Toxoplasmosis, caused by the protozoan parasite Toxoplasma gondii, can affect many bird and animal species, including humans. There are two main periods of the parasite lifecycle. The first is the oocyst: you may think of this as a sort of egg. The second period is the tissue stage of the parasite: this occurs within body tissues of infected animals. Cats become infected usually by eating meat containing the tissue stages of the parasite, either through hunting activity or by being fed raw meat. Infection usually occurs in young cats and they often do not show signs of illness. Once the parasite matures, oocysts are shed in cat faeces for 1 to 2 weeks. This shedding is generally limited to the first time cats are infected; if they continue to eat contaminated meat, shedding does not occur again.
However cats that have a suppressed immune system (e.g. severe illness, FeLV or FIV infection, steroid/prednisolone treatment) may be able to repeatedly shed oocysts. Oocysts in cat faeces take 1 to 5 days to become infective, and can remain infective in the environment for over a year. The oocysts are then picked up by other animals from the environment, for example by grazing animals, rodents running through contaminated soil or dogs eating cat poop. Tissue stages develop in the muscle, rodent gets eaten by cat, cycle starts over again. Once infective, occysts can become a danger to humans, particularly pregnant women.
What Are the Symptoms of Toxoplasmosis? What Are the Dangers During Pregnancy?
Like healthy cats, most healthy humans infected with Toxoplasma don’t show symptoms of disease. The parasite goes into tissues and remains dormant there without causing any problems. Some people do get a mild disease, which can include a fever, swollen glands (lymph nodes), muscle and/or joint pain and tummy pain due to temporary enlargement of the liver or spleen.
In immunosuppressed individuals (e.g. people with AIDS, transplant recipients or people undergoing chemotherapy) or when infected during pregnancy, the consequences of toxoplasmosis can be much more severe.
Infection for the first time during pregnancy can lead to abortion, stillbirth, brain damage, blindness or developmental disorders that only become apparent later in life. This is due to the parasite crossing the placenta and infecting the developing baby. This is extremely unlikely to occur in mothers that have been infected with Toxoplasma before falling pregnant, since the immune system can take care of a repeated infection.
Although not performed routinely in Australia, doctors can test expectant mothers for evidence of past Toxoplasma infections and if positive, the risk to the baby is minimal (because you need to be infected for the first time during pregnancy).
How is Toxoplasmosis Transmitted to Humans?
Humans can be infected from old cat faeces, after the oocysts have had time to mature. However multiple studies have shown that the most common route of infection in people is from eating meat, especially lamb and pork, infected with the dormant tissue stages of the parasite. In fact, most of these studies also showed that living in a household with a cat, particularly an indoor cat (with no access to hunting), was not a significant risk factor for infection.
Infections can also occur by eating unwashed fruit and vegetables in contact with soil contaminated with oocysts, drinking contaminated water or by drinking unpasteurized milk, especially goat’s milk. Rarely, toxoplasmosis has occurred through organ transplantation or blood transfusion.
How to Minimise Your Risk of Toxoplasmosis During Pregnancy:
- Cook all meat thoroughly
- Don’t mix kitchen surfaces and utensils used for preparing raw meat with those used for cooked meat (use a new knife and chopping board)
- Wash all fruit and vegetables thoroughly before eating
- Wear gloves when gardening (stray or roaming cats are more likely to be hunters and may use your garden beds as a litter box, thereby contaminating the soil for up to a year or more)
- Similarly avoid sandpits and keep sandpits covered (giant litter trays for outdoor cats)
- Only drink pasteurized milk (especially goat’s milk)
- Keep your cat indoors to reduce hunting (one of the many benefits of having an indoor cat!)
- Only feed your cat a commercial diet or cooked meat, no raw meat
- Clean the litter tray daily or twice daily (because it takes 1 to 5 days for oocysts to mature) and wear gloves. Or better yet, get someone else to change it!
- Wash your hands after cuddling your cat. However because cats are naturally so clean, it is unlikely for them to have faecal matter on their coats.
- If you are still worried, talk to your vet about testing your cat to see if it has been infected in the past. Remember, a healthy cat will only shed oocysts for 1 to 2 weeks after being infected for the first time.
So now you know the facts about toxoplasmosis and pregnancy. Although your cat can harbour this parasite, raw meat poses more of a threat. Practice good hygiene, particularly when preparing meat and gardening, and you will minimise the risk of this disease to yourself and your developing child. But it is also wise to get somebody else to change the litter tray – just to be safe. What a great excuse!