Clinical and pathological features of toxoplasmosis in free-ranging common wombats (Vombatus ursinus) with multilocus genotyping of Toxoplasma gondii type II-like strains

Prevalence of Toxoplasmic Retinochoroiditis in an Australian Adult Population: a Community-Based Study

OBJECTIVE

Toxoplasmic retinochoroiditis is the most common clinical manifestation of an infection with the protozoan parasite, Toxoplasma gondii. Up to 50% of the human population is estimated to be infected with T. gondii. However, the epidemiology of toxoplasmic retinochoroiditis is not widely reported. We sought to estimate the prevalence of toxoplasmic retinochoroiditis in Australia using data collected as part of the Busselton Healthy Ageing Study.

DESIGN

Cross-sectional, community-based, prospective cohort study.

PARTICIPANTS

5,020 Australian adults (2,264 men and 2,756 women; age range of 45-69 years and median age of 58 years).

METHODS

Retinal color photographs centered on the optic disc and macula were captured on a digital retinal camera following dilation of the pupils. Three uveitis-subspecialized ophthalmologists assessed each pigmented retinal lesion, and complete concordance of opinion was required to assign a toxoplasmic etiology. Serum T. gondii immunoglobulin (Ig)G levels were measured for those participants with retinal lesions judged to be toxoplasmic retinochoroiditis.

MAIN OUTCOME MEASURES

Prevalence of toxoplasmic retinochoroiditis.

RESULTS

Eight participants (0.16%) had retinal lesions that were considered to have the characteristic appearance of toxoplasmic retinochoroiditis, plus detectable serum T. gondii IgG, consistent with the diagnosis of toxoplasmic retinochoroiditis. On the assumption that 23.81% of retinal lesions occur at the posterior pole, as reported in a community-based survey conducted in Brazil (Sci Rep. 2021;11:3420), the prevalence of toxoplasmic retinochoroiditis was estimated at 0.67% or 1 per 149 persons.

CONCLUSIONS

Toxoplasmic retinochoroiditis is common in Australian adults. Efforts to quantify and address risk factors for human infection with T. gondii are justified.

Recent aspects on epidemiology, clinical disease, and genetic diversity of Toxoplasma gondii infections in Australasian marsupials

Background

Toxoplasma gondii infections are common in humans and animals worldwide. Among all intermediate hosts of T. gondii, captive marsupials from Australia and New Zealand are highly susceptible to clinical toxoplasmosis. However, most free-range marsupials establish chronic T. gondii infection. Infected marsupial meat may serve as a source of T. gondii infection for humans. Differences in mortality patterns in different species of kangaroos and other marsupials are not fully understood. Lifestyle, habitat, and the genotype of T. gondii are predicted to be risk factors. For example, koalas are rarely exposed to T. gondii because they live on treetops whereas wallabies on land are frequently exposed to infection.

Methods

The present review summarizes worldwide information on the prevalence of clinical and subclinical infections, epidemiology, and genetic diversity of T. gondii infecting Australasian marsupials in their native habitat and among exported animals over the past decade. The role of genetic types of T. gondii and clinical disease is discussed.

Results

Fatal toxoplasmosis has been diagnosed in captive Australasian marsupials in Argentina, Chile, China, Germany, Hungary, Japan, Spain, Turkey, and the USA. Most deaths occurred because of disseminated toxoplasmosis. Genetic characterization of T. gondii strains isolated from fatal marsupial infections identified Type III as well as atypical, nonclonal genotypes. Fatal toxoplasmosis was also diagnosed in free-ranging wombats (Vombatus ursinus) in Australia. Genetic characterization of DNA amplified directly from host tissues of subclinical culled kangaroos at slaughter identified many mixed-strain infections with both atypical and recombinant genotypes of T. gondii.

Conclusions

Most Australasian marsupials in their native land, Australia and New Zealand, have high prevalence of T. gondii, and kangaroo meat can be a source of infection for humans if consumed uncooked/undercooked. The genotypes prevalent in kangaroos in Australia and New Zealand were genetically distinct from those isolated or genotyped from most macropods in the USA and other countries. Thus, clinical toxoplasmosis in marsupials imported from Australia is most likely to occur from infections acquired after importation.

Graphic abstract

Parasites of wombats (family Vombatidae), with a focus on ticks and tick-borne pathogens

Ticks (Arachnida: Acari) are vectors for pathogens and the biggest threat to animal health. Many Australian ticks are associated with pathogens that impact humans, domestic animals and livestock. However, little is known about the presence or impact of tick-borne pathogens in native Australian wildlife. Wombats are particularly susceptible to the effects of the ectoparasite Sarcoptes scabiei which causes sarcoptic mange, the reason for which is unknown. Factors such as other ectoparasites and their associated pathogens may play a role. A critical understanding of the species of ectoparasites that parasitise wombats and their pathogens, and particularly ticks, is therefore warranted. This review describes the ectoparasites of wombats, pathogens known to be associated with those ectoparasites, and related literature gaps. Pathogens have been isolated in most tick species that typically feed on wombats; however, there are minimal molecular studies to determine the presence of pathogens in any other wombat ectoparasites. The development of next-generation sequencing (NGS) technologies allows us to explore entire microbial communities in ectoparasite samples, allowing fast and accurate identification of potential pathogens in many samples at once. These new techniques have highlighted the diversity and uniqueness of native ticks and their microbiomes, including pathogens of potential medical and veterinary importance. An increased understanding of all ectoparasites that parasitise wombats, and their associated pathogens, requires further investigation.

A review of wombat diet and nutrition

In this review we investigated the diet and nutrition of wombats and highlight areas for future research. The low energy requirements of wombats, conservative foraging behaviours and burrowing lifestyle allow them to subsist on low-quality food. Furthermore, their digestive anatomy and physiology is well adapted for digesting the resources available in their habitats. All species feed predominantly on native grasses; however, the nutritional requirements of juvenile and aged wombats are largely unknown. Changes to food availability and grass species in wombat habitats may alter their diet and nutritional intake. Also, despite evidence suggesting that wombats can satisfy their water requirements via the food they eat, the minimum threshold of water content at which wombats will cease feeding is unknown. Other areas for future research include investigating factors that affect digesta retention times (such as age or lactation), and the development of a method to determine age, because unlike most other mammals, wombat teeth grow continuously, hence teeth cannot be used as a reliable predictor of age in wombats.

Chlamydia pecorum-Associated Sporadic Ovine Abortion

Despite previous detection of Chlamydia pecorum in sporadic ovine abortions, published descriptions of naturally occurring infections with fetoplacental lesions are lacking. This report provides the first descriptions of severe necrosuppurative chorionitis with vasculitis, and fetal pyelonephritis and enteritis in late-term abortions of maiden ewes. Chlamydial infection was detected using a Chlamydia genus-specific qPCR (quantitative polymerase chain reaction) on tissue extracts from 3 fetuses. C. pecorum was identified using a targeted qPCR assay, which also determined infectious load within fetal tissues. The presence of viable C. pecorum in fetal samples was confirmed by cell culture. Multilocus sequence typing (MLST) data indicated that the C. pecorum strains from each fetus were identical and of sequence type (ST) 23. Chlamydia sp. immunohistochemistry showed strong positive immunolabeling of fetoplacental lesions. Other infectious abortigenic agents were excluded with specific testing. This report confirms C. pecorum as a likely cause of ovine abortion and provides the first descriptions of associated fetoplacental lesions in naturally infected sheep.

Disseminated protozoal infection in a wild feathertail glider (Acrobates pygmaeus) in Australia

This is the first report of a disseminated protozoal infection in a wild feathertail glider (Acrobates pygmaeus) from south-eastern Australia. The glider was found dead in poor body condition. Histologically, large numbers of zoites were seen predominantly in macrophages in the liver, spleen and lung, with protozoal cysts present in the liver. Molecular and phylogenetic analyses inferred that the protozoan parasite belongs to the family Sarcocystidae and is closely related to previously identified apicomplexans found in yellow-bellied gliders (Petaurus australis) in Australia and southern mouse opossums (Thylamys elegans) in Chile.

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A novel apicomplexan parasite caused a disseminated fatal disease in a wild feathertail glider.

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The apicomplexan parasite is a member of the family Sarcocystidae.

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It is most closely related to parasites previously identified in yellow-bellied gliders in Australia and southern mouseopossums in Chile.

BASELINE HEALTH AND DISEASE ASSESSMENT OF FOUNDER EASTERN QUOLLS (DASYURUS VIVERRINUS) DURING A CONSERVATION TRANSLOCATION TO MAINLAND AUSTRALIA

We evaluated the health of 31 (eight males, 23 females) founder eastern quolls (Dasyurus viverrinus), translocated to a fenced reserve in the Australian Capital Territory between February 2016 and July 2017. Quolls were wild caught in Tasmania (16 animals) or captive bred at Mount Rothwell Biodiversity Interpretation Centre, Victoria (15 animals). Quolls were assessed for the presence of selected potential pathogens (Toxoplasma gondii, herpesviruses, Salmonella serovars, hemoprotozoa, and ectoparasites). We assessed the relationships among sex, provenance (captive or free ranging), T. gondii or herpesvirus infection, weight, and hematologic and biochemical variables. Six of 21 quolls (29%) tested were seropositive for antibodies to T. gondii. Seropositive quolls weighed significantly more and had significantly lower potassium levels, anion gaps, and urea and triglyceride levels than seronegative quolls had. Eighteen of 31 (58%) combined conjunctival-pharyngeal-cloacal swabs collected from quolls were PCR positive for a newly identified gammaherpesvirus, tentatively named dasyurid gammaherpesvirus 3. There were no significant differences among hematologic and biochemical variables or body weights from PCR-positive and PCR-negative quolls. Eighteen of 18 (100%) of rectal-swab samples were culture negative for Salmonella serovars. Three species of tick (Ixodes tasmani, Ixodes fecialis, and Ixodes holocyclus), two species of mite (Andreacus radfordi, one unidentified), and four species of flea (Pygiopsylla hoplia, Acanthopsylla rothschildi rothschildi, Uropsylla tasmanica, and Stephanocircus dasyuri), were detected on wild-caught quolls, whereas a fifth species of flea, Echidnophaga myremecobii, was detected only on captive-bred quolls. Five of 15 blood samples (33%) were positive for hemoprotozoan DNA via PCR, a novel Hepatozoon species, a novel Theileria species, Theileria paparinii, and Trypanosoma copemani were detected. Despite the presence of several potential pathogens known to be associated with disease in other marsupials, the quolls were considered to be in good general health, suitable for translocation, and a viable population was subsequently established.

Distribution, abundance and threats to bare-nosed wombats (Vombatus ursinus)

Wombats are large marsupial grazers native to Australia. They are ‘ecosystem engineers’ due to their burrowing, impacting rates of soil turnover, assisting with nutrient cycling and water infiltration, and creating habitat for other species. The aim of this review is to provide an overview of available information on the habitat and distribution, abundance and threats to bare-nosed wombats (Vombatus ursinus), and to provide a critical review of the current gaps in our knowledge to aid future management of the species. Bare-nosed wombats were previously widespread. Since European settlement their range has reduced. While habitat loss and contraction impact population numbers, bare-nosed wombat populations are also threatened by roadkill, introduced species, legal and illegal human persecution, and disease. Further research is required to understand the historic range of bare-nosed wombats, as well as current population numbers, so that we can determine the threats that most significantly impact this species. Increasing our understanding of habitat requirements, distribution and population numbers, as well as how to mitigate threats, will aid future management and conservation strategies for the species.

Wildlife parasitology in Australia: past, present and future

Wildlife parasitology is a highly diverse area of research encompassing many fields including taxonomy, ecology, pathology and epidemiology, and with participants from extremely disparate scientific fields. In addition, the organisms studied are highly dissimilar, ranging from platyhelminths, nematodes and acanthocephalans to insects, arachnids, crustaceans and protists. This review of the parasites of wildlife in Australia highlights the advances made to date, focussing on the work, interests and major findings of researchers over the years and identifies current significant gaps that exist in our understanding. The review is divided into three sections covering protist, helminth and arthropod parasites. The challenge to document the diversity of parasites in Australia continues at a traditional level but the advent of molecular methods has heightened the significance of this issue. Modern methods are providing an avenue for major advances in documenting and restructuring the phylogeny of protistan parasites in particular, while facilitating the recognition of species complexes in helminth taxa previously defined by traditional morphological methods. The life cycles, ecology and general biology of most parasites of wildlife in Australia are extremely poorly understood. While the phylogenetic origins of the Australian vertebrate fauna are complex, so too are the likely origins of their parasites, which do not necessarily mirror those of their hosts. This aspect of parasite evolution is a continuing area for research in the case of helminths, but remains to be addressed for many other parasitic groups.

Sarcoptic mange in wombats-A review and future research directions

Sarcoptic mange is caused by the mite Sarcoptes scabiei and has recently been recognized as an emerging infectious disease of wildlife worldwide. The mite is one of the main causes of population decline in southern hairy-nosed (Lasiorhinus latifrons) and bare-nosed wombats (Vombatus ursinus). This review focuses on Sarcoptes scabiei infestations in wombats and provides insights into why the disease may be so prevalent in wombats. Current treatment practices and trials conducted in the field to reduce the incidence of sarcoptic mange in wombats are described and critically reviewed. Current and potential future avenues of research are discussed.

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.

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.

The utility of diversity profiling using Illumina 18S rRNA gene amplicon deep sequencing to detect and discriminate Toxoplasma gondii among the cyst-forming coccidia

Next-generation sequencing (NGS) has the capacity to screen a single DNA sample and detect pathogen DNA from thousands of host DNA sequence reads, making it a versatile and informative tool for investigation of pathogens in diseased animals. The technique is effective and labor saving in the initial identification of pathogens, and will complement conventional diagnostic tests to associate the candidate pathogen with a disease process. In this report, we investigated the utility of the diversity profiling NGS approach using Illumina small subunit ribosomal RNA (18S rRNA) gene amplicon deep sequencing to detect Toxoplasma gondii in previously confirmed cases of toxoplasmosis. We then tested the diagnostic approach with species-specific PCR genotyping, histopathology and immunohistochemistry of toxoplasmosis in a Risso's dolphin (Grampus griseus) to systematically characterise the disease and associate causality. We show that the Euk7A/Euk570R primer set targeting the V1-V3 hypervariable region of the 18S rRNA gene can be used as a species-specific assay for cyst-forming coccidia and discriminate T. gondii. Overall, the approach is cost-effective and improves diagnostic decision support by narrowing the differential diagnosis list with more certainty than was previously possible. Furthermore, it supplements the limitations of cryptic protozoan morphology and surpasses the need for species-specific PCR primer combinations.