Background: South Downs National Park (SDNP) is UK's most visited National Park, and a focus of tick-borne Lyme disease. The first presumed UK autochthonous cases of tick-borne encephalitis and babesiosis were recorded in 2019-20. SDNP aims to conserve wildlife and encourage recreation, so interventions are needed that reduce hazard without negatively affecting ecosystem health. To be successful these require knowledge of site hazards.

Methods: British Deer Society members submitted ticks removed from deer. Key potential intervention sites were selected and six 50 m² transects drag-sampled per site (mostly twice yearly for 2 years). Ticks were identified in-lab (sex, life stage, species), hazard measured as tick presence, density of ticks (all life stages, DOT), and density of nymphs (DON). Sites and habitat types were analysed for association with hazard. Distribution was mapped by combining our results with records from five other sources.

Results: A total of 87Ixodes ricinus (all but one adults, 82% F) were removed from 14 deer (10Dama dama; threeCapreolus capreolus; one not recorded; tick burden, 1-35) at 12 locations (commonly woodland). Five key potential intervention sites were identified and drag-sampled 2015-16, collecting 623 ticks (238 on-transects): 53.8% nymphs, 42.5% larvae, 3.7% adults (13 M, 10 F). Ticks were present on-transects at all sites:I. ricinus at three (The Mens (TM); Queen Elizabeth Country Park (QECP); Cowdray Estate (CE)),Haemaphysalis punctata at two (Seven Sisters Country Park (SSCP); Ditchling Beacon Nature Reserve (DBNR)). TM had the highest DOT at 30/300 m² (DON = 30/300 m²), followed by QECP 22/300 m² (12/300 m²), CE 8/300 m² (6/300 m²), and SSCP 1/300 m² (1/300 m²). ForI. ricinus, nymphs predominated in spring, larvae in the second half of summer and early autumn. The overall ranking of site hazard held for DON and DOT from both seasonal sampling periods. DBNR was sampled 2016 only (one adultH. punctata collected). Woodland had significantly greater hazard than downland, but ticks were present at all downland sites.I. ricinus has been identified in 33/37 of SDNPs 10 km² grid squares,Ixodes hexagonus 10/37,H. punctata 7/37,Dermacentor reticulatus 1/37.

Conclusions: Mapping shows tick hazard broadly distributed across SDNP.I. ricinus was most common, butH. punctata's seeming range expansion is concerning. Recommendations: management of small heavily visited high hazard plots (QECP); post-visit precaution signage (all sites); repellent impregnated clothing for deerstalkers; flock trials to controlH. punctata (SSCP, DBNR). Further research at TM may contribute to knowledge on ecological dynamics underlying infection density and predator re-introduction/protection as public health interventions. Ecological research onH. punctata would aid control. SDNP Authority is ideally placed to link and champion policies to reduce hazard, whilst avoiding or reducing conflict between public health and ecosystem health.

The authors declare that they have no competing interests.