Immunopathogenesis and diagnostics of Sarcocystis calchasi in pigeons

• Applicants: Professor Achim Dieter Gruber, Ph.D.; Professor Dr. Michael Lierz
• Subject Area: Veterinary Medical Science
• Term: from 2011 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 212404166

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.

• DFG Programme: Research Grants