Histologic examination of aborted material is an essential component in the diagnosis of ovine toxoplasmosis. However, the detection of Toxoplasma gondii in histologic sections, and its differentiation from the closely related protozoan Neospora caninum, is challenging. We developed a chromogenic in situ hybridization (ISH) assay for the identification of T. gondii in paraffin-embedded tissue samples. We examined retrospectively the archived placental tissue of 200 sheep abortion submissions for the presence of T. gondii by immunohistochemistry (IHC), ISH, and real-time PCR (rtPCR). All placental samples that tested positive for T. gondii by rtPCR (9 of 200) were also positive by IHC, with inconclusive IHC staining in an additional 7 rtPCR-negative cases. Further testing for N. caninum of all 200 placentas by rtPCR revealed 7 Neospora-positive cases. T. gondii ISH was positive in 4 of 9 IHC-positive samples and 1 of the 7 N. caninum rtPCR-positive samples. Real-time PCR was used as the reference standard for specificity and sensitivity calculations regarding placenta samples. Specificity of ISH and IHC was 99% and 96–100%, respectively. The sensitivity of ISH (44%) was quite low compared to IHC (100%). The exclusive use of ISH for the detection of T. gondii, and thus for the diagnosis of ovine toxoplasmosis, was not acceptable. However, combined with rtPCR, both ISH and IHC can be useful detection methods to improve histologic evaluation by visualizing the parasite within tissue sections.

流产材料的组织学检查是诊断绵羊弓形虫病的重要组成部分。然而，在组织学切片中检测刚地弓形虫及其与密切相关的原生动物新孢子虫的区分具有挑战性。我们开发了一种显色原位杂交 (ISH) 测定法，用于鉴定石蜡包埋组织样本中的弓形虫。我们通过免疫组织化学 (IHC)、ISH 和实时 PCR (rtPCR)回顾性检查了 200 例羊流产提交的存档胎盘组织中弓形虫的存在。所有对刚地弓形虫检测呈阳性的胎盘样本通过 rtPCR（200 个中的 9 个）的 IHC 也呈阳性，另外 7 个 rtPCR 阴性病例的 IHC 染色不确定。通过 rtPCR 对所有 200 个胎盘的犬新孢子虫进行进一步检测，发现 7 个新孢子虫阳性病例。T. gondii ISH 在 9 个 IHC 阳性样本中的 4 个和 7 个N. caninum rtPCR 阳性样本中的 1 个呈阳性。实时荧光定量 PCR 被用作关于胎盘样品的特异性和敏感性计算的参考标准。ISH 和 IHC 的特异性分别为 99% 和 96-100%。与 IHC (100%) 相比，ISH (44%) 的灵敏度相当低。ISH 独家用于检测弓形虫，因此对于羊弓形虫病的诊断，是不可接受的。然而，结合 rtPCR，ISH 和 IHC 都可以成为有用的检测方法，通过可视化组织切片中的寄生虫来改善组织学评估。