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

Granulomatous amebic encephalitis

• Caused by Acanthamoeba species, Balamuthia mandrillaris, and Sappinia

• More chronic than primary amebic meningoencephalitis (see Amebic Meningoencephalitis, Primary)

• Neurologic disease

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

  • Develops slowly after an uncertain incubation period

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

Granulomatous amebic encephalitis

• Headache

• Meningismus

• Nausea, vomiting

• Lethargy

• Low-grade fevers

• Focal neurologic findings, mental status abnormalities

Keratitis

• Progresses slowly, with waxing and waning clinical findings over months

• Severe eye pain

• Photophobia

• Tearing

• Blurred vision

Differential Diagnosis

• Many cases of Acanthamoeba keratitis are misdiagnosed as viral keratitis

Diagnosis

Laboratory Tests

Granulomatous amebic encephalitis

• Cerebrospinal fluid

  • 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

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 caused by other pathogens

• Diagnosis can be made by examination or culture of corneal scrapings

• Available diagnostic techniques include

  • Examination of a wet preparation for cysts and motile trophozoites

  • Examination of stained specimens

  • Evaluation with immunofluorescent reagents, culture of organisms, and polymerase chain reaction

Imaging Studies

• CT and MRI show single or multiple nonspecific lesions in patients with encephalitis

Treatment

Medications

Granulomatous amebic encephalitis

• Some patients have been treated successfully with various combinations of

  • Flucytosine

  • Pentamidine

  • Fluconazole or itraconazole

  • Sulfadiazine

  • Trimethoprim-sulfamethoxazole

  • Azithromycin

• However, no treatment has been proved effective

Keratitis

• Can be cured with local therapy

• Topical propamidine isethionate (0.1%), chlorhexidine digluconate (0.02%), polyhexamethylene biguanide, neomycin-polymyxin B-gramicidin, miconazole, and combinations of these agents have been used successfully

• Oral itraconazole or ketoconazole can be ...