Serological evidence for naturally occurring transmission of Neospora caninum among foxes (Vulpes vulpes).

The study describes the time course of the Neospora caninum-specific antibody response in experimentally infected foxes, in naturally N. caninum-seropositive vixens and their litters. An immunofluorescence test, a tachyzoite surface antigen based ELISA and an immunoblot assay were established for this purpose. The immunoblot patterns of naturally seropositive and experimentally infected foxes revealed a high degree of similarity and resembled those reported for other intermediate host species. Reactions against immunodominant antigens of Mr 56, 68 and >94 kDa were observed which could be linked with a period of 14 days-2 months post experimental infection with tachyzoites. Cubs born by naturally seropositive vixens were found to be persistently or transiently seropositive, in the latter case, specific antibodies were detected only up to 44 days after birth. These antibodies may thus be of maternal origin. Differences between the immunoblot patterns of persistently positive cubs, those of their mothers and of transiently positive cubs, in particular the differential response to antigens of Mr 56 and 68 kDa, prove that cubs with persistent antibodies had actively mounted an antibody response. This result provides the first evidence for the postnatal or vertical transmission of N. caninum among naturally seropositive foxes.