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

In a previous paper we demonstrated that Hammondia heydorni-like oocysts isolated in 1996 from a naturally infected dog could not be distinguished from 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 used for the cyclical transmission of this isolate. The majority of dogs that had shed oocysts showed no sero-conversion with respect to N. caninum tachyzoite surface or immunodominant antigens, either in the indirect fluorescent antibody test or in two Western-blot-based tests. In addition to the examination of responses to immunodominant antigens, we also analysed the antibody reactions of dogs to a high-molecular-weight antigen (152 kDa) in the tachyzoite antigen preparation. The antibodies against this antigen appeared 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 initial information on a 152 kDa tachyzoite antigen, which might be a suitable candidate to identify dogs with a history of shedding N. caninum oocysts.