Toxoplasmosis is a disease provoked by the obligate intracellular protozoan Toxoplasma gondii. It is found in a variety of mammal and bird hosts. The most common intermediate host is the cat. It is one of the most frequent causes of retinochoroiditis in humans, with more than 60 percent of the United States population and up to 75 percent of the world's general population possessing some seropositive findings

Etiology

• Human infection may occur from ingestion of contaminated or undercooked meat and dairy products, direct or indirect ingestion of cat feces and transplacental transmission from an infected mother to the fetus. Toxoplasmosis can only be transmitted to a fetus during maternal parastemia. Congenital toxoplasmosis accounts for the majority of cases encountered in clinical practice.
• In most cases, the body is primed for infection or toxoplasmosis reactivation by an immune system failure. This may occur following contraction of human immunodeficiency syndrome (HIV) or with medical immunosupression following organ transplantation.

          

Ophthalmic Features

• The symptoms associated with ocular toxoplasmosis include unilateral, mild ocular pain, blurred vision and new onset of floating spots. Patients often describe their vision as hazy.
• Clinical findings may include granulomatous iritis, vitritis, optic disc swelling, neuroretinitis, vasculitis and retinal vein occlusion in the vicinity of the inflammation, in the actively involved eye.
• Funduscopically, active toxoplasmosis presents with white-yellow, choreoretinal lesions and vitreous cells. There may be old, inactive lesions in the fellow eye.
• Toxoplasmosis can produce cystoid macular edema and choroidal neovascularization.

Treatment

• The goal of management is twofold: (1) eradicate the parasite and (2) suppress the inflammatory response.
• Alternative antibiotic treatments include: (1) clindamycin, 300mg, PO QID used with sulfadiazine, for four to six weeks, (2) tetracycline, 2g loading then 250mg PO QID and sulfadiazine for four to six weeks, or (3) trimethoprim/sulfamethoxazole 160/800mg, one tablet PO BID, with or without clindamycin or prednisone, for the same duration.
• In otherwise normal individuals, after beginning antibiotic therapy, add oral steroids at a dose of 20 to 80mg PO daily for four to six weeks. Periocular steroids are never indicated. Oral steroids without systemic antibiotics are expressly contraindicated.