Serologic survey for Toxoplasma gondii and Neospora caninum in the common brushtail possum (Trichosurus vulpecula) from urban Sydney, Australia

Serological investigation of protozoan pathogens (Trypanosoma cruzi, Toxoplasma gondii and Neospora caninum) in opossums from southern Brazil

South American opossums of the order Didelphimorphia are considered sentinels for zoonotic infections and environmental diseases, such as for Chagas disease caused by Trypanosoma cruzi. Nevertheless, there is a paucity of data regarding protozoan diseases such Toxoplasma gondii and Neospora caninum in Neotropical marsupials; despite these pathogens have been considered threats to some marsupial species. The aim of this study was to determine whether Didelphis albiventris and Philander frenatus opossums from southern Brazil had been previously exposed to T. cruzi, T. gondii or N. caninum. Opossum samples were obtained by live-trapping of free-ranging animals and collection at wildlife rehabilitation centers in Rio Grande do Sul (RS) state, Brazil. The detection of anti-T. cruzi and anti-T. gondii antibodies was performed by indirect hemagglutination and anti-N. caninum antibodies by competitive enzyme-linked immunosorbent assay. In total, samples were collected from 76 marsupials from nine municipalities in RS state, including 69 D. albiventris (white-eared opossum), and seven were P. frenatus (southern four-eyed opossum). For T. cruzi, 11% were seropositive, and for T. gondii 26% were seropositive. None of the marsupials sampled here were seropositive for N. caninum. Risk factor analysis showed that free-living animals were about five-fold more likely to be infected by T. gondii than were rescued animals. Our study showed the exposure of Neotropical marsupials (D. albiventris and P. frenatus) to protozoan pathogens T. cruzi and T. gondii, while no evidence of N. caninum exposure was found. The set of results presented here may have an effect on ecology and conservation of the studied species and may also indicate possible sentinels of these pathogen circulation.

A Case of Letting the Cat out of The Bag-Why Trap-Neuter-Return Is Not an Ethical Solution for Stray Cat (Felis catus) Management

Trap-Neuter-Return (TNR) programs, in which stray cats are captured, neutered and returned to the environment are advocated as a humane, ethical alternative to euthanasia. We review the TNR literature in light of current debate over whether or not there should be further TNR trials in Australia. We revisit the problems arising from stray cats living in association with human habitation and estimate how many stray cats would have to be processed through a scientifically-guided TNR program to avoid high euthanasia rates. We also identify 10 ethical and welfare challenges that have to be addressed: we consider the quality of life for stray cats, where they would live, whether the TNR process itself is stressful, whether TNR cats are vulnerable to injury, parasites and disease, can be medically treated, stray cats' body condition and diet, and their impacts on people, pet cats, and urban wildlife, especially endemic fauna. We conclude that TNR is unsuitable for Australia in almost all situations because it is unlikely to resolve problems caused by stray cats or meet ethical and welfare challenges. Targeted adoption, early-age desexing, community education initiatives and responsible pet ownership have greater promise to minimize euthanasia, reduce numbers rapidly, and address the identified issues.

Urban environments alter parasite fauna, weight and reproductive activity in the quenda (Isoodon obesulus)

Some wildlife species are capable of surviving in urbanised environments. However, the implications of urbanisation on wildlife health, and public health regarding zoonoses, are often unknown. Quenda (syn. southern brown bandicoots, Isoodon obesulus) survive in many areas of Perth, Australia, despite urbanisation. This study investigated differences in gastrointestinal and macroscopic ecto-parasitic infections, morphometrics and reproductive status between bushland and urban dwelling quenda. 287 quenda in the greater Perth region were captured and sampled for faeces (to detect gastrointestinal parasites), blood (to detect Toxoplasma gondii antibodies), ectoparasites, and morphometrics. Data were analysed using multivariable logistic and linear regression. Most parasitic infections identified in quenda were of native parasite taxa that are either not known to, or considered highly unlikely to, infect humans or domestic animals. However, stickfast fleas (Echidnophaga spp.) were present at low prevalences and intensities, and Giardia spp., Cryptosporidium spp. and Amblyomma spp. infections require further investigation to clarify their anthropozoonotic significance. Quenda captured in urbanised environments had differing odds of or intensity of certain parasitic infections, compared to those in bushland - likely attributable to quenda population density, and in some cases the availability of other host species or anthropogenic sources of infection. Urbanised environments were associated with an increase in net weight of adult male quenda by 189.0g (95% CI 68.6-309.5g; p=0.002; adjusted R²=0.06) and adult female quenda by 140.1g (95% CI 3.9-276.3g; p=0.044; adjusted R²=0.07), with study findings suggesting a tendency towards obesity in urbanised environments. Adult female quenda in bushland had increased odds of an active pouch (adjusted OR=4.89, 95% CI 1.7-14.5), suggesting decreased reproductive activity in quenda from urbanised environments. These results highlight the subtle, yet extensive impacts that urbanised environments may have on wildlife ecology, even for those species which apparently adjust well to urbanisation.

Differential Gamma Interferon- and Tumor Necrosis Factor Alpha-Driven Cytokine Response Distinguishes Acute Infection of a Metatherian Host with Toxoplasma gondii and Neospora caninum

Toxoplasma gondii and Neospora caninum (both Apicomplexa) are closely related cyst-forming coccidian parasites that differ significantly in their host ranges and ability to cause disease. Unlike eutherian mammals, Australian marsupials (metatherian mammals) have long been thought to be highly susceptible to toxoplasmosis and neosporosis because of their historical isolation from the parasites. In this study, the carnivorous fat-tailed dunnart (Sminthopsis crassicaudata) was used as a disease model to investigate the immune response and susceptibility to infection of an Australian marsupial to T. gondii and N. caninum The disease outcome was more severe in N. caninum-infected dunnarts than in T. gondii-infected dunnarts, as shown by the severity of clinical and histopathological features of disease and higher tissue parasite burdens in the tissues evaluated. Transcriptome sequencing (RNA-seq) of spleens from infected dunnarts and mitogen-stimulated dunnart splenocytes was used to define the cytokine repertoires. Changes in mRNA expression during the time course of infection were measured using quantitative reverse transcription-PCR (qRT-PCR) for key Th1 (gamma interferon [IFN-γ] and tumor necrosis factor alpha [TNF-α]), Th2 (interleukin 4 [IL-4] and IL-6), and Th17 (IL-17A) cytokines. The results show qualitative differences in cytokine responses by the fat-tailed dunnart to infection with N. caninum and T. gondii Dunnarts infected with T. gondii were capable of mounting a more effective Th1 immune response than those infected with N. caninum, indicating the role of the immune response in the outcome scenarios of parasite infection in this marsupial mammal.

Is Toxoplasma gondii a threat to the conservation of free-ranging Australian marsupial populations?

It has often been asserted that Australian marsupial species are particularly susceptible to Toxoplasma gondii infection and to clinical toxoplasmosis following infection. This implicates T. gondii as a potential threat to marsupial population viability, and contrasts to what is known of T. gondii in populations of several other host species. We reviewed the literature, and found a lack of scientifically robust evidence addressing the occurrence of T. gondii infection in free-ranging populations of Australian marsupial species, and the impacts of the infection on population health. Key limitations included a lack of studies in free-ranging marsupial populations, study findings susceptible to substantial chance influences, and selection, misclassification and confounding biases. The lack of scientifically robust data available on this topic indicates that assertions that free-ranging populations of Australian marsupials are particularly susceptible to T. gondii infection and to toxoplasmosis are premature. The threat of T. gondii to the viability of free-ranging marsupial populations should therefore be regarded, at this stage, as a hypothesis.

Beyond the disease: Is Toxoplasma gondii infection causing population declines in the eastern quoll (Dasyurus viverrinus)?

Disease is often considered a key threat to species of conservation significance. For some, it has resulted in localised extinctions and declines in range and abundance. However, for some species, the assertion that a disease poses a significant threat of extinction is based solely on correlative or anecdotal evidence, often inferred from individual clinical case reports. While a species' susceptibility to a disease may be demonstrated in a number of individuals, investigations rarely extend to measuring the impact of disease at the population level and its contribution, if any, to population declines. The eastern quoll (Dasyurus viverrinus) is a medium-sized Australian marsupial carnivore that is undergoing severe and rapid decline in Tasmania, its last refuge. Reasons for the decline are currently not understood. Feral cats (Felis catus) may be undergoing competitive release following the ongoing decline of the Tasmanian devil (Sarcophilus harrisii), with cats suppressing eastern quolls through increased predation, competition, exclusion or exposure to diseases such as toxoplasmosis. To investigate the effects of Toxoplasma gondii infection, eastern quoll populations at four sites were regularly screened for the seroprevalence of T. gondii-specific IgG antibodies. Seroprevalence was approximately five times higher at sites with declining quoll populations, and there was a negative association between seroprevalence and quoll abundance. However, T. gondii infection did not reduce quoll survival or reproduction. Despite a high susceptibility to T. gondii infection, eastern quoll populations do not appear to be limited by the parasite or its resultant disease. Significantly higher seroprevalence is a signal of greater exposure to feral cats at sites where eastern quolls are declining, suggesting that increased predation, competition or exclusion by feral cats may be precipitating population declines.

Canine rabies in Australia: a review of preparedness and research needs

Australia is unique as a populated continent in that canine rabies is exotic, with only one likely incursion in 1867. This is despite the presence of a widespread free-ranging dog population, which includes the naturalized dingo, feral domestic dogs and dingo-dog cross-breeds. To Australia's immediate north, rabies has recently spread within the Indonesian archipelago, with outbreaks occurring in historically free islands to the east including Bali, Flores, Ambon and the Tanimbar Islands. Australia depends on strict quarantine protocols to prevent importation of a rabid animal, but the risk of illegal animal movements by fishing and recreational vessels circumventing quarantine remains. Predicting where rabies will enter Australia is important, but understanding dog population dynamics and interactions, including contact rates in and around human populations, is essential for rabies preparedness. The interactions among and between Australia's large populations of wild, free-roaming and restrained domestic dogs require quantification for rabies incursions to be detected and controlled. The imminent risk of rabies breaching Australian borders makes the development of disease spread models that will assist in the deployment of cost-effective surveillance, improve preventive strategies and guide disease management protocols vitally important. Here, we critically review Australia's preparedness for rabies, discuss prevailing assumptions and models, identify knowledge deficits in free-roaming dog ecology relating to rabies maintenance and speculate on the likely consequences of endemic rabies for Australia.

Regional seroprevalence of Toxoplasma gondii antibodies in feral and stray cats (Felis catus) from Tasmania

Toxoplasma gondii is a cosmopolitan protozoan parasite of felids that also has significant implications for the health of wildlife, livestock and humans worldwide. In Australia, feral, stray and domestic cats (Felis catus) are the most important definitive host of T. gondii as they are the only species that can excrete the environmentally resistant oocysts that provide a major source of infection for mammals and birds. In Tasmania, the rapid decline of the Tasmanian devil (Sarcophilus harrisii) may allow an increase in feral cat abundance, thereby increasing the risk of T. gondii infection to a range of susceptible wildlife species. At present, there is scant information on the prevalence of T. gondii infection in feral cat populations across Tasmania. We tested feral cats from 13 regions across Tasmania for the presence of T. gondii–specific IgG antibodies using a modified agglutination test. Results were combined with serosurveys from three previous studies to enable a comparison of seroprevalence among 14 regions across Tasmania. We found that 84.2% (224 of 266) of cats tested positive for T. gondii IgG antibodies. This is among the highest rates of prevalence recorded from Australia, and significantly higher than for most other countries. Adult cats had higher seroprevalence than kittens but there was no difference between sexes. In Tasmania, seroprevalence was high in 12 of 14 regions (range: 79.3–100.0%), with only two regions (Tasman Island and Southern Tasmania) recording significantly lower seroprevalence (≤50%). This suggests a high risk of infection across Tasmania, and has significant implications for wildlife conservation should feral cat abundance increase with the ongoing declines in Tasmanian devils.

Neospora caninum and Wildlife

Bovine neosporosis caused by Neospora caninum is among the main causes of abortion in cattle nowadays. At present there is no effective treatment or vaccine. Serological evidence in domestic, wild, and zoo animals indicates that many species have been exposed to this parasite. However, many aspects of the life cycle of N. caninum are unknown and the role of wildlife in the life cycle of N. caninum is still not completely elucidated. In North America, there are data consistent with a sylvatic cycle involving white tailed-deer and canids and in Australia a plausible sylvatic cycle could be occurring between wild dogs and their macropod preys. In Europe, a similar sylvatic cycle has not been established but is very likely. The present review is a comprehensive and up to date summary of the current knowledge on the sylvatic cycle of N. caninum, species affected and their geographical distribution. These findings could have important implications in both sylvatic and domestic cycles since infected wildlife may influence the prevalence of infection in cattle farms in the same areas. Wildlife will need to be taken into account in the control measures to reduce the economical losses associated with this important disease in cattle farms.

Wildlife disease ecology in changing landscapes: Mesopredator release and toxoplasmosis

Changing ecosystem dynamics are increasing the threat of disease epidemics arising in wildlife populations. Several recent disease outbreaks have highlighted the critical need for understanding pathogen dynamics, including the role host densities play in disease transmission. In Australia, introduced feral cats are of immense concern because of the risk they pose to native wildlife through predation and competition. They are also the only known definitive host of the coccidian parasite, Toxoplasma gondii, the population-level impacts of which are unknown in any species. Australia’s native wildlife have not evolved in the presence of cats or their parasites, and feral cats may be linked with several native mammal declines and extinctions. In Tasmania there is emerging evidence that feral cat populations are increasing following wide-ranging and extensive declines in the apex predator, the Tasmanian devil, from a consistently fatal transmissible cancer.

We assess whether feral cat density is associated with the seroprevalence of T. gondii in native wildlife to determine whether an increasing population of feral cats may correspond to an increased level of risk to naive native intermediate hosts. We found evidence that seroprevalence of T. gondii in Tasmanian pademelons was lower in the north-west of Tasmania than in the north-east and central regions where cat density was higher. Also, samples obtained from road-killed animals had significantly higher seroprevalence of T. gondii than those from culled individuals, suggesting there may be behavioural differences associated with infection. In addition, seroprevalence in different trophic levels was assessed to determine whether position in the food-web influences exposure risk. Higher order carnivores had significantly higher seroprevalence than medium-sized browser species. The highest seroprevalence observed in an intermediate host was 71% in spotted-tailed quolls (Dasyurus maculatus), the largest mammalian mesopredator, in areas of low cat density. Mesopredator release of cats may be a significant issue for native species conservation, potentially affecting the population viability of many endangered species.

Neosporosis in a captive Parma wallaby (Macropus parma)

Infection with Neospora caninum has been diagnosed in a variety of animal species; however, reports in marsupials are rare. A captive Parma wallaby (Macropus parma) died suddenly and was subjected to necropsy examination. The main finding was necrotizing myocarditis associated with protozoan parasites. The protozoa were identified as N. caninum by use of immunohistochemistry and partial gene sequence analysis. Neospora and Toxoplasma should be considered a possible cause of disease in captive marsupials. Further work is required to determine whether marsupials are an accidental or terminal host of this protozoan in order to better understand the host-parasite relationship.

Cat-exclusion zones in rural and urban-fringe landscapes: how large would they have to be?

Context. The process of urban sprawl brings the human population and their domestic cats (Felis catus) in close contact with wildlife in areas that were previously remote, including reserves and conservation areas created to protect populations of vulnerable or threatened species. Various mitigation measures have been proposed, including devices designed to hinder cat hunting ability, desexing to reduce wandering and nuisance behaviours, containment at night or at all times and regulations governing cat ownership. Such regulations may aim to reduce cat densities by limiting the number of cats per household, or they may define zones around sensitive conservation areas where cat ownership is prohibited. Aims. The present study sought to establish the necessary size of cat-exclusion zones in rural and urban-fringe landscapes where vulnerable prey species may also reside. Methods. With GPS collars, we tracked 38 domestic cats at three sites (one rural, two urban fringe) where small reserves contained threatened lizard species. Key results. Home ranges (95% kernel density estimates) were considerably larger for cats at the rural site (0.3–69 ha) than at urban-fringe sites (0.35–19 ha at Kaitorete Spit and 0.2–9 ha at Otago Peninsula), and were larger at night than day. Resource selection ratios indicated avoidance of open areas with little cover, such as cultivated areas (farmland), tussock grassland and duneland, whereas sources of cover such as trees and buildings were preferred. Maximum distances moved and large variability between individual cats suggest buffers in rural landscapes would need to be at least 2.4 km wide, whereas those in urban-fringe habitat could be half as large. Conclusions. Despite significant home-range size differences exhibited by cats living in rural v. urban-fringe habitats, exclusion zones would need to be wide to account for considerable inter-cat variation in movement behaviour. Implications. The size of an effective cat-exclusion zone should represent the specific landscape, amount of residential development and substantial variability between individual cats.

Seroprevalence of Toxoplasma gondii in wild kangaroos using an ELISA

Infection with Toxoplasma gondii is a significant problem in Australian marsupials, and can lead to devastating disease and predispose animals to predation. T. gondii infection in kangaroos is also of public health significance due to the kangaroo meat trade. A moderate seroprevalence of T. gondii was observed in a study of western grey kangaroos located in the Perth metropolitan area in Western Australia. Of 219 kangaroos tested, 15.5% (95%CI: 10.7-20.3) were positive for T. gondii antibodies using an ELISA developed to detect T. gondii IgG in macropod marsupials. When compared with the commercially available MAT (modified agglutination test), the ELISA developed was in absolute agreement and yielded a kappa coefficient of 1.00. Of 18 kangaroos tested for the presence of T. gondii DNA by PCR, the 9 ELISA positive kangaroos tested PCR positive and the 9 ELISA negative kangaroos tested PCR negative indicating the ELISA protocol was both highly specific and sensitive and correlated 100% with the more labour intensive PCR assay.

Age of road-killed common brushtail possums (Trichosurus vulpecula) and common ringtail possums (Pseudocheirus peregrinus) in an urban environment

Road-associated mortality has been identified as having major ecological effects on small, fragmented and declining populations. Both the common brushtail possum (Trichosurus vulpecula) and common ringtail possum (Pseudocheirus peregrinus) appear to be in decline in some regions across their natural ranges. Urban populations may be an exception; however, little is known of their population ecology. This study investigates age trends in a subset of road-killed brushtail and ringtail possums collected along eight northern Sydney roads between March 2004 and March 2006. From a total of 591 recorded road-killed possums, 86 were collected for use in this study (36 brushtails, 50 ringtails). Age was estimated using tooth wear patterns on cleaned skulls. Both species showed trends associated with age, and younger possums of both species were more likely to be killed on roads than older animals. Male-biased dispersal of subadult possums is considered a major contributing factor to the over-representation of young brushtail possums in this road-kill sample.

Prevalence and genetic characterization of Cryptosporidium isolates from common brushtail possums (Trichosurus vulpecula) adapted to urban settings

The common brushtail possum (Trichosurus vulpecula) is one of the most abundant native marsupials in urban Australia, having successfully adapted to utilize anthropogenic resources. The habituation of possums to food and shelter available in human settlements has facilitated interaction with people, pets, and zoo animals, increasing the potential for transmission of zoonotic Cryptosporidium pathogens. This study sought to examine the identity and prevalence of Cryptosporidium species occurring in possums adapted to urban settings compared to possums inhabiting remote woodlands far from urban areas and to characterize the health of the host in response to oocyst shedding. Findings indicated that both populations were shedding oocysts of the same genotype (brushtail possum 1 [BTP1]) that were genetically and morphologically distinct from zoonotic species and genotypes and most closely related to Cryptosporidium species from marsupials. The urban population was shedding an additional five Cryptosporidium isolates that were genetically distinct from BTP1 and formed a sister clade with Cryptosporidium parvum and Cryptosporidium hominis. Possums that were shedding oocysts showed no evidence of pathogenic changes, including elevated levels of white blood cells, diminished body condition (body mass divided by skeletal body length), or reduced nutritional state, suggesting a stable host-parasite relationship typical of Cryptosporidium species that are adapted to the host. Overall, Cryptosporidium occurred with a higher prevalence in possums from urban habitat (11.3%) than in possums from woodland habitat (5.6%); however, the host-specific nature of the genotypes may limit spillover infection in the urban setting. This study determined that the coexistence of possums with sympatric populations of humans, pets, and zoo animals in the urban Australian environment is unlikely to present a threat to public health safety.

Epidemiology and control of neosporosis and Neospora caninum

Neospora caninum is a protozoan parasite of animals. Until 1988, it was misidentified as Toxoplasma gondii. Since its first recognition in dogs in 1984 and the description of the new genus and species Neospora caninum in 1988, neosporosis has emerged as a serious disease of cattle and dogs worldwide. Abortions and neonatal mortality are a major problem in livestock operations, and neosporosis is a major cause of abortion in cattle. Although antibodies to N. caninum have been reported, the parasite has not been detected in human tissues. Thus, the zoonotic potential is uncertain. This review is focused mainly on the epidemiology and control of neosporosis in cattle, but worldwide seroprevalences of N. caninum in animals and humans are tabulated. The role of wildlife in the life cycle of N. caninum and strategies for the control of neosporosis in cattle are discussed.

Genetic structure infers generally high philopatry and male-biased dispersal of brushtail possums (Trichosurus vulpecula) in urban Australia

The brushtail possum (Trichosurus vulpecula) is in decline throughout much of its natural range with the notable exception of urban areas and a few islands. In some urban areas, its density can be high enough to cause conflict with householders. We provide the first genetic-based study of dispersal for T. vulpecula in the urban environment. Seven microsatellite markers were used to investigate genetic structure of adult male (n = 53) and female (n = 39) possums sampled from mainland suburbs of Sydney, and on nearby Scotland Island. Samples from Scotland Island also provide an opportunity to assess the effect of isolation on genetic variability, which, as theory would predict, was significantly lower than observed in mainland samples. Male-biased dispersal was inferred from patterns of relatedness between individuals of each sex. Average relatedness was significantly higher between adult female possums than between adult male possums sampled within the same garden area. In addition, males were genotypically more similar to one another at substantially greater geographic distances than females. Along with male-biased dispersal, strong localised genetic structure for both sexes infers generally high philopatry. Dispersal distances were greatest for adult male possums sampled from mainland locations. However, even for these males, genotypic similarity between possums separated by distances further than ~900 m was lower than the sample average, suggesting infrequent dispersal beyond this distance. Knowledge of dispersal patterns is important to managing the density levels of overabundant T. vulpecula in urban areas.