Cyclic transmission of Neospora caninum: serological findings in dogs shedding oocysts

In a previous paper we demonstrated that Hammondia heydorni-like oocysts is olated in 1996 from a naturally infected dog could not be distinguished fro m the isolate Neospora caninum NC-1. The isolate, designated as H. heydorni -Berlin-1996, was cyclically transmitted using dogs as the final hosts. The present study provides information on the antibody responses of the dogs u sed for the cyclical transmission of this isolate. The majority of dogs tha t had shed oocysts showed no sero-conversion with respect to N. caninum tac hyzoite surface or immunodominant antigens, either in the indirect fluoresc ent antibody test or in two Western-blot-based tests. In addition to the ex amination of responses to immunodominant antigens, we also analysed the ant ibody reactions of dogs to a high-molecular-weight antigen (152 kDa) in the tachyzoite antigen preparation. The antibodies against this antigen appear ed after the dogs had been fed infected intermediate host tissues and shed oocysts. The reaction was observed in dogs between day 35 and day 447 after feeding of intermediate host tissues. Therefore, our study provides initia l information on a 152 kDa tachyzoite antigen, which might be a suitable ca ndidate to identify dogs with a history of shedding N. caninum oocysts.