A New Test For Toxoplasmosis

active infection. Unfortunately, IgM antibodies to Toxoplasma gondii can last for a year or more making it impossible to tell if a pregnant woman has had a recent infection which could endanger the life of the baby or one a long time ago with no threat of infecting the child.

Fortunately, studies conducted many years ago demonstrated that antibodies of the IgG type are produced that will bind more strongly to the infecting microorganism's proteins as the infection is eliminated and the person recovers from the infection. These antibodies are called high-avidity antibodies. If a person has greater than 30 percent high-avidity antibodies to a particular microorganism they have been infected some time in the past. These high-avidity antibodies are tightly bound to Toxoplasma gondii's proteins and even urea won't release the antibodies from their protein. Low-avidity antibodies that form early in an infection are easily removed from their Toxoplasma gondii's proteins by urea.

Researchers have used this knowledge to make a better test for Toxoplasma gondii infections. By adding urea to a mixture of patient serum containing antibodies to Toxoplasma gondii and Toxoplasma gondii proteins they are able to determine how much high-avidity antibodies the pregnant woman is producing. If the woman is making more than 30 percent high-avidity antibodies she was infected some time in the past and would not need to be treated to prevent infection of her baby (fetus). However, if the pregnant woman is producing less than 30 percent high-avidity antibodies to Toxoplasma gondii she has just recently been infected by Toxoplasma gondii and would need to be treated (spiramycin) to prevent the parasite from infecting her baby (fetus).

This particular means of testing for recent and past infections is not limited to just Toxoplasma gondii infections. Many other infections are difficult to diagnose because of these long lasting IgM antibody responses. This method of testing could be used in many other more common infections. This testing method is not currently approved for use in the United States however, with further studies it could be a common means of testing for infections.

For more information on Toxoplasma gondii infections go to the following websites.
Toxoplasmosis- CDC
Toxoplasmosis- AVMA

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