Toxoplasmosis
Toxoplasmosis is infection with the protozoan Toxoplasma gondii, acquired from undercooked meat or cat feces, causing a mononucleosis-like illness in immunocompetent hosts, reactivation encephalitis with ring-enhancing brain lesions in advanced HIV, and a severe congenital syndrome after maternal primary infection in pregnancy. Diagnosis in CNS disease is largely presumptive on serology, imaging, and empiric treatment response, and management is pyrimethamine-sulfadiazine-leucovorin, with prevention centered on CD4-based prophylaxis and food/cat-litter precautions in pregnancy.
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What this article covers
- Overview
A protozoan with three distinct clinical faces: Toxoplasma gondii causes a self-limited mononucleosis-like illness in immunocompetent hosts, reactivation encephalitis with multiple ring-enhancing…
- Epidemiology
Reactivation CNS disease occurs in advanced HIV: median CD4 count at diagnosis of toxoplasmic encephalitis is approximately 50 cells/mcL, occurring almost exclusively in patients already Toxoplasma IgG seropositive.
- Risk factors
Advanced immunosuppression with CD4 count <100/mcL: the dominant risk factor for reactivation toxoplasmic encephalitis, particularly when combined with positive baseline Toxoplasma IgG serology.
- Pathophysiology
Ingested tissue cysts release organisms in the gut: Toxoplasma gondii disseminates from the intestine, converts to the rapidly dividing tachyzoite form during acute infection, then encysts as latent…
- Clinical features
Immunocompetent primary infection: most cases are asymptomatic; when symptomatic, a heterophile-negative mononucleosis-like syndrome with fever, malaise, and lymphadenopathy predominates.
- Differential diagnosis
Primary CNS lymphoma: the most important mimic of toxoplasmic encephalitis in AIDS; typically a single lesion rather than multiple, and PET/thallium uptake is positive in lymphoma but negative in…
- Diagnosis
CNS/reactivation disease is a presumptive clinical diagnosis established by the combination of positive Toxoplasma IgG serology, compatible multiple ring-enhancing lesions on MRI, and…
- Management
First, start induction therapy for confirmed or empirically treated CNS disease with a three-drug regimen for at least 6 weeks (longer if disease is extensive or the 6-week response is incomplete)…
- Complications
Mass effect and herniation from expanding CNS lesions: untreated or advanced encephalitis can raise intracranial pressure and cause herniation.
- Prognosis
CNS disease responds predictably to therapy: effective anti-toxoplasma treatment produces clinical and radiographic improvement within 10 to 14 days; failure to respond in this window should prompt reconsideration of the diagnosis.
- Prevention
Primary prophylaxis in HIV: start trimethoprim-sulfamethoxazole double-strength tablet PO once daily in any HIV-infected adult with CD4 count under 100/mcL and positive Toxoplasma IgG serology…
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