Tissue and blood stages of avian haemosporidian parasites

Protozoal parasites of the genera Haemoproteus and Leucocytozoon cause frequent infections in wild birds. Their pathogenicity is predominantly inferred by tissue stages of these parasites, known as meronts or megalomeronts. Many aspects of the formation of these stages and their contribution to pathogenicity are unclear. In order to elucidate some of these aspects, this study focuses on four objectives: (1) We assume that exo-erythrocytic merogony and formation of megalomeronts is restricted to few specialized host cell types in different tissues, such as endothelial cells and macrophages. Double labelling with in situ hybridization probes against parasite stages and host cell-specific transcripts will investigate the presence of the parasites in the above-mentioned cell types. (2) The maturity of tissue stages is reflected by variations in staining intensities with haematoxilin and eosin as well as with in situ hybridization. To check whether this phenomenon is due to differential regulation of transcriptional and translational activity associated with changes in ribosomal RNA quantities we plan ultrastructural examination using transmission electron microscopy and qPCR to comparatively analyse the ribosomal RNA content of these structures. (3) It seems possible that megalomeronts or other tissue meronts are persisting stages enabling the survival of Haemoproteus and Leucocytozoon parasites during the cold (vector-free) season. By examining multiple tissue sections of PCR-positive birds obtained during winter with microscopy and in situ hybridization we plan to look for the above mentioned or probably other very small and scarce tissue stages which may be associated with parasite persistence. (4) Sporadic observations suggest that blood stages of avian haemosporidian parasites are sequestrated in the microvasculature of certain organs like in human P. falciparum infections. Cases of Haemoproteus and Leucocytozoon infections will be systematically investigated for uneven distribution of erythrocytic meronts in their micro- and macrovasculature in order to gain solid proof for this assumption. The proposed research questions are of importance because they have not been addressed previously or were not explored in a convincing manner. Principal investigator is Herbert Weissenböck, professor and head of pathology at the University of Veterinary Medicine Vienna. He is an expert in molecular identification of pathogens in tissue samples and heads a research group on pathogenesis of avian haemosporidians. The project team will be complemented by two experienced postdocs. Certain project parts will be investigated in close cooperation with Gediminas Valkiunas from Nature Research Centre Vilnius, Lithuania, one of the world leading experts in avian haemosporidian research.