Amebic Meningoencephalitis, Primary

For further information, see CMDT Part 35-08: Infections with Pathogenic Free-Living Amoebas

Key Features

Essentials of Diagnosis

• A fulminating, hemorrhagic, necrotizing meningoencephalitis

• Occurs in healthy children and young adults and is rapidly fatal

General Considerations

• Caused by free-living amoebae

  • Naegleria fowleri (most commonly)

  • Balamuthia mandrillaris

  • Acanthamoeba species

• The incubation period varies from 2 to 15 days

Demographics

• N fowleri is a thermophilic organism found in

  • Fresh and polluted warm lake water

  • Domestic water supplies

  • Swimming pools

  • Thermal water

  • Sewers

• Most patients give a history of exposure to warm fresh water

Clinical Findings

Symptoms and Signs

• 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, followed by coma and then death within 7–10 days

Differential Diagnosis

• No distinctive clinical features distinguish the infection from acute bacterial meningoencephalitis

Diagnosis

Laboratory Tests

• Cerebrospinal fluid (CSF) shows hundred to thousands of leukocytes and erythrocytes per cubic millimeter

• Protein is usually elevated, and glucose is normal or moderately reduced

• A fresh wet mount of the CSF may show motile trophozoites

• Staining with Giemsa or Wright stain will identify trophozoites

• Species identification is based on morphology and immunologic methods

Treatment

Medications

• Amphotericin B is drug of choice

• Four survivors in North America were treated with amphotericin B, rifampin, and other agents

Outcome

Prognosis

• Nearly always fatal

When to Admit

• All patients with confirmed or suspected disease

References