Subcutaneous Ticks in Wild Carnivores: Any Host-Related Differences?

Simple Summary Ticks are obligate parasites living part of their life attached on the skin surface of different mammal species. In the last decades, there have been several reports of ticks found dead underneath the skin of foxes, raccoon dogs, golden jackals, domestic dogs, and a human being. The biological reasons behind this phenomenon are still unclear, although most of the reports are in canid species, suggesting that the immunological response of canids might favor it. The aim of this study was to investigate the presence of ticks under the skin of different wild carnivore species in Northwestern Italy, where they have never been described before. Out of 63 wild carnivores, 11 foxes were found infested with 51 dead ticks under the skin of the animals. All the preserved ticks collected underneath the skin of the foxes were identified as Ixodes spp., meaning that this tick species might be more frequently involved in the phenomenon, as already suggested by the scientific community. By contrast, no subcutaneous ticks were found in wolves, the other most prevalent wild canid species in Northwestern Italy, supporting the idea that the immune reaction of wolves may not favor the embedment of ticks underneath the skin. Ticks under the skin have been shown in different canid species such as red fox, domestic dog, and raccoon dog. Despite being increasingly reported in Europe in the last decade, the biological mechanisms associated to subcutaneous ticks (SCT), as well as the predisposing factors, are not yet clear. The main goal of this study was to investigate the presence of SCT in wild carnivores in Northwestern Italy. Sixty-three wild carnivores were examined, and SCT were submitted to histological examination or stored in ethanol for morphological and molecular identification. A portion of the cox1 gene and 16S rDNA were amplified, and positive PCR products were sequenced. Fifty-one small brown-coloured nodules of about 2 x 3 mm containing ticks in different decomposition stages were observed in 11 out of 30 foxes. Seven ticks were classified as Ixodes ricinus, while 14 ticks were determined only at the genus level (Ixodes spp.), and in two ticks no morphological key was applicable due to the advanced degradation status. By PCR, the rDNA fragment of six ticks (26.1%, 95% CI: 12.6-46.5%) was amplified, and BLAST analysis revealed a 99-100% nucleotide similarity to I. ricinus. At the histological examination, the inflammatory response varied from a mild to a moderate mixed infiltrate, primarily composed by neutrophils and lymphocytes. The results of this study confirm foxes as the main wild reservoir for SCT. The absence of SCT in other carnivores (badgers and martens) is in accordance with other studies. Ixodes ricinus is the most frequently reported tick species, corroborating the idea that longirostral ticks might be more frequently associated to SC embedment than brevirostral ticks.