In contrast to dogs, red foxes ( Vulpes vulpes) did not shed Neospora caninum upon feeding of intermediate host tissues

To clarify whether red foxes (Vulpes vulpes) can be final hosts of Neospora caninum, foxes and dogs were fed in parallel on tissues of a sheep and a goat experimentally infected with N. caninum. The faeces of at least two of five dogs contained N. caninum oocysts, as determined by bioassay. In the faeces of all six foxes fed in parallel, oocysts were detected that were larger in size (length 12.6+/-0.5 mum, width 11.8+/-0.4 mum) than the oocysts shed by the dogs. Ribosomal RNA sequences and the results of an immunoblot-based bioassay provided further evidence that these oocysts were different from N. caninum. A titration experiment performed to determine the sensitivity of a bioassay utilising gerbils showed that as few as five sporulated N. caninum oocysts could be detected by this test. This indicates that, in two feeding experiments, less than 3,700 and 200 sporulated N. caninum oocysts. respectively, could have been among the Hammondia sp.-like oocysts collected from fox faeces. These results suggest that the red fox is either an inappropriate final host for N. caninum or not at all a final host for this parasite