Diagnosis of Toxoplasma infection can be established by the detection of IgM- and IgG-antibodies in the serum. Detection of IgA positivity in serum is common during acute infection. After primary infection the specific IgG response persists. This may sometimes make it difficult to diagnose toxoplasmosis only by serology. Polymerase chain reaction diagnostic methods in peripheral leukocytes has recently been developed (and described elsewhere in this book). The sensitivity is, though, sometimes lower than the serological

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diagnostic, and in several studies it has been reported to vary between 70 and 80%. Toxoplasma trophozoites can be found histologically by using antigen-specific staining methods. In CNS infection, computerized tomography scan with intravenous contrast is an important instrument for diagnosis. The typical picture includes multiple lesions surrounded by contrast enhancement. Pneumonia due to Toxoplasma in these patients is often atypical with bilateral infiltrates of the lungs. Most cases of pneumonia can be diagnosed by antigen detection in bronchoalveolar lavage (BAL), and myocarditis by specific antigen staining of histology sections. Toxoplasma gondii trophozoites, pseudocysts, and cysts can also be visualized in hematoxylin and eosin or Giemsa staining, both in BAL and in heart biopsies.

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