Toxoplasmosis and cats

Toxoplasmosis is a fairly well known but very misunderstood parasitic infection. Discover the truth behind the myths and how to protect yourself.

Toxoplasmosis toxoplasma gondii image

Of all of the conditions that can affect cats and humans, toxoplasmosis is probably the most widely known. Whilst knowledge of toxoplasmosis is quite wide spread, it is not always very well understood. The good news is that the risk of infection from a cat is very small, and humans are far more likely to become infected from other sources, including eating raw or undercooked meat, or gardening.

What is toxoplasmosis?

Toxoplasmosis is a zoonotic disease, which means it can pass between different species of animal. In this case it is the transmission from cats to humans that we are considering.

Toxoplasmosis comes from a single celled microscopic parasitic organism called toxoplasma gondii. Toxoplasma gondii is a wide spread parasite that exists in most parts of the world and is not especially uncommon.

Since parasites live off their host organisms, it is not in a parasite’s best interests to cause significant harm to its host. Toxoplasma gondii is a relatively well adapted and effective parasitic organism and it manages to live in reasonable harmony with its host, most of the time.

Toxoplasma gondii is quite an unusual parasite because it can live in virtually any animal. Most parasites are species specific, and are only able to survive in the one species they have evolved to live off.  Nevertheless, whilst it can infect any animal, toxoplasma gondii must enter a cat in order to complete its life cycle as the parasite is only able to reproduce in the body of a cat. This is presumably why most people incorrectly consider toxoplasmosis as something that only comes from cats.

How do cats get infected with Toxoplasmosis gondii?

Cats are usually infected by eating meat that has toxoplasmosis in it. Toxoplasmosis is very common in mice, voles and other small prey. It is also very common in sheep, pigs and domestic farm animals. Outdoor cats and cats that are fed raw or undercooked meat are at risk of toxoplasmosis infection. Once inside the cat, the toxoplasma gondii can reproduce, and the additional eggs produced are shed in the cat’s feces. Therefore any cats sharing litter trays are likely to pick up the infection from each other (this is another example of why our cats never share litter trays).

Once infected there are rarely ever any symptoms of the infection and most cats will fight off the parasite in their own time and without treatment, provided they are not being reinfected with more parasites from their food or litter tray habits.

Toxoplasmosis diagram 1
Toxoplasmosis cycle
Toxoplasmosis diagram 2
Toxoplasmosis cycle
Toxoplasmosis in mice
Toxoplasmosis in mice 

The above images are courtesy of icatcare international, an excellent source of information on all things feline.

Toxoplasmosis in humans

It is possible for humans to become infected with toxoplasma gondii. Fortunately, the parasite is not capable of reproducing within humans, so its life cycle will be limited. As long as the human is not constantly exposed to sources of new toxoplasmosis infection, the life cycle should be relatively short. Most cases of toxoplasmosis in humans are actually not caused by contact with cats. Most cases are from consuming undercooked meat or from soil on fruit and vegetables, or direct contact with soil. Sources of infection in humans include:

  • Meat

  • Soil on fruit and vegetables

  • Contact with soil (gardening)

  • Infected water

  • Unpasteurised milk


Is toxoplasmosis in humans harmful?

Fortunately, in the vast majority of cases, an infection of toxoplasmosis causes no symptoms at all and is naturally dealt with by the body’s own immune system, and the infected human never knows anything about it! However, there are some cases where toxoplasmosis can cause problems. These include humans with suppressed or ineffective immune systems, and the unborn babies of pregnant women.

Toxoplasmosis in human pregnancy

If a pregnant woman is infected with toxoplasmosis for the first time whilst she is already pregnant, the infection can pass to the foetus and this happens in about 20-50% of cases. Fortunately there is usually no effect on the foetus, but in a minority of cases it can result in abortion, birth defects, ocular problems, or neurological issues. We always advise on wearing gloves to change litter trays, keeping litter tray hygiene excellent by changing litter daily and disinfecting regularly and if at all possible, pregnant women should avoid changing litter trays as a precaution.


Does contact with cats increase the risk of toxoplasmosis infection?

Recent research has shown that contact with cats, or owning a cat, does not increase the risk of toxoplasmosis gondii infection in humans. Studies have show that:

  • It is very rare for cats to shed toxoplasmosa gondii oocysts (eggs) in their feces. In a study of 206 cats, where nearly 25% had been infected with toxoplasma gondii, none were found to be shedding eggs in their feces.

  • Vets working with cats are no more likely to be infected with toxoplasmosis than those not working with cats

  • Even where a cat is infected, stroking the cat did not spread the infection from cat to human - even when the cat was found to be shedding eggs in their feces, there were none found on the coat/fur

  • It is much more common for humans to become infected from eating raw or undercooked meat.

How to reduce your risk of Toxoplasmosis infection

  • Do not eat raw or undercooked meat

  • Wash fruit and vegetables thoroughly to ensure all soil is removed before cooking or eating

  • Wash your hands thoroughly after handling meat

  • Do not drink dirty water

  • Wear gloves when gardening and wash hands thoroughly afterwards

  • Change litter trays daily, and disinfect thoroughly on a regular basis

  • Always wear gloves to change litter trays

  • Do not feed your cat raw or undercooked meat


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