Infectious Disease

Toxoplasmosis

Toxoplasma gondii infection is usually asymptomatic or mild in immunocompetent people, but needs specialist management when it affects the eye, brain, pregnancy or fetus; keep these pathways separate.

In a nutshell

Toxoplasmosis is usually asymptomatic or mild in immunocompetent people. It becomes high risk in advanced immunosuppression, pregnancy, congenital infection and ocular disease. Use reference-laboratory confirmation for difficult serology, MRI and specialist presumptive treatment for cerebral disease, urgent ophthalmology for visual symptoms, and separate fetal-medicine pathways for pregnancy; routine antenatal screening is not recommended in the UK.

Classic presentation

A person with advanced HIV and a low CD4 count develops headache, seizure and hemiparesis; MRI shows multiple enhancing lesions and Toxoplasma IgG is positive. Alternatively, a pregnant person has discordant IgM/IgG after a flu-like illness and needs urgent reference-laboratory and fetal-medicine assessment.

Key points

Acquire infection from cat-faeces-contaminated soil or produce and undercooked meat; casual contact with cats or infected people does not transmit it.
IgG indicates exposure and IgM can persist; do not diagnose recent primary infection or make pregnancy decisions from a single IgM result.
Advanced HIV can cause cerebral toxoplasmosis with multiple enhancing lesions; primary CNS lymphoma is the key competing diagnosis.
Cerebral disease needs specialist pyrimethamine plus sulfadiazine and folinic acid, usually for at least 6 weeks, or a specialist alternative; folinic acid is mandatory.
UK antenatal toxoplasmosis screening is not routine. Suspected pregnancy infection needs specialist reference-laboratory and fetal-medicine assessment.
Active ocular disease is urgent; an old peripheral scar alone is not proof of active infection.

First-line investigation

Targeted IgG/IgM serology with reference-laboratory confirmation when needed; MRI brain for neurological disease; urgent fetal or ophthalmic specialist assessment for pregnancy or visual involvement.

Management

Identify neurological, ocular and pregnancy emergencies

Send confusion, seizure, focal neurology or raised intracranial pressure for emergency imaging and specialist review; send visual loss or floaters for urgent ophthalmology.^2,3,8
Refer suspected infection in pregnancy or a concerning fetal scan urgently to fetal medicine, obstetric infection and the Toxoplasma Reference Laboratory; routine screening is not offered.^4,5,2

Treat the affected compartment

Treat cerebral disease with specialist pyrimethamine plus sulfadiazine and folinic acid, usually for at least 6 weeks, or a specialist alternative; monitor blood counts and organ function.^3,7
Treat active ocular disease with urgent ophthalmology and infectious-diseases input; do not treat an old inactive scar as active disease without clinical evidence.^8,10,7

Protect fetus, infant and immune system

For pregnancy, separate the non-HIV fetal-transmission pathway from the BHIVA HIV-pregnancy pathway; BHIVA recommends pyrimethamine plus sulfadiazine, folinic acid 15 mg daily, no sulfadiazine after week 32 and specialist alternatives.^6,4,7
Review at-risk newborns with paediatric infectious diseases, ophthalmology and neonatology; use the reference-laboratory and current congenital-toxoplasma reporting pathway.^6,9,11
Coordinate ART or adjustment of immunosuppression with the relevant specialist and use current HIV prophylaxis guidance for advanced immunosuppression.^3,2,7

Prevent exposure and monitor sequelae

Cook meat thoroughly, wash produce and kitchen equipment, use gloves for soil, avoid cat faeces and do not feed cats raw meat; arrange long-term eye, neurological and developmental follow-up where indicated.^2,1

Exam traps

A single positive IgM does not prove recent primary infection because IgM may persist; use reference-laboratory interpretation and avidity or repeat testing when indicated.
Multiple ring-enhancing lesions in advanced HIV suggest toxoplasmosis, but primary CNS lymphoma and other infections remain possible; lack of response needs diagnostic escalation.
Always give folinic acid with pyrimethamine to reduce marrow toxicity.
Routine antenatal toxoplasmosis screening is not recommended in the UK.
Pregnancy management is not one universal pathway: BHIVA guidance applies specifically to women living with HIV, while suspected primary infection without HIV requires fetal-medicine and infection-specialist management.
An old chorioretinal scar does not necessarily mean active ocular toxoplasmosis.

Illustrations

Occipital cerebral toxoplasmosis on MRIAxial brain MRI showing a ring-like right occipital lesion with surrounding oedema in cerebral toxoplasmosis in advanced HIV.Jmarchn, Wikimedia Commons · CC-BY-SA-3.0

Key sources

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.