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Amebic Brain Infection: Granulomatous Amebic Encephalitis


Richard D. Pearson

, MD, University of Virginia School of Medicine

Last full review/revision Dec 2020| Content last modified Dec 2020

Granulomatous amebic encephalitis is a very rare, usually fatal infection of the central nervous system caused by Acanthamoeba species or Balamuthia mandrillaris, two types of free-living amebas. It usually occurs in people with a weakened immune system or generally poor health.

  • The amebas probably enter through the skin or lungs and spread to the brain through the bloodstream.
  • Symptoms of granulomatous amebic encephalitis begin gradually and include confusion, headache, blurred vision, seizures, and skin sores.
  • Imaging tests and a spinal tap can help doctors exclude other potential causes. When a skin sore is present, a sample is taken and examined under a microscope to look for amebas. Brain biopsy can also be diagnostic.
  • Doctors typically use a combination of drugs including miltefosine to treat the infection.

(See also Overview of Parasitic Infections.)

Free-living amebas are protozoa that live in soil or water and do not need to live in people or animals. Although they rarely cause human infection, certain types of these amebas can cause serious, life-threatening diseases.

The amebas that cause granulomatous amebic encephalitis live in water, soil, and dust throughout the world. Many people are exposed, but few are infected. Infection usually occurs in people whose immune system is weakened or whose general health is poor, although Balamuthia mandrillaris may infect healthy people.

Amebas probably enter through the skin or lungs and spread to the brain through the bloodstream.

Granulomatous amebic encephalitis differs from primary amebic meningoencephalitis. Primary amebic meningoencephalitis, though also rare, can affect healthy people who swim in fresh water. Primary amebic meningoencephalitis is caused by a free-living ameba called Naegleria fowleri, which is thought to enter the central nervous system through the nose.


Symptoms of granulomatous amebic encephalitis begin gradually. Confusion, headache, and seizures are common. People may have a low-grade fever, blurred vision, changes in personality, and problems with speaking, coordination, or vision. One side of the body or face may become paralyzed.

Balamuthia mandrillaris may cause skin sores in addition to the symptoms above.

Most infected people die, usually 7 to 120 days after symptoms begin.


  • Computed tomography and magnetic resonance imaging of the brain
  • A spinal tap
  • Biopsy of skin sores or lesions in the brain

Computed tomography (CT) and magnetic resonance imaging (MRI) of the brain and a spinal tap (lumbar puncture) are usually done to diagnose granulomatous amebic encephalitis. These tests help exclude other possible causes but usually cannot confirm the diagnosis.

Skin sores typically contain amebas and, if present, are biopsied. Brain biopsy can also be diagnostic.

Granulomatous amebic encephalitis is often diagnosed only after death.


  • A combination of drugs

Granulomatous amebic encephalitis and any skin sores are typically treated with a combination of drugs including

  • Miltefosine

and one or more of the following:

  • Pentamidine (typically used to treat fungal infections—an antifungal drug—or protozoal infections)
  • Sulfadiazine or trimethoprim/sulfamethoxazole (antibiotics)
  • Flucytosine (an antifungal drug)
  • Fluconazole or the related drugs voriconazole or itraconazole (antifungal drugs)
  • Amphotericin B (an antifungal drug)
  • Azithromycin or clarithromycin (antibiotics)

Some of these drugs are taken by mouth, and others are given by injection. Some can be given in more than one way.

Although miltefosine can cause birth defects in pregnant women, doctors often use it anyway because granulomatous amebic encephalitis is usually fatal without treatment, so the potential benefits of therapy outweigh the risk. Women of childbearing age who are taking this drug must use effective birth control measures.

Sometimes surgery is also needed.

Skin sores, if present, are cleaned.

More Information

  • Centers for Disease Control and Prevention: Granulomatous Amebic Encephalitis (GAE)

Drugs Mentioned In This Article

Generic Name Select Brand Names
clarithromycin BIAXIN
Azithromycin ZITHROMAX
voriconazole VFEND
itraconazole SPORANOX
Sulfadiazine No US brand name
Pentamidine NEBUPENT
Fluconazole DIFLUCAN
Flucytosine ANCOBON

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