Analysis of ticks (Acari: Ixodida) and associated microorganisms collected on the North Sea Island of Heligoland.

Heligoland is an island located in the North Sea, where vegetation was almost destroyed as a result of heavy bombardment during and after the Second World War. However, over the past 70 years, the vegetation has developed from scrub towards bushy or even forested environments. This change has most likely altered habitat suitability for various organisms, including many species of ticks. Ticks can act as major vectors for various pathogens of humans and animals; thus, characterizing the occurrence of a tick population and associated microorganism on the island is of great importance in relation to public and animal health. For this characterization on Heligoland, we flagged ticks at four different locations during June 2023 and 2024. In 2024, ticks were opportunistically sampled from house pets living on the island and during the annual ringing of common murre (Uria aalge) fledglings. In total, 267 ticks were collected over the 2 years which were identified morphologically, and confirmed molecularly if needed, to four species: Ixodes ricinus (n = 132), Haemaphysalis punctata (n = 47), Ixodes uriae (n = 3), and Alectorobius maritimus (n = 85), which for the latter represents the first report in Germany. Questing tick samples positive for Borrelia burgdorferi sensu lato, Rickettsia spp., Anaplasma phagocytophilum, and Babesia spp. were found in one or both years. Subsequent sequencing showed the presence of two Rickettsia species (R. helvetica, R. aeschlimannii), multiple Borrelia species (B. garinii, B. valaisiana, B. bavariensis, B. afzelii), and two Babesia species (Ba. venatorum, Ba. capreoli). Our research highlights a diverse tick and associated microorganism population on the island, which could pose public and animal health risks that will need to be monitored in the future.