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Key Features

Essentials of Diagnosis

  • Congenital toxoplasmosis: chorioretinitis, microphthalmia, strabismus, microcephaly, hydrocephaly, convulsions, psychomotor retardation, intracranial calcifications, jaundice, hepatosplenomegaly, abnormal blood cell counts

  • Acquired toxoplasmosis in an immunocompetent patient: lymphadenopathy, hepatosplenomegaly, rash

  • Acquired or reactivated toxoplasmosis in an immunocompromised patient: encephalitis, chorioretinitis, myocarditis, and pneumonitis

  • Ocular toxoplasmosis: chorioretinitis

  • Serologic evidence of infection with Toxoplasma gondii or demonstration of the agent in tissue or body fluids

General Considerations

  • The two major routes of Toxoplasma transmission to humans are oral and congenital

  • Oral infection occurs after ingestion of cysts from food, water, or soil contaminated with cat feces or from ingestion of undercooked meat or other food products that contain cysts

  • Oocysts survive up to 18 months in moist soil but is limited in dry, very cold, or very hot conditions and at high altitude

  • In the United States, less than 1% of cattle and 25% of sheep and pigs are infected with toxoplasmosis

  • In humans, depending on geographic area, seropositivity increases with age from 0 to 10% in children younger than 10 years to 3–70% in adults

Clinical Findings

  • Congenital toxoplasmosis

    • Occurs in 1 in 3000 to 10,000 live births in the United States

    • Clinical disease is severe

      • Microcephaly or hydrocephaly

      • Severe chorioretinitis

      • Hearing loss

      • Convulsions

      • Abnormal cerebrospinal fluid (CSF) (xanthochromia and mononuclear pleocytosis)

      • Cerebral calcifications

      • Mental retardation

    • Other findings

      • Strabismus

      • Eye palsy

      • Maculopapular rash

      • Pneumonitis

      • Myocarditis

      • Hepatosplenomegaly

      • Jaundice

      • Thrombocytopenia

      • Lymphocytosis and monocytosis

      • Erythroblastosis-like syndrome

  • Acquired Toxoplasma infection in the immunocompetent patient

    • Usually asymptomatic

    • An infectious mononucleosis-like syndrome with lymphadenopathy and/or a flu-like illness develops in about 10–20% of patients

    • Nodes are discrete, variably tender, and do not suppurate

    • Cervical lymph nodes are most frequently involved, but any nodes may be enlarged

    • Less common findings

      • Fever

      • Malaise

      • Myalgias

      • Fatigue

      • Hepatosplenomegaly

      • Lymphopenia (usually < 10%)

      • Liver enzyme elevations

    • Unilateral chorioretinitis may occur

  • Acute toxoplasmosis in the immunodeficient patient

    • Patients infected with HIV, and those with lymphoma, leukemia, or transplantation, are at high risk for developing severe disease (most commonly central nervous system [CNS] disease, but also chorioretinitis, myocarditis, or pneumonitis) following acute infection or reactivation

    • Toxoplasmic encephalitis is a common cause of mass lesions in the brains of persons with HIV/AIDS

  • Ocular toxoplasmosis

    • Presents as a focal necrotizing retinochoroiditis often associated with a preexistent chorioretinal scar, and variable involvement of the vitreous, retinal blood vessels, optic nerve, and anterior segment of the eye

    • Appearance of the ocular lesion is not specific and mimics other granulomatous ocular diseases

Differential Diagnosis

  • Congenital toxoplasmosis must be differentiated from

    • Infection with cytomegalovirus, rubella, herpes simplex, syphilis

    • Listeriosis

    • Erythroblastosis

    • Encephalopathies that accompany degenerative diseases

  • Acquired infection can mimic viral, bacterial, or lymphoproliferative disorders

  • Ocular toxoplasmosis can mimic other infectious, noninfectious, and neoplastic ocular conditions


  • Serologic tests are the primary means of ...

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