Prevalence of antibodies to Neospora Caninum in dogs

An IFAT was used to determine the prevalence of Neospora-specific IgG antib odies in serum from Alabama horses. Serum samples (n = 536) were from asymp tomatic horses routinely submitted for equine infectious anaemia virus infe ction testing. We also subjected a 13-year-old horse with CNS disease to ne cropsy examination for isolation and in vitro cultivation of protozoal orga nisms. In antemortem tests, this horse was positive for antibodies to Neosp ora sp. in the IFAT and western immunoblot. Results of the prevalence surve y indicated that IgG antibodies to Neospora were present in 62 (11.5%) of t he 536 serum samples. Endpoint titres for the positive samples were 1:50 (3 5/6.5%), 1:100 (19/3.5%), 1:200 (7/1.3%) and 1:1600 (1/0.2%). Tachyzoites w ere first seen in cultured bovine turbinate cells 32 days after inoculation with spinal cord homogenates from the horse with CNS disease. Tachyzoites reacted with known N. caninum-positive serum from horses, cows, dogs and mi ce, but did not react with murine anti-Toxoplasma gondii or equine anti-Sar cocystis neurona serum. Ultrastructural features of tachyzoites and results of comparison of tachyzoite immunodominant proteins revealed that they wer e identical to those of N. hughesi, a species described recently from a nat urally infected horse. The isolate recovered from the naturally infected ho rse in the present study (designated NAI) is thought to be an isolate of N. hughesi, although confirmation of this awaits additional molecular charact erisation. These results provide some additional evidence that Ai. hughesi is a valid species and that Neospora infections in horses may occur in wide ly separated geographic regions of the United States. (C) 1999 Australian S ociety for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.