Infectious DiseasesTier 2Disease (DEADMAN)

Emerging or less common infections - toxoplasmosis

Description

Toxoplasma gondii is a protozoan parasite causing mild/asymptomatic infection in immunocompetent hosts but significant disease in two vulnerable groups - primary infection during pregnancy (congenital toxoplasmosis risk) and reactivation in advanced immunosuppression (particularly cerebral toxoplasmosis in advanced HIV)

Common worldwide - seroprevalence varies with geography and diet (undercooked meat, oocysts from cat faeces)
Because past infection is common, the clinical concern is not the infection itself but who gets it and when:
- Reactivation of latent infection in the immunocompromised
- Primary infection in pregnancy (congenital transmission)

Transmission via undercooked meat (tissue cysts) or ingestion of oocysts from cat faeces (definitive host); the parasite establishes latent tissue cysts (particularly in brain and muscle) after primary infection, with reactivation occurring under significant T-cell immunosuppression

Serology (IgG/IgM) establishes exposure timing (relevant to assessing congenital transmission risk if infection occurs during pregnancy); cerebral imaging (MRI/CT) plus response to empirical treatment supports a diagnosis of cerebral toxoplasmosis in the appropriate advanced-HIV clinical context, given the difficulty of tissue biopsy confirmation
Primary maternal infection timing during pregnancy determines both transmission risk (increases with gestational age) and severity of fetal disease (more severe with earlier gestational infection despite lower transmission risk)

Cerebral toxoplasmosis (advanced HIV, typically CD4 <100): pyrimethamine-sulfadiazine (or alternative regimen) with folinic acid, alongside antiretroviral therapy initiation
Congenital toxoplasmosis prevention: dietary counselling (avoid undercooked meat, cat litter exposure) for seronegative pregnant women; confirmed maternal primary infection prompts treatment aimed at reducing vertical transmission and fetal disease severity

Cerebral toxoplasmosis (advanced HIV, a key opportunistic infection), congenital toxoplasmosis (chorioretinitis, intracranial calcification, hydrocephalus), space-occupying brain lesion differential in HIV (toxoplasmosis vs primary CNS lymphoma)

In advanced HIV with a new space-occupying brain lesion, cerebral toxoplasmosis and primary CNS lymphoma are the key differentials - empirical anti-toxoplasma treatment with clinical/radiological response at 1-2 weeks is a standard diagnostic approach, with biopsy reserved for cases not responding as expected

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