Red foxes (Vulpes vulpes) are a natural intermediate host of Neospora caninum

The present study was undertaken to determine if red foxes are natural intermediate and/or definitive host for Neospora caninum and to study the importance of infection of N. caninum in this species in North-eastern Spain. Faecal samples and brain tissues were obtained from 122 foxes from 21 rural areas of Catalonia. Faeces collected were examined for parasite eggs and coccidian oocysts using sucrose flotation. For PCR-based diagnosis of N. caninum in brain tissues, the specific genomic Nc5 region was selected as the target sequence for DNA amplification. To control for PCR failure and facilitate identification of truly negative samples, the competitor pNc5C molecule was added to all negative samples in a second round of PCR reactions. Of the 122 foxes analysed, 13 (10.7%) were positive by PCR for N. caninum. Signal intensities of all positive samples were relatively weak with the exception of one sample from a 3-month male animal, that also showed the highest repeatability. No differences were observed by sex, age or area of sampling analysis. Detection of stages of N. caninum in brain from naturally infected red foxes demonstrated that red foxes are a natural intermediate host for N. caninum. Faecal samples were analysed for the presence of N. caninum oocysts, however, no oocysts compatible with N. caninum were found. A widespread latent infection of red foxes in North-eastern Spain found in the present study indicates that red foxes could have a very important role in the epidemiology of neosporosis in our area.