Toxoplasmosis

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

Diagnosis

• Serologic tests are the primary means of ...