Molecular detection of shared pathogens in red foxes (Vulpes vulpes) from farming habitats in northwestern Spain

Wildlife species are increasingly inhabiting fragmented and human-modified landscapes, leading to more frequent contacts at the wildlife-livestock-human interface and creating opportunities for the circulation of shared pathogens with important implications for animal and public health, as well as for biodiversity conservation. Understanding pathogen dynamics in wildlife is therefore essential for integrated sanitary surveillance and risk assessment. In this study the occurrence of four shared pathogens - canine distemper virus (CDV), canine adenovirus type 1 (CAdV-1), Toxoplasma gondii and Neospora caninum - in red fox (Vulpes vulpes) inhabiting northwestern Spain was investigated to assess its potential role in pathogen circulation across the wildlife-livestock interface and identify factors associated with infection, i.e., the relationship between pathogen positivity and pathogen richness, individual traits (sex and age), and habitat type (farming or forest). The brains of 239 legally hunted red foxes were analysed by polymerase chain reaction (PCR). The highest prevalence was observed for CDV (7.53%; 95% CI: 4.5%-11.6%; 18/239), followed by T. gondii (7.11%; 95% CI: 4.19%-11.14%; 17/239) and N. caninum (4.60%; 95% CI: 2.31%-8.08%; 11/239), whereas only 1.67% (95% CI: 0.45%-4.22%; 4/239) of foxes tested positive for CAdV-1. CDV and T. gondii were significantly associated with farming habitats, highlighting the importance of red foxes in pathogen circulation where wildlife, livestock and humans coexist. These findings support the use of red fox as sentinel species for integrated sanitary surveillance and contribute to understanding pathogen transmission risks across human-modified landscapes.