Causes of toxoplasmosis 

Toxoplasmosis is caused by the Toxoplasma gondii (T. gondii) parasite. This is found in the poo (faeces) of infected cats and the meat of infected animals.

T. gondii can reproduce inside a cat's bowel and is passed out in its poo for a few weeks after it became infected. The cat won't usually have any symptoms, so you may not know it's infected. The parasites can survive outside in soil or water for many months.

The parasites can get into animal meat if an animal eats soil, grass, animal feed or another animal that has been contaminated by an infected cat's poo.

How you can get toxoplasmosis

You can get toxoplasmosis if the T. gondii parasites get into your mouth.

This can happen by: 

  • eating food (such as unwashed fruit and vegetables) or drinking water that's contaminated with infected cat's poo
  • getting your hands contaminated by touching soil or cat litter, and then putting them in or near your mouth
  • eating raw, cured or undercooked infected meat – particularly lamb and pork
  • accidentally getting the parasite in your mouth after handling contaminated meat, or handling knives, cutting boards and other utensils that have been in contact with contaminated meat
  • eating or drinking infected unpasteurised goats' milk or products made from it, such as cheese

There's also a small risk of the infection being passed from sheep during the lambing season. This is because the T. gondii parasite is sometimes found in the afterbirth and on newborn lambs after an infected sheep has given birth.

Can toxoplasmosis spread between people?

Toxoplasmosis can't be passed on through person-to-person contact. This means that:

  • you can't catch toxoplasmosis from coming into contact with an infected person
  • you can't pass toxoplasmosis on to your children 
  • it's not possible to pass the infection on through breastfeeding

However, in rare cases people have developed toxoplasmosis from an infected organ transplant or blood transfusion.

There's also a chance the infection could be passed to an unborn baby if the mother becomes infected while pregnant.

Can I be infected more than once?

After being infected, most people are immune to toxoplasmosis for the rest of their life. However, the parasites that cause the infection can remain inactive in the body for many years, and potentially for life.

These inactive parasites won't usually cause any problems, including for pregnant women who were infected before becoming pregnant, although there's a chance they could become active again if your immune system weakens. For example, the infection may start to cause problems if you get HIV or have chemotherapy.

Toxoplasmosis in pregnancy

If a pregnant woman becomes infected with toxoplasmosis, there's a risk the infection could spread to her baby through the placenta (the organ that links the mother's blood supply to her unborn baby's).

However, this can only occur if the mother becomes infected for the first time while she's pregnant or shortly before conceiving. This is thought to happen very rarely in the UK.

Even if you do become infected while pregnant, it doesn't necessarily mean the infection will spread to your baby. The chances of your child becoming infected are higher the later you become infected.

For example, the risk of passing the infection on is only around 10-15% if you become infected in the first 12-13 weeks of pregnancy, but can be as high as 70% if you become infected from weeks 26-28 onwards.

If your baby does become infected, it can cause a serious condition known as congenital toxoplasmosis. Read about the complications of toxoplasmosis for more information about this.

Page last reviewed: 24/06/2015

Next review due: 24/06/2017