Toxoplasma gondii is a notoriously widespread parasite found in much of the world, with nearly a third of humankind being predicted to be exposed to the parasite. In Europe and the United States alone, it is predicted that around 50-80% and 9-40% of people, respectively, are infected with T. gondii.

The protozoal parasite can be transmitted from the mother to the baby both faecal-orally and through ingestion of contaminated meat products or by crossing the placental barrier.

Although virtually all warm-blooded animals can host T. gondii In the event of an infection, only infected cats act as final hosts – this means that sexual reproduction (production of oocysts) and transmission via the fecal-oral route can only occur if a cat is involved in the life cycle. However, the life cycle can be increased by the consumption of raw / undercooked meat T. gondii Cysts in the tissues and is the most common way that toxoplasmosis occurs in humans.

As meat consumption is expected to increase in the next generations (due to increasing population size) and as we continue to penetrate wildlife habitats to expand our farms and cities, the incidence and recurrence of zoonotic diseases such as T. gondii an increase is also expected in humans.

The vast majority of infections are asymptomatic and pose no real threat to human health. However, this does not apply to those with compromised immune systems or those who have recently been pregnant and who are more likely to have severe symptoms and neurological complications.

It has been proven that over 50% of human pathogens are of zoonotic origin and originate from wildlife pathogens.

Therefore, accurate and detailed monitoring of T. gondii and other zoonotic diseases affecting humans will also be of increasing need as the rapid detection of emerging / reoccurring infectious diseases will be one of the best defensive measures to protect human health.

Toxoplasma gondii life cycle, edited to include marsupials. Sources: Original CDC life cycle (public domain). Eastern gray giant kangaroo (CC BY-NC – Fir0002 / Flagstaffotos). Red-necked Wallaby (CC BY-SA 4.0 – Grendelkhan).

In a recent article by Jitender Dudey and colleagues, decades of research into the epidemiology, genetic diversity, and clinical disease manifestations of T. gondii in Australian marsupials.

The study summarizes this research on wild marsupials in Australia as well as those in zoos around the world and includes marsupials such as koalas, wallabies, kangaroos, wombats and quolls.

Free-living (wild) marsupials vs. captured marsupials

It has been known for decades that Toxoplasma can cause serious illness and death in marsupials. Most wild marsupials, however, develop chronic infections with no clinical signs, a departure from their captive counterparts, which appear very susceptible to clinical toxoplasmosis.

It has been suggested that the different genotypes of T. gondii found in the wild vs. Captive marsupials can support this trend, as most deaths in captivity are due to disseminated toxoplasmosis (cysts that spread throughout the body and often infect multiple organs, including brain tissue).

Genetic diversity

Differences in genotypes of T. gondii between wild and captive marsupials have been identified that reflect the diversity of globally circulating genotypes and may help reduce the differences in disease severity between wild and captive marsupials on the to explain all over the world. The authors note that the degree of cross-fertilization and recombination between the genotypes of T. gondii in wild marsupial populations is of particular concern as these processes would further increase the genetic diversity of parasites circulating in the wild and increase the chance for new, highly virulent genotypes to form.

Koalas (Phascolarctos cinereus)

A study of the seroprevalence of T. gondii in South Australian koalas there was a clear lack of antibodies against T. gondii. The authors suggested that this could be due to the koalas’ herbivorous and tree-dwelling lifestyle, which reduced their likelihood of exposure to oocysts in cat feces.

Wombats (Vombatus ursinus), Wallabies (Petrogale penicillata) & Quoll.

The assumption that koalas are at negligible risk of infection due to their way of life and their habitat is supported in the investigation of toxoplasmosis infection in ground-dwelling marsupials such as wombats and wallabies. One study found that 4.6% of wallabies in Queensland and 8% from Tasmania were positive for antibodies against. were T. gondii. Eight wombats living in the wild that died in the wild have all been post-mortally diagnosed with fatal toxoplasmosis. In the quolls in one study, an astonishing 71% of the spotted-tails and 58% of the eastern quolls were positive, while in another study 5-100% of the 290 quolls sampled from four locations were seropositive. The prevalence rates were found to be directly related to the presence of wild cats in the area.

Kangaroos

Similar research by T. gondii Infections in the wild western gray giant kangaroo (Macropus ocydomus) from seven and four locations in the Perth area found that 34/219 (15.5%) and 20/102 (19.7%) were positive for infection, respectively. In addition to environmental ingestion, fatal toxoplasmosis has also previously been observed in two young, pouch-bound boys, suggesting the occurrence of vertical transplacental transmission of. approved T. gondii in marsupials.

Possible public health consequences

The high prevalence of T. gondii Infection in most Australian marsupials, especially kangaroos, is of particular public health concern. In 2011, the Australian government estimates that 34.3 million kangaroos live in Australia’s commercial harvesting areas, with wild-caught kangaroo meat being exported to over 60 markets around the world.

By T. gondiiAs one of the most common parasites of humans and animals worldwide, the consumption of raw or undercooked infected meat can be a source of infection for humans worldwide – especially since the consumption of kangaroo meat by humans is increasing.

Therefore, close monitoring of toxoplasmosis from wildlife populations such as marsupials is essential if we are to prevent future outbreaks before they occur.

Kangaroo meat consumption (kg per capita) in Australia. Source: Ratnasiri & Bandara, 2017

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