine the spread of a TBP and is not limited to just host-availability. I conclude that it is important to keep monitoring the prevalence of TBPs and to screen for more pathogens to better understand the risk they pose. Additionally, I propose that future research aims at analysing the seroprevalence and active infections of hosts and reservoir hosts in the region to understand the potential threat I. persulcatus poses in northern Sweden and to better understand how TBPs spread globally.