Thelazia callipaeda infection in Northwestern Spain: what role does the Iberian wolf play?

<i>Thelazia callipaeda</i> is a vector-borne parasite infecting the eyes of domestic and wild animals, as well as humans, across Europe. In Spain, it is endemic in several regions, with high prevalence reported in dogs and cats, but data on wildlife remain scarce. This study investigated the prevalence of <i>T. callipaeda</i> in Iberian wolves (<i>Canis lupus signatus</i>) from northwestern Spain and explored epidemiological factors associated with infection. Between 2016 and 2025, 182 wolves from Asturias and Galicia (A Coruña, Lugo, Ourense and Pontevedra) were sampled after necropsy. Eyeworms were collected and identified using morphological and molecular methods, with all specimens corresponding to <i>T. callipaeda</i> genotype h1. The overall prevalence was 17 %, with higher rates of infection in Galicia (18.2 %) than Asturias (8.7 %). Infections were restricted to Ourense (37.2 %) and Lugo (26.5 %). Parasite burdens were higher in females and immature wolves (1-3 years) compared to older animals and those in good body condition (BC 4-5). The distribution of infected wolves was associated with the vegetation around Miño and Sil river basins, which may favor the development of the vector <i>Phortica variegata</i>. Lower prevalence in pups could be linked to smaller eye size and lower body condition, while sex- and age-related differences may reflect behavioral or immunological factors. These results indicate that Iberian wolves can act as reservoirs of <i>T. callipaeda</i> in northwestern Spain, underscoring the need for further research into their role in the epidemiology of this zoonotic parasite.