An infection caused by a single-celled parasite named Toxoplasma gondii that may invade tissues and damage the brain, especially of the fetus and newborn. The parasite Toxoplasma gondii is very common (more than 60 million people in the US carry it) but few are aware of it because the immune system often keeps the parasite from causing illness. The usual symptoms of toxo are similar to flu with fever, fatigue, headache, swollen lymph glands (lymphadenopathy), and muscle aches and pains (myalgia) that may last for a few days to several weeks.

Toxo can be contracted by touching the hands to the mouth after gardening, cleaning a cat's litter box, or anything that came into contact with cat feces. Toxo can also be contracted by eating raw or partly cooked meat, especially pork or lamb, or touching the hands to the mouth after contact with raw or undercooked meat. Persons with a weakened immune system are at risk for developing a severe case of toxo. At high risk therefore for severe toxo are:

* Children and adults with an inherited immune defect,
* Anyone with AIDS,
* Anyone receiving systemic (bodywide) chemotherapy,
* Anyone who has received a transplant and is on immunosuppressive therapy (to prevent rejection of their transplant), and
* The fetus and newborn.

Toxoplasma gondii is a well-known teratogen -- an agent that can cause birth defects. If a woman is pregnant when she is infected, the parasite can cross the placenta from her to the baby with sometimes catastrophic consequences. Children born with toxo (congenital toxoplasmosis) can have mental retardation, convulsions (epilepsy), spasticity, cerebral palsy, and partial or complete deafness and blindness.