Characterization of the Oregon isolate of Neospora hughesi from a horse

Neospora hughesi was isolated in cell cultures inoculated with homogenate o f spinal cord from a horse in Oregon. Tachyzoites of this Oregon isolate of N. hughesi were maintained continuously by cell culture passage and tachyz oites were infective to immunosuppressed mice. Gamma interferon gene knocko ut (KO) mice injected with tachyzoites developed fatal myocarditis and nume rous tachyzoites were seen in lesions. Gerbils (Meriones unguiculatas) inoc ulated with tachyzoites developed antibodies (greater than or equal to1:500 ) as indicated by the Neospora caninum agglutination test but did not devel op clinical signs, and Neospora organisms were not demonstrable in their ti ssues. Tissue cysts were not found in gerbils, nude mice, KO mice, immunosu ppressed outbred Swiss Webster mice, or BALB/c mice injected with the Orego n isolate of N. hughesi. Ultrastructurally. tachyzoites of the Oregon isola te from the myocardium of infected KO mice and from cell culture were simil ar to N. caninum tachyzoites. Western blot analysis using NcSAG1 and NcSRS2 polyclonal and monoclonal antibodies and characterization of the internal transcribed spacer 1 sequences from the equine isolates and different isola tes of N. caninum from dogs and cattle indicated that the Oregon isolate of N. hughesi is distinct from N. caninum isolates from cattle and dogs.