First isolation of Neospora caninum from the feces of a naturally infecteddog

Neospora caninum is a major cause of abortion in cattle worldwide. Cattle b ecome infected with N, caninum by ingesting oocysts from the environment or transplacentally from dam to fetus. Experimentally, dogs can act as defini tive hosts, but dogs excrete few oocysts after ingesting tissue cysts. A na tural definitive host was unknown until now. In the present study, N. canin um was isolated from the feces of a dog. Gerbils (Meriones unguiculatus) fe d feces from the dog developed antibodies to N. caninum in the Neospora can inum agglutination test, and tissue cysts were found in their brains, Neosp ora caninum was isolated in cell culture and in gamma-interferon gene knock out mice inoculated with brain homogenates of infected gerbils. The DNA obt ained from fecal oocysts of the dog, from the brains of gerbils fed dog fec es, and from organisms isolated in cell cultures inoculated with gerbil bra ins was confirmed as N. caninum. The identification of N. caninum oocyst by bioassay and polymerase chain reaction demonstrates that the dog is a natu ral definitive host for N. caninum.