It seems that hunting is not the only way that feral cat activity is taking out our wildlife.

Toxoplasma gondii, a parasite commonly found in cat faeces, is a well-known threat to human health, but less people realise that it also causes disease and death in native animals and livestock.

The protozoa Toxoplasma gondii is a single-celled parasite which can live in (and be passed on from) many types of animals. In order for it to mature and breed it must pass through a cat’s digestive system – hence its association with cats and their faeces – with cats being the ‘definitive host’. Adult parasites shed their eggs in the cat faeces, which can be picked up if an animal or person accidentally swallows soil or plant material contaminated with the droppings. At this point, the animal or person is the ‘intermediate host’ and the parasite develops to the next stage, invading tissues and forming cysts and often causing serious problems like encephalitis, blindness, miscarriage or stillbirth. In any animal other than a cat, the parasite won’t produce eggs and nothing is spread in the droppings, but if an infected animal is caught and eaten, the protozoa in the meat will be passed to the predator. If the predator is in fact a cat, then the cycle will start again.

Toxoplasmosis (illness caused by T. gondii) has been associated with signs of neurological disorder and intoxication in livestock, abortion in sheep, and a reduction in meat value. The effects on native wildlife vary and are not fully understood, but are often severe and fatal. Wallabies are known to develop blindness, diarrhoea, neurological symptoms and an inability to eat or drink, while bandicoots often suffer progressive paralysis and death. Possums, numbats, quolls and bilbies can all become infected too, however Western Grey Kangaroos don’t appear to be impacted by the parasite (although subtle symptoms may not yet be recognised). Many native birds can also acquire toxoplasmosis, becoming debilitated, lethargic and vulnerable to predators as the parasite invades the lungs, brain and other organs.

It’s believed the parasite may even manipulate the way the infected animal thinks. Studies have shown it can cause intermediate hosts to lose their fear of predators, or even be attracted to them! This effect, which is thought to be caused by the parasite altering hormone levels in the carrier, means that the ultimate feline host is more likely to catch its next meal, and the parasite will be able to complete its life cycle and breed all over again.

It is important to note that humans can also be infected by Toxoplasma gondii. Those who are infected may feel as if they have the flu, or may not feel sick at all. Others, (especially the immune-compromised, elderly, or very young), may develop severe illness or mental illness, and can end up with impaired vision or brain function. Infection amongst pregnant women is perhaps the most dangerous, potentially leading to miscarriage or still-birth. Humans can reduce their risk of picking up the parasite by always washing hands after working or playing in soil, washing any vegetables or fruit before eating, cooking meat well, and taking care when emptying pet cat litter trays.

Cats themselves don’t show any signs of Toxoplasma gondii infection, so you aren’t able to tell when they may be carrying it and spreading it around. For the sake of both wildlife and livestock then, it is even more important to keep domestic cats away from bushland and paddocks so they don’t pass parasite eggs into the environment through their faeces. Keeping pet cats indoors (or in special active cat enclosures) and reducing numbers of feral cats in the local area, can improve chances for both native animal populations and livestock production, and help keep our community healthy.