The amebas can enter the brain through the nose when people swim in contaminated warm, fresh water.
Primary amebic meningoencephalitis 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 do a spinal tap to obtain a sample of cerebrospinal fluid and sometimes remove a small piece of brain tissue (biopsy), then examine and analyse the sample obtained.
Determining the best treatment is difficult, but doctors typically use a combination of medications including miltefosine.
(See also Overview of Parasitic Infections Overview of Parasitic Infections A parasite is an organism that lives on or inside another organism (the host) and benefits (for example, by getting nutrients) from the host at the host's expense. Although this definition actually... read more .)
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. Although they rarely cause human infection, certain types of these amebas can cause serious, life-threatening diseases.
Naegleria fowleri, also known as a "brain eating ameba," is present worldwide. In the United States, the majority of infections have occurred in southern states following exposure to warm, fresh water in lakes and rivers in the summer. Naegleria fowleri can also live in hot springs or warm water discharged from industrial plants, poorly maintained swimming pools with minimal or no chlorination, and soil. It can even grow in water heaters at temperatures up to 115° F (46° C) and survive for short periods at higher temperatures. Naegleria does not live in salt water.
When people, usually children or young adults, swim in contaminated water, the amebas can enter the central nervous system through the nose. When they reach the brain, they cause inflammation and tissue destruction, which usually progresses rapidly to death.
Primary amebic meningoencephalitis differs from granulomatous amebic encephalitis Amebic Brain Infection: Granulomatous Amebic Encephalitis read more , which is another very rare, usually fatal infection of the central nervous system caused by different free-living amebas, Acanthamoeba species or Balamuthia mandrillaris. Granulomatous amebic encephalitis usually occurs in people with a weakened immune system Overview of Immunodeficiency Disorders Immunodeficiency disorders involve malfunction of the immune system, resulting in infections that develop and recur more frequently, are more severe, and last longer than usual. Immunodeficiency... read more or generally poor health, and typically progresses more slowly than primary amebic meningoencephalitis.
Symptoms of Primary Amebic Meningoencephalitis
Symptoms of primary amebic meningoencephalitis 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, causing death 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, such as computed tomography Computed Tomography (CT) In computed tomography (CT), which used to be called computed axial tomography (CAT), an x-ray source and x-ray detector rotate around a person. In modern scanners, the x-ray detector usually... read more (CT) and magnetic resonance imaging Magnetic Resonance Imaging (MRI) In magnetic resonance imaging (MRI), a strong magnetic field and very high frequency radio waves are used to produce highly detailed images. MRI does not use x-rays and is usually very safe... read more (MRI), are done to rule out other possible causes of the brain infection, but they cannot confirm that amebas are the cause.
A spinal tap Spinal Tap Diagnostic procedures may be needed to confirm a diagnosis suggested by the medical history and neurologic examination. Electroencephalography (EEG) is a simple, painless procedure in which... read more (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 Introduction to Meningitis Meningitis is inflammation of the layers of tissue that cover the brain and spinal cord (meninges) and of the fluid-filled space between the meninges (subarachnoid space). Meningitis can be... read more and brain infection Overview of Brain Infections Infections of the brain can be caused by viruses, bacteria, fungi, or, occasionally, protozoa or parasites. Another group of brain disorders, called spongiform encephalopathies, are caused by... read more , but doctors are not always able to find the amebas in the sample.
Other techniques are available in specialized laboratories and are more likely to detect the amebas. They include the following:
Culture (growing microorganisms in a laboratory until there are enough to identify)
Polymerase chain reaction (PCR) to check for the genetic material of the ameba
A biopsy of brain tissue that is stained and examined under a microscope 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 including
and one or more of the following:
Amphotericin B (typically used to treat fungal infections—an antifungal medication)
Rifampin (an antibiotic)
Fluconazole or the related medications voriconazole, ketoconazole, or itraconazole (antifungal medications)
Azithromycin (an antibiotic)
Although miltefosine can cause birth defects in pregnant women, doctors often use it anyway because primary amebic encephalitis is usually fatal without treatment, so the potential benefits of therapy outweigh the risk. Women of childbearing age who are taking this medication must use effective birth control measures.
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: Primary Amebic Meningoencephalitis (PAM)