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Amebic Central Nervous System (CNS) Infections

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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:

  • 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 southern-tier states. Infections usually occur when it is hot for prolonged periods of time, which results in higher water temperatures and lower water levels.

  • 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. Finally, there have been reports of Balamuthia transmission to organ transplant recipients from infected donors.
  • 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.
  • 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:

  • 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).
  • 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:
      • Headaches
      • Stiff neck or head and neck pain with neck movement
      • Sensitivity to light
      • Nausea
      • Vomiting
      • Lethargy (tiredness)
      • Low-grade fever
    • Other signs of Balamuthia GAE might include:
      • Behavioral changes
      • Seizures
      • Weight loss
      • Partial paralysis
      • Difficulty speaking in full sentences
      • 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.

  • 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. 
  • Amebic encephalitis/Sappinia species: There is only one known case of Sappinia encephalitis in a human. Symptoms of Sappinia infection may include:
    • Headache
    • Sensitivity to light
    • Nausea or upset stomach
    • Vomiting
    • Blurry vision
    • Loss of consciousness

A scan of the one known infected patient’s brain also revealed a 2-centimeter tumor-like mass on the back left section of his brain.

Some groups have a higher risk of infection or disease:

  • 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.
  • 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.
  • 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:

  • 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. 
  • Use only sterile, distilled, or lukewarm previously boiled water for nasal irrigation or sinus flushes (e.g., Neti Pot usage, ritual nasal ablution, etc.).

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.  

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Other Amebic Meningitis and Encephalitis including Granulomatous Amebic Encephalitis (GAE):

From 1972-2015, 11 other amebic meningitis/encephalitis cases were reported to DSHS, eight caused by Balamuthia mandrillaris, two caused by 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. 

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.




Last updated February 27, 2017