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IDCU HomeInfectious Diseases A-C
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Infectious Disease Control Unit
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Home >
Infectious Disease Control >
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Amebic Central Nervous System (CNS) Infections
Amebic Central Nervous System (CNS)
Infections
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Resources
Disease Condition
Primary Amebic Meningoencephalitis and Other Amebic Meningitis/Encephalitis
Organism
Primary Amebic Meningoencephalitis (PAM) is caused by an ameba called Naegleria
fowleri. Granulomatous Amebic Encephalitis (GAE) is caused by Balamuthia
mandrillaris or by Acanthamoeba species, including A. culbertsoni, A. polyphaga, A.
castellanii, A. astronyxis, A. hatchetti, A. rhysodes, A. divionensis, A. lugdunensis, A.
lenticulata, and A. haelyi. Other central nervous system (CNS) infections may be caused
by other amebae such as Sappinia species (including S. diploidea and S. pedata).
Transmission
Amebic meningitis/encephalitis infections are not spread from person to person. The
amebae that cause amebic meningitis/encephalitis enter the body through different routes,
depending on the specific ameba:
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Naegleria fowleri infects people when water containing the ameba enters the body through the
nose. This typically occurs when people go swimming or diving in warm freshwater places, like
lakes and rivers. In very rare instances, Naegleria infections may also occur when contaminated
water from other sources (such as inadequately chlorinated swimming pool water or contaminated
tap water) enters the nose, such as when people submerge their heads or cleanse their noses
during religious practices, and when people irrigate their sinuses (nose) using contaminated tap
water. The Naegleria fowleri ameba then travels up the nose to the brain where it destroys the
brain tissue. Naegleria fowleri has not been shown to spread via water vapor or aerosol droplets
(such as shower mist or vapor from a humidifier), and you cannot be infected with Naegleria
fowleri by drinking contaminated water.
While infections with Naegleria fowleri are rare, they occur mainly during the summer
months of July, August, and September. Infections are more likely to occur in southerntier states. Infections usually occur when it is hot for prolonged periods of time, which
results in higher water temperatures and lower water levels.
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Balamuthia is thought to enter the body when soil containing Balamuthia comes in
contact with skin wounds and cuts, or when dust containing Balamuthia is
breathed in or gets in the mouth. Once inside the body, the amebae can travel
through the blood stream to the brain, where they cause GAE. There are also a few
reports of dogs that might have become infected after swimming in ponds.
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Acanthamoeba can enter the skin through a cut or wound, or through the nostrils.
Once inside the body, the amebae travel through the bloodstream to other parts of
the body, especially the lungs, brain, and spinal cord.
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Sappinia may enter the body through the nose or via cuts and bruises on the body.
In the only known case, the patient had signs of a sinus infection before
developing symptoms of amebic encephalitis.
Symptoms
The symptoms of amebic meningitis/encephalitis vary depending on the infecting ameba:
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Primary Amebic Meningoencephalitis (PAM)/Naegleria fowleri: In its early
stages, symptoms of PAM may be similar to symptoms of bacterial meningitis.
Initial symptoms of PAM start about 5 days (range 1 to 7 days) after infection. The
initial symptoms may include headache, fever, nausea, or vomiting. Later
symptoms can include stiff neck, confusion, lack of attention to people and
surroundings, loss of balance, seizures, and hallucinations. After the start of
symptoms, the disease progresses rapidly and usually causes death within about 5
days (range: 1 to 12 days).
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Granulomatous Amebic Encephalitis (GAE)/Balamuthia mandrillaris: The
infection can begin with a skin wound on the face, chest, torso, arms, or legs. If the
infection involves the brain, the disease it causes is called GAE. Diagnosis of
Balamuthia GAE can be difficult, but some early symptoms might include:
o Headaches
o Stiff neck or head and neck pain with neck movement
o Sensitivity to light
o Nausea
o Vomiting
o Lethargy (tiredness)
o Low-grade fever
Other signs of Balamuthia GAE might include:
o
o
Behavioral changes
o Seizures
o Weight loss
o Partial paralysis
Difficulty speaking in full sentences
o Difficulty walking
The disease might appear mild at first but can become more severe over
weeks to several months. Often the disease is fatal, with a death rate of
more than 95%. Early diagnosis and treatment may increase the chances for
survival.
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Granulomatous Amebic Encephalitis (GAE)/Acanthamoeba
species: This is a serious, most often deadly, infection of the brain
and spinal cord. Once infected, a person may suffer with headaches,
stiff neck, nausea and vomiting, tiredness, confusion, lack of
attention to people and surroundings, loss of balance and bodily
control, seizures, and hallucinations. Symptoms progress over
several weeks and death usually occurs.
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Amebic encephalitis/Sappinia species: There is only one known
case of Sappinia encephalitis in a human. Symptoms of Sappinia
infection may include:
o Headache
o Sensitivity to light
o Nausea or upset stomach
o Vomiting
o Blurry vision
o Loss of consciousness
A scan of the one known infected patient’s brain also revealed a 2centimeter tumor-like mass on the back left section of his brain.
Some groups have a higher risk of infection or disease:
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Primary Amebic Meningoencephalitis: PAM disproportionately
affects males and children. The reason for this distribution pattern is
unclear but may reflect the types of water activities (such as diving
or watersports) that might be more common among young boys.
The extremely low occurrence of PAM makes epidemiologic study
difficult.
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Granulomatous Amebic Encephalitis: Balamuthia infection can
occur in anyone. GAE or disseminated infection caused by
Acanthamoeba occurs more frequently in people with compromised
immune systems or those who are chronically ill.
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Amebic encephalitis caused by Sappinia species: Sappinia can
infect anyone. However, individuals with weakened immune
systems and people who have contact with animal feces are at a
higher risk for infection.
Prevention
Primary Amebic Meningoencephalitis:
Although infections are severe, the risk of Naegleria fowleri infection is very low. There
have been 30 reported infections in the U.S. during the 10 years from 2000-2009, despite
millions of recreational water exposures each year. By comparison, during the ten years
from 1996 to 2005, there were over 36,000 drowning deaths in the U.S. It is likely that a
low risk of Naegleria fowleri infection will always exist with recreational use of warm
freshwater lakes, rivers, and hot springs. The low number of infections makes it difficult
to know why some people have been infected compared to the millions of other people
using the same or similar waters across the U.S. The only way to prevent Naegleria
fowleri infection is to refrain from water-related activities. If you do plan to take part in
water-related activities, here are some measures that might reduce risk:
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Avoid water-related activities in bodies of warm freshwater during periods of high
water temperature and low water levels.
 Hold the nose shut or use nose clips when taking part in water-related activities in
bodies of warm freshwater such as lakes, rivers, or hot springs.
 Avoid digging in or stirring up the sediment while taking part in water-related
activities in shallow, warm, freshwater areas.
 If you use a Neti-Pot or syringe for nasal irrigation or sinus flushes be sure to use
only sterile, distilled, or lukewarm previously boiled water.
Granulomatous Amebic Encephalitis:
Currently, there are no known ways to prevent infection with Balamuthia or
Acanthamoeba. Since persons with weakened immune systems are more susceptible to
Acanthamoeba infection, they should follow the advice of their treating physician
carefully.
Recent Texas Trends
Primary Amebic Meningoencephalitis (PAM)/Naegleria fowleri:
Since 1972, there have been 34 cases of PAM reported to the Texas Department of State
Health Services (DSHS), just under one case per year. The most recent case of PAM was
reported during August 2013 in a child less than 10 years of age. The median age of PAM
cases reported during this period was 9 years (range: 3 years to 37 years); 76% of casespatients were male. Cases have occurred from May through November, with most cases
occurring in August. Most case-patients reported recent exposure to freshwater lakes,
ponds, and rivers during the warm summer months. No Texas cases have been linked to
nasal irrigation or sinus flushes.
Other Amebic Meningitis and Encephalitis including Granulomatous Amebic Encephalitis
(GAE):
There have been eight other amebic meningitis/encephalitis cases reported to DSHS since
1986, six caused by Balamuthia mandrillaris, one caused by an Acanthamoeba species,
and one by a Sappinia species. Texas’ 1998 Sappinia pedata encephalitis case is the only
known case of amebic encephalitis caused by Sappinia, worldwide. In 2012, Texas
confirmed a case of Acanthamoeba healyi, a species not previously reported to cause
human amebic encephalitis. The most recent Texas case of GAE became ill in June 2014.
Although GAE infections and other amebic meningitis and encephalitis cases have always
been reportable to Texas health departments as exotic diseases, before 2012, PAM was the
only amebic infection of the central nervous system that was listed on the Texas Notifiable
Conditions list.
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Last updated October 19, 2015
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