Toxoplasmosis
Infection by *Toxoplasma gondii*; usually asymptomatic in immunocompetent hosts but causes retinochoroiditis, cerebral toxoplasmosis in advanced HIV, and congenital infection. Pyrimethamine-based regimens with folinic acid rescue are standard for cerebral disease; specialist care in pregnancy.
Key Facts
Key points
- Serology: IgG indicates past exposure; IgM patterns need expert interpretation in pregnancy.
- Cerebral toxoplasmosis (HIV): sulfadiazine 1–1.5 g QDS + pyrimethamine 200 mg loading then 50–75 mg OD + folinic acid 15–25 mg OD** (rescue) for ≥6 weeks induction — then maintenance until immune reconstitution.
- Alternative: co-trimoxazole 960 mg BD** can be used for treatment/prophylaxis per guideline.
- Pregnancy: spiramycin early infection (where available) vs pyrimethamine/sulfadiazine/folinic acid after 18 weeks — regional protocols — always specialist.
- Primary prophylaxis in HIV when CD4 <200: co-trimoxazole 960 mg OD** (or thrice weekly per local policy).
Overview
Transmission
Oocysts in cat faeces/contaminated soil; tissue cysts in undercooked meat; transplacental.
Immunopathogenesis
Reactivation of latent cysts when cell-mediated immunity fails.
Clinical Presentation
Immunocompetent
Often subclinical; lymphadenopathy; chorioretinitis.
Immunosuppressed
Ring-enhancing brain lesions (MRI), confusion, focal neurology.
Congenital
Chorioretinitis, hydrocephalus, intracranial calcification.
Differential Diagnosis
| Brain lesion HIV | Notes |
|---|---|
| Primary CNS lymphoma | Single lesion more typical; thallium PET |
| TB | Basal meningitis pattern |
| PML | White matter, JC virus |
Diagnosis / Investigation
Imaging
MRI brain with contrast.
HIV
CD4 count; if not known HIV, test.
Ophthalmology
Urgent review if ocular symptoms.
Management
Cerebral toxoplasmosis
- Start co-trimoxazole if pyrimethamine/sulfadiazine unavailable — per BASHH/HIV guidelines.
Steroids
Controversial around mass effect — specialist only.
ART
Start/restart when feasible; watch for IRIS.
Prognosis
Cerebral toxoplasmosis improves with therapy and immune recovery; congenital outcomes depend on gestational timing of acquisition.
Other Relevant Information
Pregnancy counselling
Avoid undercooked meat; hygiene around cats; serial ultrasound in seroconversion — specialist care.