Dogs shed Neospora caninum oocysts after ingestion of naturally infected bovine placenta but not after ingestion of colostrum spiked with Neospora caninum tachyzoites

An experiment was carried out to determine whether bovine colostrum or plac enta could be a source of infection of Neospora caninum for dogs. For this purpose, two dogs were fed bovine colostrum to which culture-derived N. can inum tachyzoites were added and two other dogs were fed placental cotyledon ary tissue from N. caninum seropositive cows. One dog served as a negative control during the start of the experiment but this control dog was fed cot yledonary tissue later on. None of the dogs did produce serum antibodies to N. caninum. All three dogs that were fed cotyledonary tissue did shed N. c aninum oocysts, bur no oocyst shedding was seen in the two dogs that were f ed colostrum with N. caninum,l tachyzoites. Oocyst excretion did not resume in two dogs after repeated feeding of N. caninum infected placenta. The id entity of the oocysts: was confirmed by a bioassay in gerbils. It is conclu ded that ingestion of bovine placenta by dogs is an effective mode of trans mission of N. caninum from cattle to dogs. (C) 2001 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.