Geographical distribution of <i>Hyalomma marginatum</i> Koch, 1844 in northwestern Spain from 2019 to 2024: A one health approach

Hyalomma marginatum Koch, 1844, is a competent vector of the Crimean-Congo hemorrhagic fever virus (CCHFV) and other zoonotic pathogens, typically associated with warmer Mediterranean environments. Between 2019 and 2024, as part of the activities of the Galician Vector Surveillance Network (ReGaViVec), a passive surveillance program was carried out in the northwest of the Iberian Peninsula, involving regional Healthcare centers, livestock farms, equestrian facilities, Wildlife Rescue Centers, Veterinary clinics and private individuals. A total of 63 adult specimens were morphologically identified as H. marginatum, collected from humans (60.3%), free-range ungulates (35%), dogs (3.2%) and the environment (1.6%). The annual distribution ranged from 1.6% of the total in 2019 to 57.1% in 2024. Seasonal activity peaked in spring (54%), declined slightly in summer (44%) and was absent in winter. Most specimens (82.5%) came from areas under a Mediterranean climate and warm summers, and 66% were collected at locations less than 15 km from where the first specimen was found. Human infestations were primarily associated with agricultural activities (47.6%) and recreational walking in wooded areas (42.9%). Regarding human anatomical distribution, the most frequent attachment sites were the trunk (34.2%) and the lower extremities (21.1%). The continuing detection of H. marginatum ticks in the study area, along with changes in their spatial distribution over a 6-year period, highlights the need to implement surveillance protocols based on a 'One Health' approach to monitor the potential establishment of this vector in NW Spain, as well as the risk of some pathogens associated with it.