Toxoplasmosis

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Also known as: Toxoplasmosis gondii
Formal name: Toxoplasmosis gondii Antibodies, IgG, IgM; Toxoplasmosis gondii Molecular Detection by PCR
Related tests: TORCH; CSF Analysis; Aminiotic Fluid Analysis

At a Glance

Why Get Tested?

  • To detect a Toxoplasma gondii infection in an immunocompromised patient, particularly patients with Human Immunodeficiency Virus (HIV) or patients that are to undergo heart, lung, kidney or lung tranplantation
  • To determine the cause of a glandular fever like illness associated with swollen lymph glands, fever, lethargy and an enlarged spleen and/or liver
  • To determine the cause of unexplained chorioretinitis
  • To detect the acquisition of infection in a pregnant woman for the purpose of initiating treatment to preventing infection in the unborn child

When to Get Tested?

  • Patients with advanced HIV infection should be tested
  • Patients who are undergoing solid organ transplantation
  • Patients with unexplained chorioretinitis (inflammation of the back of eye)
  • Routine testing of pregnant women is not recommended for complex reasons outlined below

Sample Required?

A blood sample drawn from a vein in your arm; sometimes cerebrospinal fluid (CSF), amniotic fluid, or vitreal aspirate if infection of the brain, unborn child or eye respectively are suspected

Test Preparation Needed?

None

The Test Sample

What is being tested?

Toxoplasmosis testing is performed in order to detect and diagnose a current or past Toxoplasma gondii infection. T. gondii is a microscopic parasite that infects cats and can be found in the soil. 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 becomes infected, the microorganism can cause severe complications.

T. gondii infection is relatively common and the vast majority of people do not have symptoms when they acquire it. In Australia, 20-40% of women of child bearing age have evidence of previous infection. The infection can be acquired by ingesting contaminated food or water, especially eating raw or undercooked meat, by handling contaminated cat litter, by transmission from mother-to-child, and rarely may be transmitted during an organ transplantation or blood transfusion.

A definitive host is an animal in which all stages of a parasites lifecycle occur. 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 those 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 the 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 learning difficulties, 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. In Australia, however, the risk of acquiring toxoplasmosis whilst pregnant is extremely low.

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 by a doctor from the lower back using a procedure called a lumbar puncture or a sample is taken from the eye in a procedure called a vitreal aspirate. To diagnose infection in an unborn baby, a sample of amniotic fluid is collected via  amniocentesis.

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

No test preparation is needed.

The Test

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

NEW REFERENCE

Seroprevalence of varicella zoster virus, parvovirus B19 and Toxoplasma gondii in a Melbourne obstetric population: implications for management.  Harin Karundeewa, David Siebert, Rachel Hammond, Suzanne Garland and Heath Kelly. Aust NZ J Obstet Gynaecol  2001; 41: 1: 23-28