Acute Toxoplasmosis

Acute toxoplasmosis is primary or reactivated infection by Toxoplasma gondii, producing asymptomatic or mild disease in the immunocompetent and life threatening organ disease in the immunocompromised. Congenital transmission follows primary infection in pregnancy.

• Sources: undercooked pork, lamb and goat meat, oocysts in soil or cat faeces, contaminated water, transplanted organs.
• Reactivation of bradyzoite cysts occurs when CD4 falls below 100 cells/mm3 in HIV.

Immunocompetent: asymptomatic or lymphadenopathy, fever, fatigue, myalgia; ocular toxoplasmosis presents with floaters and blurred vision from necrotising retinochoroiditis.

• Immunocompromised: cerebral toxoplasmosis with headache, fever, confusion, focal deficits, seizures; pneumonitis; myocarditis; disseminated disease.
• Congenital: hydrocephalus, intracranial calcification, chorioretinitis, seizures, jaundice, hepatosplenomegaly, stillbirth.
• Differential diagnosis: cerebral lymphoma, tuberculoma, cryptococcal disease, progressive multifocal leucoencephalopathy, brain abscess, neurocysticercosis, CMV, HIV encephalopathy.
• Complications: encephalitis with mass lesions, seizures, vision loss, congenital disease, relapse, death.

Serology, imaging and PCR.

• IgG and IgM with IgG avidity; PCR on blood, CSF, amniotic fluid; in HIV, positive Toxoplasma IgG with a typical ring enhancing multiple lesions on CT or MRI strongly suggests cerebral toxoplasmosis.
• Fundoscopy: focal necrotising retinitis next to old pigmented scars.
• HIV test and CD4; biopsy only when empirical therapy fails at 10 to 14 days.
• Fetal ultrasound and amniotic fluid PCR from 18 weeks; neonatal serology, eye and brain imaging.

Treat symptomatic, ocular, congenital and immunocompromised disease.

• Supportive: bed rest, seizure precautions, nutrition, intracranial pressure care, avoid undercooked meat, wash produce, hand hygiene, avoid cat litter in pregnancy.
• Pharmacological, cerebral toxoplasmosis: pyrimethamine 200 mg loading dose then 50 mg daily (75 mg for 60 kg and over) with sulfadiazine 1 g four times daily (1.5 g for 60 kg and over) and folinic acid 10 to 25 mg daily for at least 6 weeks; alternative cotrimoxazole (trimethoprim 5 mg/kg with sulfamethoxazole 25 mg/kg) twice daily orally or IV; or clindamycin 600 mg four times daily with pyrimethamine and folinic acid. Dexamethasone 4 mg four times daily only for marked oedema or mass effect, with quick taper. Levetiracetam 500 mg twice daily for seizures. Maintenance: pyrimethamine 25 mg daily with sulfadiazine 500 mg four times daily and folinic acid 10 mg daily (or cotrimoxazole 960 mg daily) until CD4 is over 200 for 6 months. Start antiretroviral therapy within 2 weeks. Ocular toxoplasmosis: pyrimethamine 50 mg daily with sulfadiazine 1 g four times daily and folinic acid 10 mg daily for 4 to 6 weeks, with prednisolone 40 mg daily started 2 days later and tapered. Pregnancy: spiramycin 1 g three times daily until delivery if fetus uninfected; if fetus is infected after 18 weeks, pyrimethamine 50 mg daily with sulfadiazine 3 g daily and folinic acid 10 to 25 mg daily. Congenital: pyrimethamine, sulfadiazine and folinic acid for 12 months under paediatric specialist care.
• Procedures: stereotactic biopsy if no response in 10 to 14 days; ventriculoperitoneal shunt for hydrocephalus.
• Special groups: pregnancy, spiramycin or the combination after 18 weeks with monthly blood counts; infants, specialist therapy; sulfa allergy, desensitise or use clindamycin; renal impairment, adjust sulfadiazine and give fluids.
• Red flags: new focal deficit, seizures, reduced consciousness, visual loss, bone marrow suppression, rash on sulfadiazine, crystalluria.
• Follow-up: clinical and imaging review at 2 weeks and 6 weeks; weekly blood counts on pyrimethamine; visual and developmental surveillance for infants.