Toxoplasmosis

September 2005     View PDF     En español
Reprinted from www.aidsmeds.com, US

How is toxoplasmosis diagnosed?

A blood test can be ordered to check for the presence of antibodies to Toxoplasma gondii (including on cats & birds). However, just because someone has antibodies to this organism does not mean that they will experience disease. Approximately 40% of all people living in the United States have been exposed to toxoplasma gondii at some point in their lives. Only people with compromised immune systems, particularly HIV+ patients with T-cell counts below 50, are at risk for developing toxoplasmosis, the active form of disease caused by this organism. In some cases, active disease can be caused by a recent exposure, perhaps from eating undercooked meat. It’s also possible that harmless amounts of toxoplasma gondii in the body can take advantage of the immune system being suppressed, begin reproducing, and cause active disease.

To diagnose toxoplasma encephalitis, a CT or MRI scan is usually performed. Toxoplasma gondii can cause multiple lesions on the brain. However, it can be difficult to tell the difference between toxoplasmosis of the brain and other central nervous system disease, such as lymphoma. Newer imaging devices, such as PET or SPECT scans, can help distinguish between toxoplasma encephalitis and other central nervous system disease.

If toxoplasmosis of the brain is suspected, based on a patient’s symptoms at scan results, treatment will likely be started immediately, even if doctors can’t confirm the diagnosis. A brain biopsy is only necessary to establish the diagnosis if the patient does not respond to treatment. A biopsy may be required to diagnose toxoplasmosis of other tissues in the body, such as the lungs.