Narelle Dybing

Introduced animals impact ecosystems due to predation, competition and disease transmission. The effect of introduced infectious disease on wildlife populations is particularly pronounced on islands where parasite populations are characterised by increased intensity, infra-community richness and prevalence (the “Island Syndrome”). This thesis studied parasite and bacterial pathogens of conservation and zoonotic importance in feral cats from two islands (Christmas Island, Dirk Hartog Island) and one mainland location (southwest Western Australia), and in black rats from Christmas Island. The general hypothesis tested was that Island Syndrome increases the risk of transmission of parasitic and bacterial diseases introduced/harboured by cats and rats to wildlife and human communities. To investigate the Island Syndrome, necropsies were performed on feral cats and black rats and the macro parasites identified were collected and quantified to ascertain parasite prevalence, infra-community richness and intensity. On Christmas Island, it was determined that 92% of feral cats and 84% of rats harboured helminth parasites with an infra-community richness of 0-6, and 0-7, species in cats and rats, respectively. A high intensity (number of individual parasites recovered per host) was observed for some parasite species. These findings demonstrated that three epidemiological characteristics (high prevalence, infra-community richness and intensity/abundance) conformed to the characteristics of the Island Syndrome. However, contrary to the Island Syndrome hypothesis, a high regional richness of parasites was observed on Christmas Island, with nine species of helminth recorded in cats and 10 species in rats). The parasite community characteristic observations were repeated on Dirk Hartog Island, which also exhibited the same three characteristics of Island Syndrome (high prevalence, infra-community richness and intensity/abundance), but where no difference in regional richness was observed compared with the mainland environment. Specifically, the overall prevalence was significantly higher (p≤0.01) on Dirk Hartog Island (100%) compared to southwest WA (79.6%), as was mean infra-community richness (p≤0.001) (3.61±1.41 on Dirk Hartog Island and 1.57±1.29 from southwest WA). For those parasite species occurring on Dirk Hartog Island and in southwest WA, the prevalence and abundance was found to be significantly higher on Dirk Hartog Island than the southwest WA (p≤0.019 and p≤0.003, respectively). These findings suggest that not all facets proposed by the Island Syndrome hypothesis apply to all island environments, particularly for parasite communities harboured by invasive species. Parasites of both zoonotic and conservation significance were detected in the cats and rats from both islands and from mainland Western Australia. Pathogenic bacteria of public health importance were identified; two species of Bartonella in rats (Bartonella phoceensis and an unidentified Bartonella species) on Christmas Island, two species Bartonella in cats (B. henselae and B. koehlerae) from southwest Western Australia, and Leptospira interrogans from both cats and rats on Christmas Island. The presence of Trypanosoma in cats and rats (from all three locations) and Leishmania (Christmas Island only) were investigated, with neither of these vector-borne protozoans identified at any of the locations. In summary, this thesis presents new data pertaining to parasite community structures in two invasive mammalian pest species of global importance following their introduction to islands, and the potential relationship between their parasite community structures and parasite biology, prevailing physiographic factors and faunal biology. The observations suggest that cats and rats are important in contributing to and maintaining artificially elevated parasite species’ richness within both insular and mainland environments. The findings also highlight potential threats that invasive animals pose with respect to disease transmission to susceptible ecological communities, in particular insular ecosystems, as reservoir hosts for parasitic and bacterial organisms.

Red foxes (Vulpes vulpes) and feral cats (Felis catus) are present throughout a wide range of habitats and landscapes across much of Australia. In addition to the competition and predatory impacts of these two pest species, red foxes and feral cats harbour a wide range of parasites, many of which may have important conservation, agricultural and zoonotic repercussions. This project investigated the occurrence of helminth parasites from the intestines of 147 red foxes and 47 feral cats collected from 14 and 11 locations respectively, throughout southwest Western Australia. Helminth parasites were detected in 58% of foxes and 81% of cats. Helminth species identified from red foxes were: Dipylidium caninum (27.7% of individual foxes examined), Uncinaria stenocephala (18.2%), Toxocara canis (14.9%), Spirometra erinaceieuropaei (5.4%), Toxascaris leonina (4.7%), Taenia spp. (4.1%), Taenia serialis (1.4%), Taenia hydatigena (0.7%), Brachylaima cribbi (0.7%), Plagiorchis maculosus (0.7%) and an Acanthocephalan identified to family Centrorhynchidae (2.1%). Helminth species identified from feral cats were: Taenia taeniaeformis (39.1% of individual cats examined), Toxocara cati (34.8%), Spirometra erinaceieuropaei (19.6%), Oncicola pomatostomi (15.2%), Toxascaris leonina (6.5%), Dipylidium caninum (6.5%), Ancylostoma spp (2.2%) and the Acanthocephalan Centrorhynchidae (2.2%). Infracommunity richness varied from 1-3 and 1-4 species per host in red foxes and feral cats respectively. Average parasite burdens varied from 1-39 worms across all helminth species. Several environmental factors were significantly related to the presence of some parasites in red foxes. For red foxes, the percentage remnant vegetation cover at each sampling location was significantly positively correlated with the presence of T. canis and U. stenocephala (p<0.001). Average relative humidity was significantly positively correlated with the presence of S. erinaceieuropaei (p<0.001), T. leonina (p<0.01) and U. stenocephala (p<0.01). Five year average minimum temperature had an effect on S. erinaceieuropaei and U. stenocephala (p<0.001). For feral cats, a significant positive correlation was detected between the presence of T. cati and five year annual rainfall (p<0.001) as well as individual head/body length and T. taeniaeformis (p<0.001). Helminth species associations were detected between U. stenocephala and D. caninum, S. erinaceieuropaei, T. canis and T. leonina in red foxes. A significant association was also detected between S. erinaceieuropaei and T. leonina in red foxes. In feral cats helminth species associations were detected between T. taeniaeformis and O. pomatostomi as well as between T. taeniaeformis and T. cati. The only parasite that was positively correlated with body condition (assessed by body mass) was S. erinaceieuropaei in foxes. The species richness within a host was not observed to affect body condition in either foxes or cats. In conclusion, red foxes and feral cats in southwest Western Australia harbour a wide range of helminth parasites, which are of veterinary significance for wildlife and livestock. Control of red foxes and feral cats in this region may therefore provide an important mechanism of control of these parasites. Importantly, Echinococcus granulosus, a parasite of major zoonotic concern, was not recorded in this study.