Tick-borne pathogens in Swedish wild boar and their attached ticks: the first detection of Borrelia species in wild boar in northern Europe

Background The wild boar ( Sus scrofa ) population has expanded in northern Europe, yet their role in the ecology of tick-borne pathogens remains poorly understood. This study investigated the occurrence of Anaplasma phagocytophilum and Borrelia burgdorferi sensu lato in 88 Swedish wild boar and their attached Ixodes ricinus ticks by analysing multiple tissues (spleen, heart, urinary bladder and skin) using quantitative PCR. Results Anaplasma phagocytophilum was detected in 20 (22.7%) wild boar, with infections (i.e. quantitative PCR positive) more common in juveniles than adults. Infection probability was lowest in spring but markedly higher in summer and autumn. Borrelia species DNA was detected in three juvenile males (3.4%), representing the first report of Borrelia species in wild boar in northern Europe. Thirty attached ticks were collected from 17 wild boar. Six ticks carried A. phagocytophilum , five carried Borrelia species, and one was coinfected. Ticks were more likely to be infected when collected from infected wild boar than from uninfected hosts, while feeding duration showed no detectable association with infection in either hosts or ticks. Conclusions These findings provide new insight into the occurrence of tick-borne pathogens in wild boar and highlight the value of multi-tissue sampling and paired host–tick data for understanding pathogen dynamics in wildlife populations.