The infection toxoplasmosis is caused by the Toxoplasma gondii parasite. Cats are the usual host for these parasites, but children, adults, and other animals can also be infected. Humans and animals can become infected if they swallow the microscopic eggs of the parasite or eat cysts in undercooked meats from cattle, sheep, pigs, or wild animals such as deer.
The T gondii parasite can only mature to an adult in the body of a cat. The adult parasite lives in the gut of cats, and the eggs enter the environment through the cat feces. The eggs must mature in the soil for 1 to 5 days before they become contagious for people or other animals. When a person or an animal other than a cat eats the mature egg, it hatches within the bowel and burrows through the bowel wall. When the parasite is in a human (the non-preferred host), it cannot mature to an adult, but instead becomes a cyst in a muscle or organ. These cysts can become reactivated later in life, especially if a person’s immune system is weakened by illness or medicines.
Humans can get the parasite by:
- Eating raw or undercooked meat that contains cysts
- Drinking untreated water contaminated with mature eggs
- Eating unwashed fruits and vegetables grown in contaminated soil
- Touching your mouth with your hand after handling soil or sand that contains mature eggs
If a pregnant woman becomes infected with T gondii, she can pass the infection to her unborn fetus.
Signs and Symptoms
When the parasite is passed from the pregnant mother to the unborn fetus, the infections are less frequent but more severe early in pregnancy, and more frequent but less severe in the later months. Most infants born with toxoplasmosis have no signs or symptoms at birth.
Some babies will have signs and symptoms that include:
- Swollen lymph glands
- Low number of blood platelets
- Enlargement of the liver and spleen
Although 70% to 90% of the infants born with toxoplasmosis do not have any signs or symptoms at birth, serious complications caused by inflammation of the eye and brain often appear in the ensuing months and years. These can include vision problems, varying levels of developmental delay, seizures, deafness, and blockage of cerebrospinal fluid pathways in the brain leading to hydrocephalus. Some infected fetuses may die in the uterus or within the first few days after birth.
When children or adults develop toxoplasmosis, illness is uncommon. When it does occur, it may look similar to infectious mononucleosis and include:
- Swollen lymph glands, particularly in the region of the neck
- Muscle aches and pains
- Sore throat
- Enlargement of the liver and spleen
- General feelings of being ill
A pregnant woman with toxoplasmosis may be symptom free, but she can still pass the infection to her unborn baby. This is most common when the infection occurs near the end of the pregnancy.
People with weakened immune systems can develop blindness because of cysts within the retina (the part of the eye involved in vision). Meningitis or encephalitis may be caused by cysts within the brain. Other complications include pneumonia or, less often, widespread infection involving many organs in the body.
How Is the Diagnosis Made?
The diagnosis of toxoplasmosis is made by blood tests that can detect antibodies to the parasite. These tests can be difficult to perform and interpret and should be done with the guidance of specialists in this field.
If you are pregnant and believe you may have become infected with T gondii, ask your doctor to test you for the presence of this parasite.
Older children and teenagers with a normal immune system do not require specific medical treatment for toxoplasmosis unless they are pregnant. All infected newborns should be treated to avoid eye problems and inflammation of the brain. Patients with a weakened immune system usually require treatment. Your pediatrician will often call in a specialist in infectious diseases to help decide on management.
The most common medicines used are a combination of pyrimethamine and sulfadiazine or clindamycin. Treatment continues for several months. Newborns may require treatment for a year. Pyrimethamine is always given with folinic acid (leucovorin) to prevent damage to the liver and bone marrow. In certain patients, corticosteroids may be prescribed for eye problems caused by the infection.
What Is the Prognosis?
Early treatment can be very successful for babies who are infected before birth, although many will develop eye or brain problems despite treatment.
Toxoplasmosis acquired after birth generally goes away on its own without any lasting complications. However, if your child has a weakened immune system because of, for example, a human immunodeficiency virus (HIV) infection or cancer chemotherapy, she is more likely to develop a severe form of the disease that can damage the brain, eyes, or other organs.
Pregnant women should not change cat litter boxes or do any gardening and landscaping to avoid being exposed to cat feces, which may contain these parasites. If these activities are unavoidable, wear gloves and wash your hands thoroughly afterward. If you do catch toxoplasmosis, early treatment can prevent many of the complications to the fetus.
To reduce the chances of ingesting foods with T gondii, cook all meat— beef, pork, lamb, and wild game—to an internal temperature of 150°F to 170°F until the meat is no longer pink.
Also, follow these recommendations:
- Wash or peel all fruits and vegetables.
- Take steps to prevent contaminating other foods with raw or undercooked meat.
- Wash your hands, cutting boards, other kitchen surfaces, and kitchen cutlery and utensils after handling and preparing raw meat, fruits, and vegetables.
- Wash your hands after gardening or having other contact with soil or sand in sandboxes.
To reduce the chances that your pet cats will become infected, feed them only commercially made cat food. Keep them from eating undercooked kitchen meat scraps or hunting wild rodents. Cats who go outdoors may be exposed to soil contaminated by eggs from infected cats’ feces.