Narelle Dybing

Australia’s National Feral Pig Action Plan 2021-2031 is the first national strategy to reduce the extensive and diverse impacts caused by feral pigs to Australia’s environmental, agricultural, cultural and social assets by actively suppressing feral pig populations over time. Its development was instigated in response to growing threats of an exotic disease incursion, particularly African swine fever to the Australian pork industry. It provides a national framework for alignment of state, regional and local strategic feral pig management plans. The Plan was endorsed by Australia’s National Biosecurity Committee in October 2021 and aims to encourage land managers to work together in coordinated groups on a landscape scale, cross tenure basis, and strategically apply the most appropriate combinations of best practice management methods for their region (National Feral Pig Action Plan 2021). Its 10-year time frame reflects the long time required to reduce impacts from feral pigs, and their populations, as well as the enormity of the task. Many stakeholders, including governments, agricultural industries, natural resource management organisations, universities, Indigenous organisations, private land managers and not for profit environmental conservation managers are being engaged to support the Plan’s implementation. In Australia, how feral pig management is being undertaken needs to shift from being fragmented, ad hoc and reactive to be more coordinated, collaborative, strategic, and proactive; with activities supported by strong and trusted partnerships between all land managers. This paper discusses several initiatives being undertaken to support the implementation of the National Feral Pig Action Plan 2021-2031. These initiatives are principally directed at improving the efficacy and efficiency of on-ground best practice management actions by land managers by influencing practice and behaviour change and undertaking monitoring to fill significant data and knowledge gaps.

Non-typhoidal Salmonella serovars are recognized as zoonotic pathogens. Although human salmonellosis is frequently associated with ingestion of contaminated foods of animal origin, contact with animals may also be a significant source of Salmonella infection, especially contact with turtles, which have shown to be an important reservoir of Salmonella, specifically through their intestinal tracts. Turtles are among the most common reptiles kept as house pets that may pose a public health risk associated with Salmonella exposure, especially among infants and young children. This review discusses the literature reporting the link between turtles and Salmonella as well as turtle-associated human salmonellosis in the last ten years. In most outbreaks, a high proportion of patients are children under five years of age, which indicates that children are at the greatest risk of turtle-associated salmonellosis. Therefore, turtles should not be preferred as recommended pets for children under five years of age. Reducing turtle stress to minimise Salmonella shedding as well as providing client education handouts at the points of sale of these animals may reduce the risk of transmitting such significant pathogen to humans. Further studies are required to investigate the role of both direct contact with turtles as well as indirect contact through cross-contamination in the transmission of turtles-associated Salmonella to humans.

Many island ecosystems are exposed to ecological threats through invasive species and the parasites they harbour. Parasites can impact endemic island populations whether they are stable populations or ones already in decline. The ‘Island Syndrome’ hypothesis proposes that richness and diversity of introduced parasites differ from mainland populations with lower parasite species diversity on islands due to the founder effect. To examine the role of ‘Island Syndrome’ and impacts for faunal and human communities on a tropical island, helminth parasites were identified from feral cats (Felis catus) (n = 66) and black rats (Rattus rattus) (n = 101) on Christmas Island. Sixty-one (92 per cent) of cats and 85 (84 per cent) of rats harboured one or more helminth species with total infra-community richness (TICR) ranging over zero to six species in cats and zero to seven species in rats, including species of zoonotic significance (Angiostrongylus cantonensis, Toxocara cati, Ancylostoma braziliense, Taenia taeniaeformis, Moniliformis moniliformis and Hymenolepis nana). High parasite prevalence and TICR were expected in island populations; however, high parasite richness in cats and rats on Christmas Island was counter to the ‘Island Syndrome’. These results suggest that introduced cats and rats may be responsible for maintaining an increased parasitological threat to fauna and human communities in certain ecosystems.

Leptospirosis is a neglected, re-emerging bacterial disease with both zoonotic and conservation implications. Rats and livestock are considered the usual sources of human infection, but all mammalian species are capable of carrying Leptospira spp. and transmitting pathogenic leptospires in their urine, and uncertainty remains about the ecology and transmission dynamics of Leptospira in different regions. In light of a recent case of human leptospirosis on tropical Christmas Island, this study aimed to investigate the role of introduced animals (feral cats and black rats) as carriers of pathogenic Leptospira spp. on Christmas Island and to compare this with two different climatic regions of Western Australia (one island and one mainland). Kidney samples were collected from black rats (n = 68) and feral cats (n = 59) from Christmas Island, as well as feral cats from Dirk Hartog Island (n = 23) and southwest Western Australia (n = 59). Molecular (PCR) screening detected pathogenic leptospires in 42.4% (95% confidence interval 29.6–55.9) of cats and 2.9% (0.4–10.2) of rats from Christmas Island. Sequencing of cat- and rat-positive samples from Christmas Island showed 100% similarity for Leptospira interrogans. Pathogenic leptospires were not detected in cats from Dirk Hartog Island or southwest Western Australia. These findings were consistent with previous reports of higher Leptospira spp. prevalence in tropical regions compared with arid and temperate regions. Despite the abundance of black rats on Christmas Island, feral cats appear to be the more important reservoir species for the persistence of pathogenic L. interrogans on the island. This research highlights the importance of disease surveillance and feral animal management to effectively control potential disease transmission.

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.

Trypanosomes and Leishmania are vector-borne parasites associated with high morbidity and mortality. Trypanosoma lewisi, putatively introduced with black rats and fleas, has been implicated in the extinction of two native rodents on Christmas Island (CI) and native trypanosomes are hypothesized to have caused decline in Australian marsupial populations on the mainland. This study investigated the distribution and prevalence of Trypanosoma spp. and Leishmania spp. in two introduced pests (cats and black rats) for three Australian locations. Molecular screening (PCR) on spleen tissue was performed on cats from CI (n = 35), Dirk Hartog Island (DHI; n = 23) and southwest Western Australia (swWA) (n = 58), and black rats from CI only (n = 46). Despite the continued presence of the intermediate and mechanical hosts of T. lewisi, there was no evidence of trypanosome or Leishmania infection in cats or rats from CI. Trypanosomes were not identified in cats from DHI or swWA. These findings suggest T. lewisi is no longer present on CI and endemic Trypanosoma spp. do not infect cats or rats in these locations.

Bacteria of the genus Bartonella have been described in multiple mammalian hosts with many species capable of causing disease in humans. Cats and various species of rats have been reported to play a role as vertebrate hosts to a number of Bartonella spp. This study aimed to identify Bartonella spp. in Western Australia, Dirk Hartog Island (DHI), and Christmas Island (CI) and to investigate the presence of potential arthropod vectors. Feral cats were collected from CI (n = 35), DHI (n = 23) and southwest Western Australia (swWA; n = 58), and black rats were collected from CI (n = 48). Individuals were necropsied, ectoparasites were collected by external examination of carcasses, and splenic tissue was collected for polymerase chain reaction analysis to detect Bartonella DNA. Bartonella henselae DNA was detected from two cats and Bartonella koehlerae DNA from one cat in southwest WA, but Bartonella DNA was not identified in cats on DHI or CI. Bartonella phoceensis (28/48 = 58.3%) and a novel Bartonella genotype (8/48 = 16.7%) based on the internal transcribed space region were detected in the spleens of black rats on CI. Detection of Bartonella spp. in each location corresponded to the presence of ectoparasites. Cats from southwest WA harbored four species of fleas, including Ctenocephalides felis, and black rats on CI were infested with multiple species of ectoparasites, including mites, fleas, and lice. Conversely, cats on Dirk Hartog and CI were free of ectoparasites. This study has identified the DNA of Bartonella species from island and mainland swWA with some (B. henselae and B. koehlerae) of known zoonotic importance. This study further extends the geographical range for the pathogenic B. koehlerae. The association of Bartonella with ectoparasites is unsurprising, but little is known about the specific vector competence of the ectoparasites identified in this study.

Red foxes (Vulpes vulpes) are the most common and widely distributed wild carnivore worldwide. These predators 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 across 14 sampling localities of southwest Western Australia. Helminth parasites were detected in 58% of fox intestines: Dipylidium caninum (27.7% of foxes), Uncinaria stenocephala (18.2%), Toxocara canis (14.9%), Spirometra erinaceieuropaei (5.4%), Toxascaris leonina (4.7%), Taenia serialis (1.4%), Taenia hydatigena (0.7%), unidentified Taenia spp. (4.1%), Brachylaima cribbi (0.7%), Plagiorchis maculosus (0.7%) and an Acanthocephalan; family Centrorhynchidae (2.1%). Importantly, two cestodes of agricultural significance, Echinococcus granulosus and Taenia ovis, were not detected in red foxes in this study, despite the presence of suitable intermediate hosts in the diets of these animals. Parasite richness varied from 1–3 species per host, with average parasite number varying from 1–39 worms (across all helminth species). Regression analyses indicated that the presence of four helminth parasites was related to various environmental factors. The presence of S. erinaceieuropaei (p < 0.001), T. leonina (p < 0.01) and U. stenocephala (p < 0.01) was positively associated with average relative humidity which may affect the longevity of infective stages in the environment. The presence of S. erinaceieuropaei and U. stenocephala (p < 0.001) was positively associated with 5-y-average minimum temperature which could reflect poor survival of infective stages through cold winter conditions. The presence of T. canis and U. stenocephala (p < 0.001) was positively associated with the percentage cover of native vegetation at each sampling location, which is likely to reflect transmission from native prey species acting as paratenic hosts. These data identify environmental factors affecting transmission and potential distribution of each parasite taxon, and provide important information increasing our understanding of the potential effects of environmental change on parasite ecology.

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.