Immunopathogenesis and diagnostics of Sarcocystis calchasi in pigeons

鸽子原生动物脑炎（PPE）是鸽子中一种严重的神经系统疾病。其他中间寄主是鹦鹉，可能还有啄木鸟。近年来，世界各地报道了几次严重的该病暴发。在之前德国联邦政府资助的项目“鸽子中一种新型肉囊菌的流行病学、宿主谱和诊断”中，它在德国各地赛鸽场的发病率很高（27.8%）。没有病原体存在的炎症性脑损伤是典型的个人防护装备。病因机制目前尚不清楚，可以作为其他病因不明的脑病的模型。双重免疫调节可能是脑膜炎球菌的独特特征，在脑炎的早期分裂期免疫逃避，在脑炎的晚期诱导自身免疫。在活鸽子和鹦鹉中诊断个人防护装备目前只能通过肌肉活检进行检测。本项目旨在确定免疫逃避的机制，并测试葡萄球菌诱发脑炎的触发机制。将对鸽子进行途径分析，以确定寄生虫可能的操纵。作为脑炎的可能触发因素，将测试两种关于肇事逃逸机制与免疫介导疾病的替代假设。未来描述分子病理机制的项目可能建立在这些结果的基础上。该项目的一个重点是鉴定相关的表面蛋白和其他可能与复杂的寄生虫-宿主相互作用有关的蛋白。该结果有望广泛加深对PPE免疫发病机制的认识。开发一种针对calchasi的血清elisa特异性方法旨在取代通过肌肉活检进行的侵入性检测。作为测试抗原，先前鉴定的蛋白质将被重组合成。抗体的检测将有助于更好地了解宿主对金黄色葡萄球菌的免疫反应，并可能了解抗体的发展在免疫发病机制中的作用。此外，还将确定德国范围内鸽子中S. calchasi抗体的流行情况。最后，我们将讨论S. calchasi是否使用更广泛的中间宿主。为此，将在最终寄主的其他猎物物种——苍鹰和雀鹰身上测试是否会发生S. calchasi。总的来说，拟议项目的所有方面都将有助于理解和更好地控制这种新的、广泛的和重要的疾病，这对其他具有复杂免疫病理机制的神经系统疾病的建模也具有潜在的重要性。

Sarcocystis calchasi is the cause of pigeon protozoal encephalitis (PPE), a severe neurological disease in pigeons. Further intermediate hosts are psittacines and presumably woodpeckers. In recent years, several severe outbreaks of the disease have been reported world-wide. In the previous DFG-funded project “Epidemiology, host spectrum and diagnostics of a novel Sarcocystis species in pigeons”, its occurrence was detected at a high prevalence (27.8%) in racing pigeon lofts all over Germany. Inflammatory brain lesions without the presence of the pathogen are typical of PPE. The causal pathomechanism is currently not understood and could serve as a model for other encephalitides with unknown aetiologies. A dual immune modulation may be a unique feature of S. calchasi with an immune evasion in the early, schizogonic phase, and an induction of autoimmunity in the late phase of encephalitis. The diagnosis of PPE in live pigeons and parrots is currently only possible by testing a muscle biopsy. The proposed project aims to identify mechanisms of immune evasion and to test the trigger mechanism of S. calchasi-induced encephalitis. A pathway analysis in the pigeon will be conducted to identify possible manipulations by the parasite. As possible triggers of the encephalitis, two alternative hypotheses of a hit-and-run mechanism versus an immune-mediated disease will be tested. Future projects to characterise the molecular pathomechanisms may build on these results. A strong focus of the project is the identification of relevant surface proteins and other proteins that may be associated with the complex parasite-host interaction. The results are expected to widely deepen the understanding of the immunopathogenesis of PPE.The development of a serum-ELISA specific for S. calchasi aims to replace the invasive testing via muscle biopsy. As test antigens, previously identified proteins will be recombinantly synthesised. Detection of antibodies will lead to a better understanding of the host immune-reaction to S. calchasi and possibly the role of antibody development in the immunopathogenesis. Furthermore, the German-wide prevalence of S. calchasi antibodies in pigeons will be determined.Finally, we will address whether S. calchasi uses a broader spectrum of intermediate hosts. To this end, the occurrence of S. calchasi will be tested in further prey species of the final hosts, the goshawk and sparrowhawk.Overall, all aspects of the proposed project will aid in the understanding and better control of this new, widespread and important disease which also possesses potential importance for modelling other neurological diseases with complex immunopathomechanisms.