Tick-borne pathogens in a nature reserve area in the Netherlands: serological and molecular assessments in large herbivores and Ixodes ricinus ticks.

Ticks are vectors of a wide range of pathogens, relevant to both veterinary and public health. Although tick surveillance is frequently conducted in the Netherlands, data on tick-borne pathogens in free-living herbivores remains limited, leaving the impact of these pathogens on animal health poorly understood. This study aimed to characterise tick species and determine seroprevalence and infection prevalence of selected tick-borne pathogens in large herbivores at the Oostvaardersplassen nature reserve and questing ticks collected in the area. Between September 2023 and December 2024, blood was opportunistically sampled from Heck cattle, Konik horses, and red deer culled for population control, and questing ticks were collected. Serum, blood, and pooled tick samples were tested for tick-borne encephalitis virus (TBEV), Anaplasma spp., A. phagocytophilum, Babesia spp., B. microti, B. caballi and Theileria equi, Borrelia burgdorferi s.l., and B. miyamotoi using serological and molecular methods. In total, 2617 questing Ixodes ricinus were collected. In red deer (n = 177), seropositivity was 6.2% for TBEV, prevalence was 58.9% for A. phagocytophilum, and 53.4% for Babesia spp. (predominantly B. divergens and B. cf. odocoilei). Corresponding values in cattle (n = 36) were 0%, 14.3%, and 3.6%, and in horses (n = 89) 0%, 1.2%, and 0%, respectively. In questing ticks, TBEV (0.04%), Babesia spp. (1.5%; mainly B. venatorum and B. cf. odocoilei; excluding B. microti), B. microti (1.9%), B. burgdorferi s.l. (8.5%), B. miyamotoi (1.8%), and A. phagocytophilum (1.1%) were detected. This study provides new evidence of TBEV circulation and confirms active transmission of multiple tick-borne pathogens at Oostvaardersplassen. These findings support integrating systematic tick surveillance into existing monitoring programmes at nature reserves, strengthening One Health informed disease surveillance to safeguard animal and public health.