Comparative pathogenesis of neosporosis and toxoplasmosis in Australian marsupials

Abstract

Clinical and subclinical Neospora caninum and Toxoplasma gondii infections are reported in many animal species globally, including in Australia where little is known about the impact of parasite infection for native fauna. The investigations in this thesis were designed to fill existing knowledge gaps about the significance of neosporosis and toxoplasmosis in Australian marsupials. The fat-tailed dunnart (Sminthopsis crassicaudata) was used as an experimental model to study the immune response and susceptibility to infection of a native marsupial to N. caninum and T. gondii. Neospora-infected dunnarts had significantly more severe clinical and histopathological features of disease, higher tissue parasite burdens, and a less effective Th1 immune response than Toxoplasma-infected dunnarts. These results indicated the marsupial immune response may play a protective role in parasite infections analogous to what has been shown for eutherian models. This study was the first investigation of the marsupial immune response to N. caninum and T. gondii infection. To better understand toxoplasmosis and its significance in Australian wildlife, cases of naturally occurring disease were investigated in terrestrial and marine mammals. Clinicopathological features of disease were described and the causal parasite strains were genotyped. This work suggested that T. gondii may pose a disease threat to common wombats (Vombatus ursinus) and native marine fauna. Atypical and type II-like T. gondii strains accounted for all cases of toxoplasmosis investigated. Finally, to contextualize the possible significance of N. caninum for Australian wildlife, parasite-associated pathology in wildlife was comprehensively reviewed. As a whole, this thesis contributes substantial original knowledge about marsupial host-parasite interactions, pathological consequences of neosporosis and toxoplasmosis in native marsupials, and genetic diversity of T. gondii circulating in Australian wildlife.