Abstract
The brush-tailed bettong (Bettongia penicillata), or woylie, has undergone a rapid and substantial decline throughout its range in the southwest of Western Australia over a period of approximately five years. As part of an investigation into possible causes of the decline, a morphologically distinct Trypanosoma sp. was discovered by light microscopy in the declining population but was not observed in a captive and stable population within the Karakamia Wildlife Sanctuary. Further investigations employing molecular methods targeting variations in the 18s rRNA gene determined that the trypanosome was novel and was also present within the Karakamia population albeit at a much lower overall prevalence and individual parasitemia levels. Phylogenetic analysis suggests the novel Trypanosoma sp. to be closely related to other trypanosomes isolated from native Australian wildlife species. The potential for a trypanosome species to affect the woylie population, singularly as well as in conjunction with other infectious agents as part of a concomitant infection, is discussed.