Dangers of Toxoplasmosis and Pregnancy

Dr. Greene's Answer

Congratulations, Stephanie! Only 31 weeks to go! What a miracle — a new life is forming inside you! Once a baby arrives, changing diapers is a practical way to express love. In the meantime, NOT changing the kitty litter is another way you can express love to your baby.

Toxoplasma is a one-celled parasite whose primary host is the cat family. Infected cats usually have no symptoms, but may shed as many as 10 million egg-cysts in their feces each day for the three weeks that their acute infection lasts. After excretion, it can take from 1 to 21 days for the egg-cysts to ripen and become infectious (usually 2-8 days). The egg-cysts can survive for more than a year in moist soil. They are 0.0005 inches long, invisible to the naked eye.

If you get the microscopic egg-cysts on your hands, you can become infected by eating food you have handled. Inhalation of the cysts can also cause infection. Flies have been shown to aid the transmission of toxoplasmosis. Egg-cysts get on their feet and are deposited when they land on food. Directly changing the kitty litter accounts for many cases of human toxoplasmosis. There is a tiny risk from petting cats.

Other animals also get toxoplasmosis, including cows, pigs, chickens, and goats. Although they appear well, infectious tissue-cysts get in their muscles and milk. Outbreaks have been linked to consuming raw goat’s milk or undercooked meat. One study in Palo Alto, California showed cysts present in up to one third of pork chops. The cysts can survive for months at refrigeration temperatures. They are destroyed by cooking to 150 degrees.

The danger to your baby comes if you are infected for the first time after your baby was conceived, particularly in the first or second trimesters. Only about 15% of pregnant women already have antibodies to toxoplasma (sorry, Stephanie). The other 85% are susceptible to a first infection. As it turns out, about 0.4% of pregnant women acquire toxoplasmosis. Even if untreated, only a percentage of mothers will pass the infection on to their babies. The earlier the infection is acquired, the less likely that transmission will occur. However, the earlier the infection, the more likely severe disease will develop. Prompt treatment during pregnancy can help reduce the risk of severe disease in infected babies.

Congenital toxoplasmosis is estimated to occur in about 3000 babies in the United States each year. There is a wide spectrum of severity in these babies. Thankfully, over half of them are completely asymptomatic. Another third have only a mild form of the disease. About 10% have the severe form of congenital toxoplasmosis which can include blindness, mental retardation, or even death.

It is difficult for a pregnant woman to know if she has become infected. Only 10% ever have any symptoms, and these are mild (flu-like symptoms, muscle aches, generalized swollen lymph nodes). There are blood tests, however, that can clarify the situation. Two types of antibodies to toxoplasma are measured — IgG and IgM. If the IgG is negative, you do not now (and never have had) toxoplasmosis. If the IgG is positive, you have had the infection at some time. If the IgM is negative, it is almost certain that the infection was prior to conception. If the levels are high or there is any question, repeat or more advanced testing can further pinpoint the time of infection. Sometimes tests on the unborn baby’s blood or amniotic fluid may be obtained to look for infection in the baby.

It is wise for women to avoid kitty litter boxes when pregnant, and to wear gloves if they garden. Perhaps someone else could disinfect the litter box with boiling water every week during the first two trimesters. Having another person change the litter box daily can also help remove egg-cysts before they can mature and become infectious. Prevent your cat from eating undercooked meats and wild rodents to reduce your cat’s risk of becoming infected. Make sure meat is cooked to at least 150 degrees, and fruits and vegetables are well washed. Wash your hands and kitchen surfaces after handling uncooked meat or unwashed vegetables, and avoid touching your mouth in the meantime.

Above all, though, relax and enjoy the next 31 weeks as the miracle of new life is forming inside you. This complex and mysterious unfolding proceeds moment by moment, while you are awake and while you are asleep.