Four Cases of Fatal Toxoplasmosis in Three Species of Endemic New Zealand Birds

Drivers of infection with Toxoplasma gondii genotype type II in Eurasian red squirrels (Sciurus vulgaris)

BACKGROUND

In September 2014, there was sudden upsurge in the number of Eurasian red squirrels (Sciurus vulgaris) found dead in the Netherlands. High infection levels with the parasite Toxoplasma gondii were demonstrated, but it was unclear what had caused this increase in cases of fatal toxoplasmosis. In the present study, we aimed to gain more knowledge on the pathology and prevalence of T. gondii infections in Eurasian red squirrels in the Netherlands, on the T. gondii genotypes present, and on the determinants of the spatiotemporal variability in these T. gondii infections. The presence of the closely related parasite Hammondia hammondi was also determined.

METHODS

Eurasian red squirrels that were found dead in the wild or that had died in wildlife rescue centres in the Netherlands over a period of seven years (2014-2020) were examined. Quantitative real-time polymerase chain reaction was conducted to analyse tissue samples for the presence of T. gondii and H. hammondi DNA. Toxoplasma gondii-positive samples were subjected to microsatellite typing and cluster analysis. A mixed logistic regression was used to identify climatic and other environmental predictors of T. gondii infection in the squirrels.

RESULTS

A total of 178 squirrels were examined (49/178 T. gondii positive, 5/178 H. hammondi positive). Inflammation of multiple organs was the cause of death in 29 squirrels, of which 24 were also T. gondii polymerase chain reaction positive. Toxoplasma gondii infection was positively associated with pneumonia and hepatitis. Microsatellite typing revealed only T. gondii type II alleles. Toxoplasma gondii infection rates showed a positive correlation with the number of days of heavy rainfall in the previous 12 months. Conversely, they showed a negative association with the number of hot days within the 2-week period preceding the sampling date, as well as with the percentage of deciduous forest cover at the sampling site.

CONCLUSIONS

Toxoplasma gondii infection in the squirrels appeared to pose a significant risk of acute mortality. The T. gondii genotype detected in this study is commonly found across Europe. The reasons for the unusually high infection rates and severe symptoms of these squirrels from the Netherlands remain unclear. The prevalence of T. gondii in the deceased squirrels was linked to specific environmental factors. However, whether the increase in the number of dead squirrels indicated a higher environmental contamination with T. gondii oocysts has yet to be established.

More people, more cats, more parasites: Human population density and temperature variation predict prevalence of Toxoplasma gondii oocyst shedding in free-ranging domestic and wild felids

Toxoplasma gondii is a ubiquitous zoonotic parasite that can infect warm-blooded vertebrates, including humans. Felids, the definitive hosts, drive T. gondii infections by shedding the environmentally resistant stage of the parasite (oocysts) in their feces. Few studies characterize the role of climate and anthropogenic factors in oocyst shedding among free-ranging felids, which are responsible for the majority of environmental contamination. We determined how climate and anthropogenic factors influence oocyst shedding in free-ranging domestic cats and wild felids using generalized linear mixed models. T. gondii oocyst shedding data from 47 studies were systematically reviewed and compiled for domestic cats and six wild felid species, encompassing 256 positives out of 9,635 total fecal samples. Shedding prevalence in domestic cats and wild felids was positively associated with human population density at the sampling location. Larger mean diurnal temperature range was associated with more shedding among domestic cats and warmer temperature in the driest quarter was associated with lower oocyst shedding in wild felids. Increasing human population density and temperature fluctuation can exacerbate environmental contamination with the protozoan parasite T. gondii. Management of free-ranging domestic cats could lower the burden of environmental oocysts due to their large population sizes and affinity with human settlements.

Causes of mortality of kiwi (Apteryx spp.) in New Zealand: a retrospective analysis of post-mortem records, 2010-2020

AIMS

To examine and assess causes of mortality of kiwi (Apteryx spp.) submitted to Massey University between 2010 and 2020 across the five recognised species according to location, age group and captivity status in New Zealand.

METHODS

Post-mortem reports were obtained from the Massey University/Te Kunenga ki Pūrehuroa School of Veterinary Science/Wildbase Pathology Register. Inclusion criteria were all species of kiwi with a date of post-mortem examination between August 2010 and August 2020. Data from each report was exported, categorised and compared using Microsoft Excel.

RESULTS

Of a total of 1,005 post-mortem reports, there were 766 North Island brown kiwi (NIBK; A. mantelli), 83 tokoeka (A. australis), 73 rowi (A. rowi), 49 great spotted kiwi (A. haastii), and 34 little spotted kiwi (A. owenii). This comprised 19 eggs/embryos, 125 neonatal, 473 juvenile, 153 subadult, and 235 adult kiwi. There were 615 kiwi from wild populations, 148 from sanctuary populations, 238 from captivity, and four from unspecified locations. The leading cause of death was trauma, affecting 322 (32.0 (95% CI = 29.2-35.0)%) kiwi including 289 (37.3 (95% CI = 26.0-31.7)%) NIBK. Nearly half of these died from predation by mustelids, with losses recorded from neonates to adults and clustered in the central to southern North Island. Predation by dogs was the second most common cause of death, killing 84 (8.4 (95% CI = 6.7-10.2)%) kiwi, of which 65.5% came from the northern districts of the North Island. Non-infectious disease killed 214 (21 (95% CI = 18.8-24.0)%) kiwi, and included developmental deformities, gastrointestinal foreign bodies and predator trap injuries. Infectious disease killed 181 (18.0 (95% CI = 15.7-20.5)%) kiwi and the proportion decreased with age, with common diagnoses including coccidiosis, bacterial septicaemia, avian malaria, and fungal respiratory disease. Starvation affected 42 (4.2 (95% CI = 3.0-5.6)%) kiwi, comprised of mainly neonatal or juvenile individuals from wild or sanctuary populations, with a higher percentage seen in tokoeka (11/83; 13.3%) compared to other species (min 0%, max 5.9%). The cause of death was undetermined in 246 (24.5 (95% CI = 21.8-27.3)%) cases, which was most often due to poor preservation of remains. This included 33/73 (46%) rowi and 32/83 (39%) tokoeka, and affected mainly birds from sanctuary and wild populations.

CONCLUSIONS

This study enhances our understanding of causes of mortality in captive, wild and sanctuary populations of all kiwi species and age groups within contemporary New Zealand.

Genetic diversity of Toxoplasma gondii isolates from birds in the world: A systematic review

Toxoplasma gondii (T. gondii) is one of the most important foodborne pathogens that infects a large number of vertebrate species and has a cosmopolitan distribution. Birds as intermediate hosts are very important in the life cycle of T. gondii and they can be a main source of infection for humans and felids, as well as other animals. Most species of birds feed from the ground and are the best indicator for soil contamination with T. gondii oocysts. Hence, T. gondii strains isolated from birds can represent different genotypes circulating in the environment and their main predators and consumers. The recent systematic review tries to represent the population structure of T. gondii in birds around the world. Six English language databases were searched from 1990 to 2020 to find the related studies and overall, 1275 isolates of T. gondii were separated from the analyzed samples in birds. The results of our study revealed that atypical genotypes were predominant (58.8%, 750 out of 1275). Types II, III, and I had less frequency with prevalence rates of 23.4%, 13.8%, and 2%, respectively. No isolates of Type I were reported from Africa. Summarizing ToxoDB genotypes circulating in birds around the world manifested that ToxoDB #2 was the most common (101/875), followed by ToxoDB #1 (80/875), and #3 (63/875). Totally, the results of our review represented the high genetic diversity of T. gondii with circulating non-clonal strains in birds from South and North America, while clonal parasites with low genetic diversity were predominant in Europe, Asia, and Africa.

Fatal toxoplasmosis in Little Penguins (Eudyptula minor) from Penguin Island, Western Australia

Routine post mortems of deceased penguins from Penguin Island, Western Australia, found that a temporal cluster of cases presented with characteristic gross and microscopic changes, namely birds in good body condition with hepatomegaly and splenomegaly, multifocal hepatic and splenic necrosis and numerous, 1–2 μm diameter protozoan parasites within the necrotic foci.

Electron microscopy identified the protozoa as belonging to the phylum Apicomplexa. Molecular investigations by PCR gave inconsistent results. PCR performed by an external laboratory identified a novel Haemoproteus spp. organism in samples from 4 of 10 cases from this group, while PCR at Murdoch University identified Toxoplasma gondii in 12 of 13 cases (including 9 of the 10 assayed at the external laboratory). Immunohistochemistry of formalin fixed tissues also identified Toxoplasma in the hepatic and splenic lesions.

The distinctive mortalities which were observed in this group of penguins are attributed to a fulminant toxoplasmosis, with a concurrent Haemoproteus infection in some cases. Though the clinical signs of infection are unknown, the gross and microscopic appearance at post mortem is sufficiently characteristic to allow a diagnosis to be made on these features. Definitive confirmation of Toxoplasma infection can be made by immunohistochemistry or PCR.

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Deaths in Little Penguins were associated with necrosis in the liver and spleen.

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The necrotic lesions contained protozoa, free and in cysts.

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The protozoa were identified as Toxoplasma by PCR and immunohistochemistry.

Prevalence of Toxoplasma gondii infection among small mammals in Tatarstan, Russian Federation

Toxoplasma gondii is a zoonotic parasite with a wide host range that includes humans, domestic animals and wild animals. Small mammals serve as intermediate hosts for T. gondii and may contribute to the persistence of this parasite in the environment. Mass mortality in wild animals and deaths in rare endemic species make the study of this parasite of growing importance. In this study, T. gondii infection prevalence was evaluated in brain tissues from 474 small mammals captured at 26 trapping points in urban and rural areas of Tatarstan, Russian Federation. Nested PCR was used to detect the T. gondii B1 gene in the samples. Overall, 40/474 samples (8.44%) showed B1 gene positivity. T. gondii infection among the wild small mammals trapped in the rural area was significantly higher as a whole than that of the urban area as a whole. Multivariate logistical regression analysis also showed that the trapping area (rural or urban) significantly contributed to T. gondii positivity. Vegetation in the trapping points, small mammal species, sex, age or distance from the trapping points to the nearest human settlements did not significantly affect T. gondii positivity in the sampled small mammals.

Dynamics and epidemiology of Toxoplasma gondii oocyst shedding in domestic and wild felids

Oocyst shedding in domestic and wild felids is a critical yet understudied topic in Toxoplasma gondii ecology and epidemiology that shapes human and animal disease burden. We synthesized published literature dating from the discovery of felids as the definitive hosts of T. gondii in the 1960s through March 2021 to examine shedding prevalence, oocyst genotypes, and risk factors for shedding. Oocyst shedding prevalence in many geographic regions exceeded the commonly accepted 1% reported for domestic cats; crude prevalence from cross-sectional field studies of domestic cat shedding ranged from 0% in Australia to 18.8% in Africa, with greater variation in reports of oocyst shedding in free-ranging, wild felids. Shedding in wild felid species has primarily been described in captive animals, with attempted detection of oocyst shedding reported in at least 31 species. Differences in lifestyle and diet play an important role in explaining shedding variation between free-ranging unowned domestic cats, owned domestic cats and wild felids. Additional risk factors for shedding include the route of infection, diet, age and immune status of the host. It is widely reported that cats only shed oocysts after initial infection with T. gondii, but experimental studies have shown that repeat oocyst shedding can occur. Factors associated with repeat shedding are common amongst free-ranging felids (domestic and wild), which are more likely to eat infected prey, be exposed to diverse T. gondii genotypes, and have coinfections with other parasites. Repeat shedding events could play a significant yet currently ignored role in shaping environmental oocyst loading with implications for human and animal exposure. Oocyst presence in the environment is closely linked to climate variables such as temperature and precipitation, so in quantifying risk of exposure, it is important to consider the burden of T. gondii oocysts that can accumulate over time in diverse environmental matrices and sites, as well as the spatial heterogeneity of free-ranging cat populations. Key directions for future research include investigating oocyst shedding in under-sampled regions, genotyping of oocysts detected in faeces and longitudinal studies of oocyst shedding in free-ranging felids.

Epidemiologic significance of Toxoplasma gondii infections in turkeys, ducks, ratites and other wild birds: 2009-2020

Toxoplasma gondii infections are common in humans and animals worldwide. Wild and domestic avian species are important in the epidemiology of T. gondii infections because felids prey on them and excrete millions of oocysts in the environment, disseminating the infection. Herbivorous birds are also excellent sentinels of environmental contamination with T. gondii oocysts because they feed on the ground. Toxoplasma gondii infections in birds of prey reflect infections in intermediate hosts. Humans can become infected by consuming undercooked avian tissues. Here, the authors reviewed prevalence, persistence of infection, clinical disease, epidemiology and genetic diversity of T. gondii strains isolated from turkeys, geese, ducks, ratites and avian species (excluding chickens) worldwide 2009-2020. Genetic diversity of 102 T. gondii DNA samples isolated worldwide is discussed. The role of migratory birds in dissemination of T. gondii infection is discussed.

Nematode larva migrans caused by Toxocara cati in the North Island brown kiwi (Apteryx mantelli)

Sporadic cases of visceral and neural nematode larva migrans have been diagnosed at necropsy in the endangered New Zealand kiwi (Apteryx spp.), but the causative organisms have not yet been definitively identified. From an initial group of five affected kiwi, PCR was performed on DNA extracted from archival formalin-fixed paraffin-embedded tissue sections in which larval nematodes had been histologically identified. Sequencing of positive results from four out of the five kiwi aligned with sequences from Toxocara cati, a nematode parasite whose definitive host is the domestic cat. PCR was then performed on a second group of 12 kiwi that had histologic inflammatory lesions consistent with larva migrans, but variable larval presence. Repeatable positive PCR results were only achieved in one tissue, in which larval organisms were histologically confirmed. This study supports the use of PCR as an alternative or adjunct to the morphological identification of nematode larvae in formalin-fixed histopathological samples, as well as showing that in investigation of larva migrans, PCR has greatest chance of success from sections where nematode larvae are evident histologically. The identification of Toxocara cati from lesions of larva migrans in kiwi reflects an indirect, parasite-mediated effect of an invasive mammalian species on a native species.

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Cases of nematode larva migrans have been diagnosed in the New Zealand kiwi.

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PCR was performed on archival formalin-fixed paraffin-embedded tissue blocks.

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Results identified Toxocara cati, a parasite of cats, as the causative agent.

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PCR had greatest success from tissues where larvae were identifiable histologically.

Comparison of PCR assays to detect Toxoplasma gondii oocysts in green-lipped mussels (Perna canaliculus)

Toxoplasma gondii is recognised as an important pathogen in the marine environment, with oocysts carried to coastal waters in overland runoff. Currently, there are no standardised methods to detect T. gondii directly in seawater to assess the extent of marine ecosystem contamination, but filter-feeding shellfish may serve as biosentinels. A variety of PCR-based methods have been used to confirm presence of T. gondii DNA in marine shellfish; however, systematic investigations comparing molecular methods are scarce. The primary objective of this study was to evaluate analytical sensitivity and specificity of two nested-PCR (nPCR) assays targeting dhps and B1 genes and two real-time (qPCR) assays targeting the B1 gene and a 529-bp repetitive element (rep529), for detection of T. gondii. These assays were subsequently validated for T. gondii detection in green-lipped mussel (Perna canaliculus) haemolymph using oocyst spiking experiments. All assays could reliably detect 50 oocysts spiked into mussel haemolymph. The lowest limit of detection was 5 oocysts using qPCR assays, with the rep529 primers performing best, with good correlation between oocyst concentrations and Cq values, and acceptable efficiency. Assay specificity was evaluated by testing DNA from closely related protozoans, Hammondia hammondi, Neospora caninum, and Sarcocystis spp. Both nPCR assays were specific to T. gondii. Both qPCR assays cross-reacted with Sarcocystis spp. DNA, and the rep529 primers also cross-reacted with N. caninum DNA. These studies suggest that the rep529 qPCR assay may be preferable for future mussel studies, but direct sequencing is required for definitive confirmation of T. gondii DNA detection.

Investigation of Toxoplasma gondii and association with early pregnancy and abortion rates in New Zealand farmed red deer (Cervus elaphus)

This study tested for association between Toxoplasma gondii and pregnancy and abortion to investigate sub-optimal reproduction in farmed red deer (Cervus elaphus). Sera from a sub-sample (n = 2304) of pregnant and non-pregnant hinds in early gestation at first pregnancy scan (scan 1) and approximately at the end of second trimester at second pregnancy scan (scan 2) were tested for T. gondii antibodies using a validated ELISA. Foetuses and/or uteri from pregnant, non-pregnant, and aborting hinds at scan 1, scan 2, or weaning were tested for T. gondii DNA by nested PCR. At scan 1, 31.1% of 861 rising two-year-old (R2) and 28.3% of 357 mixed-aged (MA, ≥ 2 years) hinds were sero-positive. There was no association between scan 1 serology and non-pregnancy at animal (R2, p = 0.05 and MA, p = 0.43) or herd level (R2, p = 0.37). Toxoplasma gondii DNA was detected in 3/18 placenta and 4/18 foetal brains from aborting R2 hinds and 15/157 R2 and 3/21 MA uteri from non-pregnant hinds at scan 1. At scan 2, sero-prevalence was higher (odds ratio = 1.6, 95% CI = 1.04-2.48) in aborted (34.3% of 268) than in non-aborted (23.5% of 446) R2 hinds (p = 0.03) and 7.9% of abortions between scans were attributable to T. gondii exposure. Within-herd sero-prevalence at scan 2 was positively associated with daily abortion rate in R2 herds with aborted hinds (p < 0.001) but not in MA herds (p = 0.07). Toxoplasma gondii DNA was detected in 27/169 uteri, 2/20 cotyledons, and 1/5 foetal brains from aborted hinds at scan 2 and in uteri from 5/33 hinds not rearing a calf to weaning. Toxoplasma gondii RFLP genotyping of five loci revealed a unique type I/III genotype pattern, TgRDNZ1, in a foetal brain sample, not been previously reported in deer. These findings provide serological and molecular evidence that T. gondii infection is associated with abortion in red deer, possibly in all three trimesters.

Prevalence of toxoplasmosis and genetic characterization of Toxoplasma gondii strains isolated in wild birds of prey and their relation with previously isolated strains from Turkey

Toxoplasma gondii is a protozoon parasite that causes congenital toxoplasmosis, as well as other serious clinical presentations, in immune compromised humans. Analyses of the prevalence and genotyping of strains from the definitive host and intermediate hosts will help to understanding the circulation of the different strains and elucidating the role of the genotype(s) in human toxoplasmosis. Turkey has a specific geographic location bridging Africa, Europe, and Asia. We hypothesized that T. gondii strains may have been transferred to Turkey from these continents via migratory birds or vice versa. The present study aimed to assess the prevalence of toxoplasmosis in wild birds of prey of İzmir and Manisa provinces as well as genetically characterize T. gondii strains from these wild birds to show the relation between bird strains and neighboring stray cats as well as human strains previously isolated in Turkey. Tissues obtained from 48 wild birds were investigated for the presence of T. gondii DNA and then bioassayed in mouse. Isolated strains were genotyped using 15 microsatellite markers. The prevalence of T. gondii DNA was found to be 89.6% (n: 43/48) in wild birds. Out of 43 positive samples, a total of 14 strains were genotyped by 15 microsatellite markers. Among them, eight were type II, three were type III and three were mixture of genotypes (two type II/II and one was II/III). These are the first data that showed the presence of T. gondii and types II and III genotypes in wild birds of Turkey. Moreover, Africa 1 was not detected. In addition, cluster analysis showed that T. gondii strains within type II and III lineage have close relation with strains previously isolated from stray cats in İzmir. Further studies are required to isolate more strains from human cases, other intermediate hosts, and water sources to reveal this relation.

A retrospective survey into the presence of Plasmodium spp. and Toxoplasma gondii in archived tissue samples from New Zealand raptors: New Zealand falcons (Falco novaeseelandiae), Australasian harriers (Circus approximans) and moreporks (Ninox novaeseelandiae)

Human colonisation of New Zealand has resulted in the introduction of emerging diseases, such as avian malaria and toxoplasmosis, which arrived with their exotic avian and mammalian hosts. Plasmodium spp. and Toxoplasma gondii have a wide host range, and several species of endemic New Zealand birds have developed a fatal disease following infection with either pathogen. However, no reports of either toxoplasmosis or avian malaria in New Zealand raptors, namely, the New Zealand falcons (Falco novaeseelandiae), Australasian harriers (Circus approximans) and moreporks (Ninox novaeseelandiae) exist in the literature. Therefore, this study was designed to determine if these two pathogens are present in these raptors through a retrospective analysis of archived tissue samples. Detection and isolate identification of these pathogens was determined using established histological and molecular techniques. All three species of New Zealand raptors tested positive for the presence of Plasmodium spp. (10/117; 8.5%) and an atypical genotype of T. gondii (9/117; 7.7%). Plasmodium lineages identified include P. elongatum GRW6, P. relictum SGS1, P. relictum PADOM02 and Plasmodium sp. LINN1. Two Australasian harriers and one morepork tested positive for the presence of both Plasmodium spp. and T. gondii. However, the pathogenicity of these organisms to the raptors is unclear as none of the tissues showed histological evidence of clinical disease associated with Plasmodium spp. and T. gondii infections. Thus, these results demonstrate for the first time that these two potential pathogens are present in New Zealand's raptors; however, further research is required to determine the prevalence and pathogenicity of these organisms among the living populations of these birds in the country.

Infectious Diseases

The chapter describes bacerial, viral, parasitic and fungal infections commonly detected in pet birds. The chapter includes history, etiology, susceptible hosts, transmission, pathogenesis, clinical symptoms, lesion, diagnosis, zoonosis, Treatment and control strategy of Tuberculosis, Salmonellosis, Chlamydiosis, Campylobacteriosis, Lyme disease, other bacterial infection, Newcastle disease, Avian Influenza infection, West Nile Virus infection, Usutu virus infection, Avian Borna Virus infection, Beak and feather disease, other viral infection, Toxoplasmosis, Giardiasis, Cryptosporidiosis, other parasitic infection, Cryptococcosis, Aspergillosis, Other fungal infections.

Diagnosing species decline: a contextual review of threats,causes and future directions for management and conservation of the eastern quoll

Diagnosing the cause of a species’ decline is one of the most challenging tasks faced by conservation practitioners. For a species approaching extinction, it is not possible to go back in time to measure the agents that operated at various stages of the decline. Accordingly, managers are often restricted to measuring factors currently affecting residual populations, which may not be related to factors that operated earlier in the decline, and inferring other mechanisms from different lines of evidence. In this review, I adopt a methodical diagnostic framework to comprehensively evaluate the potential causal factors for the decline of the eastern quoll (Dasyurus viverrinus) in Tasmania, and propose a hypothesis as to the cause of decline. Potential causal agents were gleaned from two key sources: factors implicated in the eastern quoll’s historical demise on the Australian mainland, and factors that changed during the recent period of quoll decline in Tasmania. The three most likely candidate causal agents were investigated over 4 years to evaluate their likely contribution to the decline. Here, I synthesise the findings from this recent research to advance a hypothesis as to the cause of the eastern quoll decline in Tasmania. I suggest that a period of unsuitable weather reduced quoll populations to an unprecedented low abundance, and that populations are now too small to overcome established threat intensities to which they were robust when at higher densities. Residual small populations are inherently more susceptible to demographic, environmental and genetic stochasticity and are unlikely to recover without management intervention. I propose a study design to experimentally test this hypothesis, and outline priority areas for future research and actions to guide in the future management and conservation of the species. This case study illustrates an approach by which practical species conservation problems might be solved and recovery strategies may be better informed, thereby ensuring positive conservation outcomes for threatened species.

Toxoplasmosis in a Pet Peach-Faced Lovebird (Agapornis roseicollis)

Toxoplasma gondii atypical type II genotype was diagnosed in a pet peach-faced lovebird (Agapornis roseicollis) based on histopathology, immunohistochemistry, and multilocus DNA typing. The bird presented with severe neurological signs, and hematology was suggestive of chronic granulomatous disease. Gross post-mortem examination revealed cerebral hemorrhage, splenomegaly, hepatitis, and thickening of the right ventricular free wall. Histologic sections of the most significant lesions in the brain revealed intralesional protozoan organisms associated with malacia, spongiform changes, and a mild histiocytic response, indicative of diffuse, non-suppurative encephalitis. Immunohistochemistry confirmed the causative organisms to be T. gondii. DNA isolated from the brain was used to confirm the presence of T. gondii DNA. Multilocus genotyping based on SAG1, altSAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and Apico markers demonstrated the presence of ToxoDB PCR-RFLP genotype #3 and B1 gene as atypical T. gondii type II. The atypical type II strain has been previously documented in Australian wildlife, indicating an environmental transmission route.

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.