Canine distemper virus in sympatric carnivores of eastern Spain: A potential risk for reintroduction programs

Canine distemper virus (CDV) is a highly infectious morbillivirus posing a significant threat to global carnivore biodiversity. While domestic dogs are primary reservoirs, CDV circulates among various free-ranging wildlife populations, suggesting complex maintenance mechanisms. We assessed CDV frequency of infection via RT-qPCR and serology in 106 free-ranging wild carnivores (families Canidae, Mustelidae, and Viverridae) collected opportunistically in the Valencian Community, Spain, between 2022 and 2025. A total of 212 tissue samples-comprising adult lung (n = 102) and brain (n = 104) tissues, along with samples from two fetuses (n = 6), were screened for viral RNA, and 84 individuals were tested for antibodies. The overall molecular frequency of infection was 11.3% (n = 12), with most positives identified in red foxes (Vulpes vulpes). The reported Ct values (10.16-34.79) reflected a broad spectrum of viral loads; specifically, the low mean value (22.76) and high-load cases (Ct < 20) suggested active or recent infections, while higher Ct values indicated late-stage or subclinical cases. Seropositivity was observed in 9.5% (8/84) of the animals. Notably, viral RNA was detected in the brain of a pregnant common genet (Genetta genetta), though fetuses and placental tissues remained negative. These findings confirm ongoing CDV circulation in eastern Spain and underscore the necessity of long-term surveillance in regions considered for future conservation initiatives, such as the reintroduction of the endangered Iberian lynx (Lynx pardinus).