Paper II
Question
Lab diagnosis of toxoplasmosis
Answer
Laboratory diagnosis of toxoplasmosis (Toxoplasma gondii):
- Serology — IgM ELISA indicates recent infection; IgG indicates past infection; IgG avidity testing helps date the timing of infection (low avidity suggests recent infection within the past few months), particularly important in pregnancy for assessing fetal risk.
- PCR — on amniotic fluid for suspected congenital infection, or on CSF/blood/tissue in immunocompromised patients with suspected reactivation disease.
- Imaging — CT/MRI showing characteristic ring-enhancing lesions in toxoplasma encephalitis (AIDS patients), combined with response to empirical treatment as a pragmatic diagnostic approach.
- Histopathology — tissue biopsy demonstrating tachyzoites/bradyzoite cysts in selected cases.
- Sabin-Feldman dye test — a historical reference serological test (rarely used now, largely superseded by ELISA).