Avian haemosporidians are single-celled eukaryotic blood parasites of birds, which – like human malaria parasites – belong to the group of Apicomplexa. The parasites are transmitted by blood-sucking dipteran vectors and infect both tissue and blood cells of the vertebrate hosts. So far, more than 250 species have been described in the three genera Plasmodium, Haemoproteus, and Leucocytozoon. However, data from DNA barcoding studies suggest that there are likely thousands of undescribed species. Avian haemosporidians occur worldwide (except for circumpolar regions) and infect a high percentage of wild birds. For a long time, it was assumed that the co-evolution of hosts and parasites resulted in good adaptation and that the birds usually do not suffer strongly from infections. Cases of severe diseases and deaths were usually reported from birds from polar regions when exposed to parasites and vectors in warmer regions (e.g. penguins in zoos), or when the parasites are introduced to non-adapted island populations.

Researchers at the Institute of Pathology of the University of Veterinary Medicine Vienna (Vetmeduni Wien) investigate whether avian haemosporidioses (including avian malaria) are causes of severe diseases and deaths in native wild birds. The parasite tissue stages, which precede the blood stages, are morphologically similar among diverse haemosporidians and their determination is problematic, especially in the case of mixed infections. Thus, the focus lies on establishing molecular genetic methods for detecting parasites in the tissue of dead birds and creating reference sequences for DNA barcoding.

So far, blood and tissue samples of more than 2,000 wild birds from the collections of the Institute of Pathology, the Institute of Wildlife Ecology, and the bird clinic have been examined for haemosporidian parasites using molecular genetics and chromogenic in-situ hybridization (CISH). Thereby, about one-third of the investigated bird specimens featured haemosporidian infections. The pathological investigations showed that certain wild bird species native to Austria suffer from severe haemosporidian infections more frequently than previously assumed.

In 2020, a Citizen Science project (“Avian malaria: Reporting and collecting dead songbirds”) was carried out during which citizens of eastern Austria were invited to submit dead birds to the Institute of Pathology for pathological examination. A total of 81 bird carcasses from 27 species were received, and haemosporidian infections were detected in about 31% of the individuals.

In an ongoing FWF project (“Further insights into the pathogenesis of avian malaria”), further aspects of haemosporidian infections in native wild birds are investigated, such as long-term persistence and the presence of dormant parasite stages in the bird hosts.