Acanthamoeba Infections

KEY FEATURES

Essentials of Diagnosis

• Acute meningoencephalitis or chronic granulomatous encephalitis after contact with warm fresh water

• Keratitis, particularly in contact lens users

General Considerations

• Free-living amoebas of the genus Acanthamoeba, Naegleria, Balamuthia, and Sappinia

• Found in soil and in fresh, brackish water

Primary amebic meningoencephalitis

• Fulminate, hemorrhagic, necrotizing meningoencephalitis

• Occurs in healthy children and young adults

• Rapidly fatal

Granulomatous amebic encephalitis

• Caused by Acanthamoeba species, Balamuthia mandrillaris, and Sappinia

• More chronic than primary amebic meningoencephalitis

Acanthamoeba keratitis

• Painful, sight-threatening corneal infection

• Associated with corneal trauma, most commonly after use of contact lenses and contaminated saline solution

CLINICAL FINDINGS

Symptoms and Signs

Primary amebic meningoencephalitis

• Incubation period varies from 2 to 15 days

• Early symptoms include

  • Headache, fever, stiff neck, and lethargy

  • Often associated with rhinitis and pharyngitis

• Vomiting, disorientation, and other signs of meningoencephalitis develop within 1 or 2 days

• Coma and death occur within 7–10 days

• Clinical features resemble infection from acute bacterial meningoencephalitis

Granulomatous amebic encephalitis

• Neurologic disease

  • May be preceded by skin lesions, including ulcers and nodules

  • Develops slowly after an uncertain incubation period

  • Headache, meningismus

  • Nausea, vomiting, lethargy

• Low-grade fevers

• Over weeks to months, symptoms progress to

  • Focal neurologic findings

  • Mental status abnormalities

  • Coma and death

Acanthamoeba keratitis

• Progresses slowly, with waxing and waning clinical findings over months; can progress to blindness

• Severe eye pain

• Photophobia

• Tearing

• Blurred vision

Differential Diagnosis

• Many cases of Acanthamoeba keratitis are misdiagnosed as viral keratitis

DIAGNOSIS

Laboratory Tests

Primary amebic meningoencephalitis

• Cerebrospinal fluid (CSF)

  • Contains hundreds to thousands of leukocytes and erythrocytes per cubic millimeter

  • Protein usually elevated; glucose is normal or moderately reduced

  • Fresh wet mount may show motile trophozoites

  • Staining with Giemsa or Wright stain will identify the trophozoites

  • Species identification is based on morphology and immunologic methods

Granulomatous amebic encephalitis

• CSF

  • Shows lymphocytic pleocytosis with elevated protein levels

  • Amoebas not typically seen

• Diagnosis can be made by biopsy of skin or brain lesions

• Lumbar puncture is dangerous due to increased intracranial pressure

Acanthamoeba keratitis

• Lack of response to antibacterial, antifungal, and antiviral topical treatments and potential use of contaminated contact lens solution are suggestive of the diagnosis

• Ocular examination shows corneal ring infiltrates, but these can also be ...