Immunopathogenesis and diagnostics of Sarcocystis calchasi in pigeons

卡氏肉孢子虫是鸽子原虫脑炎(PPE)的病原体，PPE是鸽子的一种严重的神经系统疾病。其他中间宿主是鹦鹉和可能的啄木鸟。近年来，世界范围内报告了几次严重的埃博拉疫情。在上一个DFG资助的项目“一种新的鸽子肉孢子虫的流行病学、宿主谱和诊断”中，它在德国各地的赛鸽群中被检测到高患病率(27.8%)。无病原体存在的炎症性脑损伤是PPE的典型表现。其致病机制目前尚不清楚，可作为其他病因不明的脑炎的模型。双重免疫调节可能是Calchasi的一个独特特征，在脑炎早期和分裂相免疫逃避，在脑炎晚期诱导自身免疫。目前，只有通过肌肉活检才能诊断活鸽子和鹦鹉的PPE。该项目旨在确定免疫逃避的机制，并测试卡氏链球菌致脑炎的触发机制。将在鸽子中进行路径分析，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性疾病的替代假设。未来描述分子致病机制的项目可能会以这些结果为基础。该项目的一个重要焦点是确定相关的表面蛋白和其他可能与复杂的寄生虫-宿主相互作用相关的蛋白。这一结果有望广泛加深对PPE免疫发病机制的了解。建立针对Calchasi的特异性血清-ELISA旨在取代肌肉活检的侵入性检测。作为测试抗原，之前确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Calchasi的免疫反应，并可能了解抗体发展在免疫发病机制中的作用。此外，还将确定德国范围内卡氏沙门氏菌抗体在鸽子中的流行情况。最后，我们将讨论卡氏沙门氏菌是否使用更广泛的中间宿主。为此，将在最终宿主的更多猎物物种--苍鹰和雀鸟身上测试S.calchasi的发生。总的来说，拟议项目的各个方面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，这种疾病也具有潜在的重要性，可以用来模拟其他具有复杂免疫病理机制的神经系统疾病。

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.