What is toxoplasmosis?

Toxoplasmosis is a disease that can be transmitted from animals to humans (zoonosis). It is caused by the parasite Toxoplasma gondii (T. gondii), which can infect any warm-blooded animal.

What is T. gondii?

T. gondii must pass through cats to complete its life cycle (they are the definitive host, or where the parasite reaches maturity and reproduces). Cats do not usually show any signs of illness associated with T. gondii. When a cat eats an animal infected with T. gondii, the parasite multiplies in the cat and produces infective cysts (oocysts), which are shed in the cat’s faeces for around 10 to 14 days. After this time most cats will not continue to shed oocysts in their faeces.

Oocysts that have been shed in cat faeces are not immediately infectious to other animals. They must first go through a process called sporulation, which takes 1 to 5 days depending on conditions. Oocysts are very hardy and may survive in the environment for over a year; potentially even longer in conditions created by climate change.

Other animals, including humans, can become infected with T. gondii but the parasite does not produce oocysts (intermediate hosts). Intermediate hosts become infected by ingesting sporulated oocysts, and tissue cysts form in various parts of the body. Cats, humans, and other animals can become infected if they eat cyst-containing tissue.

How are humans infected with T. gondii?

Humans are most commonly exposed to T. gondii by eating raw or undercooked meat containing tissue cysts. It is also possible for infection to occur via the consumption of water, unwashed vegetables, unpasteurised milk, and soil contaminated with oocysts, and via organ donation or blood transfusion. Babies can be infected in the womb or after birth.

How common is toxoplasmosis in humans?

It is estimated that nearly a third of the global human population has been exposed to T. gondii. However, serious cases of toxoplasmosis are rare, usually only occurring in individuals who have a compromised immune system (e.g., immunodeficiency virus, organ transplant, cancer treatment, pregnant women, babies).

Can I “catch” toxoplasmosis from my cat?

Owning a cat does not mean you will be exposed to T. gondii or develop toxoplasmosis. Direct contact with a cat is generally not considered to be a primary risk factor for human infection with T. gondii. Although cats are part of the life cycle of T. gondii, people usually become infected through ingestion of oocyst-contaminated soil and water and tissue cysts in undercooked or raw meat, and infection almost always occurs without the knowledge of the patient.

Even if a cat becomes infected, they generally will only shed the organism for a short period (around two weeks after they are first infected by the parasite) in their entire life. So, the chance of human exposure is very small. Simple precautions can reduce that risk even further.

What precautions can I take to reduce the risk of toxoplasmosis?

Speak to your veterinarian if you have any questions or need more information about toxoplasmosis. The following is general information only and you are advised to speak to your veterinarian and medical doctor for advice specific to your individual circumstances.

• Food preparation – Avoid eating eat raw or undercooked meat, freeze meat at -12°C for at least 24 hours before preparing and eating it, and do not drink unpasteurised milk, unpasteurised dairy products, or untreated water. Wash all fruit and vegetables before eating.
• Hygiene – Wash hands before eating, after handling raw meat, and after coming into contact with soil/sand/cat litter. Disinfect surfaces and kitchen implements after preparing raw meat.
• Personal protective equipment – Wear gloves when gardening or during any activity involving contact with soil.
• Prevent exposure of your cat to T. gondii via intermediate hosts (e.g., rodents, birds, and other animals) and vectors (i.e., potential physical carriers of T. gondii such as cockroaches). This includes avoiding feeding raw meat to your cats and taking effective steps to stop your cat hunting and eating prey (to prevent them eating tissue cysts containing T. gondii). Keeping your cat at home on your property can reduce their exposure to T. gondii (and other parasites!) and prevent contamination of the environment beyond your property if your cat becomes infected and is shedding oocysts (even though this usually only occurs once in the cat’s life, for a short period after the cat is infected for the first time).
• Cleaning litter trays – Remove faeces from litter trays twice daily and, when you clean the tray, disinfect it with boiling water. Even if a cat is shedding oocysts, this will prevent the oocysts from becoming infectious (sporulating). Wash your hands thoroughly after cleaning a litter tray (you may also want to wear gloves, particularly if you are at risk – see below). Dispose of cat waste and litter safely in a way that does not contaminate the environment (including waterways). There are a variety of ways to do this depending on the litter you use, where you live, the services available, and your situation etc. These include options such as bagging the cat waste and putting it into the bin to go to landfill (but this carries other environmental concerns) or composting. Note that for home composting, precautions must be taken to make this option feasible and safe, and compost that includes pet waste should not be used on edible plants. Commercial composting is another option, but you must make sure the service accepts cat waste and that the waste meets the required criteria for the commercial composting service (e.g., some litters may be acceptable but others not). It is important to research the options using reputable sources so you can choose the right option for your situation and undertake all the necessary actions. Do not flush cat waste/litter down the toilet or throw it out into the environment as this can contaminate the environment.
• Cover sandpits when not in use to stop cats toileting in the sand.
• If you are pregnant or have a compromised immune system – Consult your doctor and seek veterinary advice. Avoid changing cat litter if possible, or wear gloves and wash your hands afterwards.