Toxoplasmosis - Causes of toxoplasmosis

The toxoplasmosis infection is caused by the Toxoplasma gondii (T. gondii) parasite.

The T. gondii parasite can be found in the faeces of infected cats and the meat of infected animals.

T. gondii can reproduce inside a cat's bowel. An infected cat can pass the parasite in its faeces for the following few weeks. The cat won't usually have any symptoms, so you may not know it's infected.

Infection via the food chain and environment

There are four ways the T. gondii parasite can enter the food chain and cause a toxoplasmosis infection. You can become infected by: 

• ingesting food, such as fruit and vegetables, water or soil contaminated with infected cat's faeces
• eating or handling raw or undercooked infected meat, usually pork, lamb or venison (grazing animals can become infected after eating contaminated grass or animal feed)
• using knives, cutting boards and other utensils that have been in contact with contaminated, undercooked or raw meat
• eating or drinking infected unpasteurised goats' milk or products made from it, such as cheese

There's also a small risk of the toxoplasmosis 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.

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 if you have previously had the infection
• 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.

Congenital toxoplasmosis

Congenital toxoplasmosis is where a baby is born with toxoplasmosis. The mother passes the infection to her baby through the placenta (the organ that links the mother's blood supply to her unborn baby's).

However, congenital toxoplasmosis can only occur if the mother becomes infected for the first time, either while she's pregnant or shortly before conceiving.

Congenital toxoplasmosis is more likely to occur if a woman becomes infected later in her pregnancy. For example, if you become infected around the time of conception, there's a less than 5% chance that your baby will also develop the infection.

However, if you become infected during the third trimester of your pregnancy (from week 27 until the birth), there's about a 65% chance your baby will also be infected.

One study calculated that for every week further along the pregnancy that the mother was infected, the likelihood of the toxoplasmosis infection being passed on to her baby increased by 12%.