Toxoplasmosis

(There are further details in the Protozoa chapter of the Part 1 package)

• Obligate intracellular parasite (toxoplasma gondii)

• More common in americas, caribbean, tropical africa

• Contracted by drinking infected water, eating raw meat, or transplacentally (congenital toxo)

• Cats are the definitive host

• Oocysts excreted in cat faeces and ingested

• These become encysted or proliferate

• Toxoplasmosis is the most common cause of posterior uveitis

Clinical features

• 40% develop ocular disease
• Asymptomatic
• Floaters
• Reduced vision
• Vitritis
• Retinitis: active white fluffy areas, progress to circumscribed, pigmented, atrophic scars
  • Satellite lesions near old scars
  • Retinal vasculitis
  • Punctate outer retinitis with quiet vitreous
  • Neuroretinitis

• Anterior uveitis with raised IOP
• Scleritis
• Endophthalmitis-like presentation
• Serous retinal detachments
• Choroidal neovascular membrane
• Congenital toxo: hydrocephalus, cerebral calcification, hepatosplenomegaly, retinochoroiditis

Tests

• Diagnosis is mostly clinical
• Interpret serology with caution: many people will be positive for anti-toxoplasma IgG
• IgM antibodies suggest acquired infection
• Negative serology is helpful to exclude the diagnosis
• AC/vitreous tap can identify T. gondii DNA
• VDRL to exclude syphilis, ACE/CXR to exclude sarcoidosis and HIV serology

Indications for treatment

• Lesions involving disc, macula, papillomacular bundle
• Lesions threatening major vessel
• Marked vitritis
• Immunocompromised patient

Management

• In immunocompetent: Cochrane review showed no evidence for routine antibiotic or steroid in acute retinochoroiditis
• Long-term prophylactic treatment may reduce recurrences
  • Atovaquone

General treatment plans

• Given for at least 4 weeks

• Prednisolone (not if immunocompromised)

• Co-trimoxazole or clindamycin/sulfadiazine or pyrimethamine/sulfadiazine/folinic acid or atovaquone

• Spiramycin for maternal infection in pregnancy to reduce transplacental spread

  • 15-60% risk of transplacental transmission if acquired during pregnancy

• Intravitreal clindamycin and dexamethasone can also be tried

Dosages

• Co-trimoxazole: 960mg twice daily
• Clindamycin: 300mg four times daily
• Pyrimethamine (a folic acid antagonist): 100mg loading dose for one day then 25-50mg per day
• Sulfadiazine: 2-4grams daily for 2 days, then 500mg-1gram four times daily
• Folinic acid: 5-25mg daily alongside pyrimethamine
• Prednisolone 40-60mg daily

Prognosis

• Self-limiting in immunocompetent patients
• Recurrence is common

Advice in pregnancy

• Wash all fruit/vegetables
• Avoid unpasteurised goat’s milk
• Cook meat thoroughly
• Avoid cat litter