In toxoplasmosis serology, low avidity IgG indicates a more recent infection. Which option reflects this concept?

In toxoplasmosis serology, low avidity IgG indicates a more recent infection. Which option reflects this concept?

• A. High Avidity IgG Indicates Recent Infection
• B. Low Avidity IgG Indicates A More Recent Infection
• C. IgM Is Never Present In Toxoplasmosis
• D. IgA Is The Primary Marker

Answer: (B)

The main idea is that antibody binding strength (avidity) matures over time after infection. Early after infection, toxoplasma-specific IgG bind more weakly (low avidity). As the immune response matures over weeks to months, these IgG antibodies gain stronger binding (high avidity). So finding low-avidity IgG points to a recent infection, while high-avidity IgG points to an older infection. This is exactly what the statement expresses, making it the best choice. In practice, avidity testing helps distinguish recent maternal infection from past infection, especially since IgM can be present for a long time or yield false positives. IgA isn’t used as the primary marker for dating toxoplasmosis.

The main idea is that antibody binding strength (avidity) matures over time after infection. Early after infection, toxoplasma-specific IgG bind more weakly (low avidity). As the immune response matures over weeks to months, these IgG antibodies gain stronger binding (high avidity). So finding low-avidity IgG points to a recent infection, while high-avidity IgG points to an older infection. This is exactly what the statement expresses, making it the best choice. In practice, avidity testing helps distinguish recent maternal infection from past infection, especially since IgM can be present for a long time or yield false positives. IgA isn’t used as the primary marker for dating toxoplasmosis.