Primary amebic meningoencephalitis is a rare, usually fatal infection of the brain caused by the free-living ameba Naegleria fowleri.
The ameba can enter the brain through the nose when people swim in contaminated, warm fresh water.
Symptoms can progress rapidly from changes in smell or taste, headaches, a stiff neck, nausea, and vomiting to confusion and death.
To check for amebas, doctors perform a spinal tap to obtain a sample of cerebrospinal fluid and sometimes remove a small piece of brain tissue (biopsy), then examine and analyze the sample obtained.
Determining the best treatment is difficult, but doctors typically use a combination of medications including miltefosine.Determining the best treatment is difficult, but doctors typically use a combination of medications including miltefosine.
Free-living amebas are protozoa, which is a type of parasite. They make up a diverse group of microscopic, one-celled organisms. Although they rarely cause infections in people, certain types of these amebas can cause serious, life-threatening infections.
The free-living ameba Naegleria fowleri is further categorized as an extraintestinal protozoan (see also Introduction to Extraintestinal Protozoa), which means it causes infections only in areas outside of the intestines such as the brain.
Free-living amebas are protozoa (single-cell infectious organisms) that live in soil or water and do not need to live in people or animals.
Naegleria fowleri, also commonly known as the "brain-eating ameba," is present worldwide in soil and in bodies of warm, fresh water. This ameba can also live in hot springs, warm water that is discharged from industrial plants, or in poorly maintained swimming pools with minimal or no chlorination. It can even grow in water heaters at temperatures up to 115° F (46° C) and survive for short periods at higher temperatures. Naegleria fowleri does not live in salt water.
In the United States, the majority of people are infected in southern states after swimming or diving into contaminated, warm, fresh-water lakes and rivers in the summer.
This ameba does not need a human or animal host to live, but it can enter through the nose and spread to the brain. When they reach the brain, they cause inflammation and tissue destruction, which usually progresses rapidly to death. Most infected people are healthy children or young adults.
Primary amebic meningoencephalitis differs from granulomatous amebic encephalitis, which is another very rare, usually fatal infection of the central nervous system caused by different free-living amebas, Acanthamoeba species, Sappinia pedata, or Balamuthia mandrillaris. Granulomatous amebic encephalitis usually occurs in people with a weakened immune system or generally poor health, and typically progresses more slowly than primary amebic meningoencephalitis.
(See also Overview of Parasitic Infections.)
Symptoms of Primary Amebic Meningoencephalitis
Symptoms begin within 1 to 2 weeks of exposure to contaminated water. Sometimes the first symptom is a change in smell or taste. Later, people have a headache, a stiff neck, sensitivity to light, nausea, and vomiting. They may become confused and sleepy and may have seizures.
The infection can progress rapidly and may be fatal within 10 days.
Diagnosis of Primary Amebic Meningoencephalitis
A spinal tap and analysis of cerebrospinal fluid
Doctors suspect primary amebic meningoencephalitis in people who have symptoms and have been swimming recently in fresh water, but the diagnosis is difficult to confirm. Imaging tests of the brain, such as computed tomography (CT) and magnetic resonance imaging (MRI), are done to rule out other possible causes of the infection, but they cannot confirm that an ameba is the cause.
A spinal tap (lumbar puncture) is done to obtain a sample of cerebrospinal fluid (the fluid that surrounds the brain and spinal cord). This test can exclude some other possible causes of meningitis and brain infection, but doctors are not always able to find the amebas in the sample.
Other testing techniques are available in specialized laboratories and are more likely to detect the ameba:
Culture (allows doctors to grow the ameba in a laboratory until there are enough to identify)
Polymerase chain reaction (PCR) testing to check for the genetic material (DNA) of the ameba
Removal of a sample of brain tissue that is examined under a microscope (biopsy) or analyzed using PCR
Treatment of Primary Amebic Meningoencephalitis
A combination of medications
Because few people survive, determining the best treatment for primary amebic meningoencephalitis is difficult.
Doctors typically use a combination of several medications to treat people who have the infection.
The medication miltefosine is given to all people who have primary amebic meningoencephalitis. Miltefosine is given in combination with 1 or more of the following medications: is given to all people who have primary amebic meningoencephalitis. Miltefosine is given in combination with 1 or more of the following medications:
Amphotericin BAmphotericin B
RifampinRifampin
Fluconazole, voriconazole, or ketoconazoleFluconazole, voriconazole, or ketoconazole
Azithromycin or minocyclineAzithromycin or minocycline
Although miltefosine can cause birth defects in a fetus, doctors may give it to infected pregnant people anyway because primary amebic meningoencephalitis is usually fatal without treatment, so the potential benefits of therapy outweigh the risks to the fetus.
Doctors may prescribe nitroxoline, an experimental medication, that is usually used in combination with other medications.
Other medications are often given to control seizures and swelling of the brain. People may be placed on a special cooling blanket for a few days to lower their body temperature to below normal. This treatment is known as therapeutic hypothermia. Therapeutic hypothermia helps lessen or prevent further injury to the brain.
More Information
The following English-language resource may be useful. Please note that The Manual is not responsible for the content of this resource.
Centers for Disease Control and Prevention (CDC): About Naegleria fowleri Infections
Drugs Mentioned In This Article
