Do these EBV and Toxoplasma serologies prove active tissue infection?

Serologic results for EBV and Toxoplasma gondii primarily describe immune exposure; they require clinical context before being used to infer current disease, particularly in an older adult in whom alternative causes of symptoms may be common.

Clinical interpretation

• EBV early-antigen (EA) IgG: Elevated or detectable EA IgG is compatible with EBV reactivation or another active EBV state, but is not specific for either. EA IgG commonly declines within 3–6 months after acute infection, yet remains detectable for years in about 20–30% of otherwise healthy previously infected people. Antibody levels may also fluctuate and do not consistently track with EBV DNA.
• Toxoplasma serology: IgG-positive/IgM-negative results usually favor prior, rather than acute primary, infection. IgG may persist long term or lifelong, whereas absent IgM reduces the likelihood of recent acquisition. This pattern does not date the infection precisely. IgM performance is assay-dependent; reported point-of-care IgM sensitivity in an acute-infection cohort ranged from 28% to 100%.

Mechanistic and diagnostic implications

• EBV serology cannot localize virus to a diseased organ. In suspected EBV-associated tissue disease, lesion morphology and immunophenotyping with EBER in-situ hybridization are central because they identify EBV-infected cells within the affected tissue. Blood EBV DNA can be supportive but is not tissue proof.
• For suspected toxoplasmosis, confirmation should match the syndrome and sampled compartment. A positive PCR supports infection in that specimen; a negative test does not reliably exclude disease. For CNS disease, reported CSF PCR sensitivity is about 50%, despite high specificity.

Bottom line

• EBV EA IgG elevation and Toxoplasma IgG positivity with negative IgM are contextual clues, not standalone evidence of active tissue infection. Compatible symptoms, timing, immune status, imaging, and targeted molecular or tissue testing should determine whether further investigation is warranted.