Avian malaria parasites are a widespread group of vector-transmitted blood parasites (Haemosporida; transmitted to birds primarily by mosquitoes and biting midges). As is the case with human malaria, these parasites can cause severe problems for infected birds. However, avian malaria parasites are not well studied in Australia, so we don't have a good understanding of how common they are or which bird species are important carriers.
Filarial nematodes are also vector-transmitted parasites that can co-infect birds alongside malaria. These worms cause anemia and can cause strong immune responses in birds, but they have been less well-studied compared to malaria parasites.