Toxoplasmosis (Toxoplasma gondii)

1. What is Toxoplasmosis and how it happens_?_

T. gondii, a microscopic parasite, remains unseen to the naked eye. In most healthy individuals, infection either goes unnoticed or results in a mild flu-like illness. However, when a pregnant woman contracts the parasite and transmits it to her unborn child or when an individual with a weakened immune system (immunocompromised) becomes infected, severe complications can ensue.

T. gondii has a global presence, with up to 60% of the population in some countries being affected. In the United States, the Centers for Disease Control and Prevention estimates that over 40 million people carry the infection, with approximately 11% of those aged 6 and older having had toxoplasmosis. Transmission can occur through various means, including:

1. Consuming contaminated food, particularly undercooked or raw meat like pork, lamb, and venison.
2. Ingesting unwashed fruits and vegetables grown in soil contaminated with the parasite.
3. Contact with soil that is contaminated.
4. Drinking contaminated water.
5. Consumption of unpasteurized milk.
6. Handling cat litter that may be contaminated.
7. Play in sandboxes that are contaminated.
8. Transmission from mother to child during pregnancy.
9. Rarely, transmission during organ transplantation or blood transfusion.

The primary hosts for T. gondii are domestic and wild cats. In cats, the parasite multiplies after they consume infected birds, rodents, or contaminated raw meat, leading to the formation of eggs encased in protective coverings (oocysts). During an active infection, millions of microscopic eggs can be released into the cat's stool for several weeks. These eggs become infective within days and can remain viable for several months. However, in all other hosts, including humans, T. gondii goes through a limited portion of its lifecycle, forming dormant cysts in muscles, the brain, and eyes. The host's immune system keeps these cysts in check, preventing further infection. The dormant stage can persist for the host's lifetime unless their immune system is compromised.

In individuals with weakened immune systems, such as those with HIV/AIDS, undergoing chemotherapy, recent organ transplant recipients, or on immunosuppressant medications, an initial or reactivated T. gondii infection can lead to significant symptoms and complications. It can affect the nervous system and eyes, resulting in headaches, seizures, confusion, fever, encephalitis, loss of coordination, and blurred vision.

Pregnant women who become infected face a 30-40% risk of passing the infection to their unborn child. If the congenital infection occurs early in the pregnancy, it can lead to miscarriages, stillbirths, or severe complications in the newborn, including mental retardation, seizures, blindness, and an enlarged liver or spleen. Many infected babies, especially those exposed later in pregnancy, may appear healthy at birth but may develop symptoms such as severe eye infections, hearing loss, and learning disabilities in the years that follow.

2. How is the test used?

A toxoplasmosis test serves to identify a current or past infection involving the microscopic parasite Toxoplasma gondii. It is commonly conducted for the following reasons:

1. To assess a woman's exposure to Toxoplasma gondii before or during pregnancy, and during pregnancy if exposure is suspected.
2. For individuals with compromised immune systems (immunocompromised) who exhibit flu-like symptoms.
3. To diagnose toxoplasmosis in someone presenting signs or symptoms.
4. In the case of an unborn baby, amniotic fluid may be tested.

Various testing methods are available for detecting T. gondii. The selection of tests and samples collected is contingent on the individual, their symptoms, and the clinical judgment of the healthcare provider.

3. How can the test be interpreted?

Caution is essential when interpreting the outcomes of toxoplasmosis testing. In cases of immunocompromised individuals, the antibody response to a T. gondii infection might be weak, resulting in lower-than-expected levels of IgM and IgG, even when they have an ongoing case of toxoplasmosis.

Also, False positives are a possibility. Typically, when IgM antibody tests yield positive results, it is advisable to confirm these findings through an alternative testing method, often by sending the sample to a specialized reference laboratory that focuses on toxoplasmosis testing.

In newborns, IgM antibodies are the sole class of antibodies produced. The presence of Toxoplasma IgM antibodies in a newborn signifies a congenital infection.

4. Can toxoplasmosis be transmitted to others?

T. gondii is not typically transmitted directly from one person to another, except in cases of mother-to-child transmission. Almost all instances of infection result from the consumption, ingestion, or handling of contaminated items.

5. Can toxoplasmosis be effectively treated?

Treatment is generally unnecessary for most healthy individuals, but options are available for those with weakened immune systems, pregnant women to reduce the risk of fetal transmission, and newborns with congenital toxoplasmosis. For further information on treatment, you can refer to the Mayo Clinic or CDC websites.

6. What should people do to prevent toxoplasmosis infection?

Here are the recommended actions to take:

1. Delegate cat litter box cleaning to someone else if possible. If not, wear gloves and change the litter daily to prevent the eggs from becoming infective.
2. Keep your cat indoors whenever feasible to deter hunting and potential ingestion of contaminated soil. Avoid feeding your cat raw meat.
3. Refrain from acquiring a new cat or handling stray cats during pregnancy.
4. Cover a child's sandbox when not in use to prevent it from being used as a litter box.
5. Wear gloves while gardening.
6. Avoid consuming raw or undercooked meat.
7. Thoroughly clean cutting boards, hands, and utensils used for raw meat preparation with hot, soapy water, and be diligent to prevent cross-contamination.
8. Do not consume unpasteurized milk.
9. Wash and/or peel fruits and vegetables before consumption.

7. Are there alternative methods for toxoplasmosis testing?

Additional tests, including the IgG avidity test, may be conducted by a reference laboratory to provide further confirmation of a T. gondii infection. In rare instances, a tissue sample from a suspected Toxoplasma parasite-infected area may be obtained through biopsy. This sample can undergo culturing and/or staining and examination under a microscope to detect the presence of the parasite. Typically, these procedures are reserved for challenging diagnostic cases.