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Further insights into the pathogenesis of avian malaria

There is increasing evidence that avian haemosporidian parasites (genera of Plasmodium, Haemoproteus and Leucocytozoon) are not only benign commensals but are frequently responsible for lethal infections in birds. Pathogenicity is predominantly inferred by tissue stages of these parasites, which develop in different cell types and lead to blockage of blood vessels and tissue damage. Currently, there is only fragmented knowledge on long-term persistence of these infections and the existence of dormant parasite stages, on the cell types which are targets of replicative tissue stages, on the effect of mixed infections on tissue damage, and finally the question whether 18S ribosomal RNA is differentially expressed in certain developmental stages of the avian malaria parasites.

This study sets out to test the following hypotheses: (1) In analogy to primate malaria parasites, avian haemosporidia also exhibit genetically different 18S ribosomal RNA variants in hosts (birds) and vectors (mosquitoes or biting midges). (2) Relapses in avian malaria are caused by dormant tissue stages which can be visualized by sufficiently sensitive molecular detection methods. (3) Exo-erythrocytic merogony of avian haemosporidian parasites is restricted to few specialized host cell types in different tissues and is more destructive in co-infections.

First, differentially expressed 18 rRNA variants will be labelled by variant-specific probes in avian hosts and arthropod vectors. These results form the basis for the consecutive project parts. The search for dormant stages will be pursued by a highly sensitive in situ hybridization procedure in experimentally infected canaries. The host cell types supporting propagation of parasites in different tissues will be identified by double labelling approaches with antibodies for certain cell markers and molecular probes for haemosporidian meronts. In addition, the effect of mixed infections with two or more haemosporidian species will be tested by double staining procedures.

The majority of the proposed research questions have not been addressed previously (dormant stages and differential expression of rRNAs in avian malaria) or were not explored in a comparably convincing manner, like the identification of cell types allowing propagation of avian malaria parasites, or the effects of mixed infections on the severity of tissue damage.

Project staff:
Univ.-Prof. Dr. Herbert Weissenböck, Dipl.ECPHM, PI
Dr. Josef Harl, Postdoc
MMag. Tanja Himmel PhD, Postdoc

Cooperation partners:
Dr. Gediminas Valkiunas, Mikas Ilgunas, PhD, Nature Research Centre, Vilnius, Lithuania

Project period: 10/2020 - 09/2023

FWF - Austrian Science Fund