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Toxoplasmosis Testing

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Also known as: Toxoplasma gondii, T. gondii
Formal name: Toxoplasma gondii Antibodies, IgG, IgM; Toxoplasma gondii Molecular Detection by PCR

The Test Sample

What is being tested?

Toxoplasmosis is an infection caused by the parasite Toxoplasma gondii. Testing detects antibodies in the blood that are produced in response to an infection or detects the genetic material (DNA) of the parasite in the blood. Testing is performed in order to detect and diagnose a current or past infection.

T. gondii is a parasite that cannot be seen with the naked eye (microscopic). In most healthy humans, the infection either causes no symptoms or results in a mild flu-like illness. When a pregnant woman becomes infected, however, and passes it to her unborn child, or a person with a weakened immune system (immunocompromised) becomes infected, the parasite can cause severe complications.

T. gondii is very common. It is found throughout the world and in some countries has infected up to 95% of the population. In the United States, the Centers for Disease Control and Prevention estimates that about 23% of those 12 years of age and older have had toxoplasmosis. The infection can be acquired by ingesting contaminated food or water, especially eating raw or undercooked meat, by handling contaminated cat litter or playing in contaminated sandboxes, by transmission from mother-to-child, and rarely may be transmitted during an organ transplantation or blood transfusion.

The definitive host for T. gondii is wild and domestic cats. When cats become infected by eating infected birds, rodents, or contaminated raw meat, T. gondii replicates and forms eggs encased in protective coverings (oocysts). During an active infection, millions of microscopic oocysts may be released for several weeks into the cat's stool. The oocysts become infective within a couple of days and can remain viable for several months. In all other hosts, including humans, T. gondii only goes through a limited portion of its lifecycle and then forms inactive cysts in the muscles, brain, and eyes. The host's immune system keeps these cysts dormant and protects the body against further infection. The dormant stage can persist throughout the host's life, unless the immune system becomes compromised.

An initial or re-activated Toxoplasma gondii infection can cause significant symptoms and complications in people with weakened immune systems, such as those who have HIV/AIDS, are undergoing chemotherapy, have had a recent organ transplant, or are on immunosuppressant medications. It can affect the nervous system and eyes, causing headaches, seizures, confusion, fever, encephalitis, loss of coordination, and blurred vision.

When a woman becomes infected during pregnancy, there is a 30-40% chance that the infection will be passed to her unborn child. If this congenital infection occurs early in the pregnancy, it can cause miscarriages or stillbirths or can lead to severe complications in the newborn, including mental retardation, seizures, blindness, and an enlarged liver or spleen. Many infected babies, especially those exposed later in the pregnancy, will appear normal at birth but may develop symptoms, such as severe eye infections, hearing loss, and learning disabilities, years later.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm. Rarely, a cerebrospinal fluid (CSF) sample is collected from the lower back using a procedure called a lumbar puncture or spinal tap, or a sample of amniotic fluid is collected from a pregnant woman using amniocentesis.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.