Disease: Naegleria fowleri Infection
(Brain-Eating Amoeba Infection)

    Naegleria fowleri (brain-eating amoeba) infection facts

    • Naegleria fowleri is an amoeba that lives predominately in warm freshwater.
    • Naegleria fowleri is acquired by people when infected water is forcibly aspirated into the nose. This can occur through recreational swimming, diving, or during sports like water skiing.
    • Once acquired, the amoeba travels into the brain, causing primary amoebic meningoencephalitis (PAM). In the popular press, Naegleria fowleri is sometimes called the
      "brain-eating amoeba," and meningoencephalitis is sometimes referred to as Naegleriasis.
    • PAM is very rare, and there are only a few cases reported each year in the United States.
    • People with PAM have a rapidly progressive illness with fever, headache, and stiff neck, and finally coma and death.
    • Infection is diagnosed by examining spinal fluid under the microscope to identify the amoeba. Naegleria fowleri may also be grown in the laboratory, although this takes several days. Newer tests based on PCR technology have been developed but are not widely available.
    • The treatment of choice is an intravenous drug called amphotericin B. Amphotericin B may also be instilled directly into the brain. Because treatment with amphotericin B alone usually fails, other drugs are often added. Miltefosine is a drug that has shown promise, and it is available through the Centers for Disease Control and Prevention. Treatment should be initiated as rapidly as possible, and immediate consultation with an infectious-diseases expert is highly recommended.
    • More than 99% of cases of PAM are fatal despite treatment.

    What is Naegleria fowleri?

    Naegleria fowleri is an amoeba that lives in freshwater and soil. The organism goes through three stages in its life cycle: cysts, flagellates, and trophozoites. Cysts are highly stable in the environment and can withstand near-freezing temperatures. The flagellate form is an intermediate stage that does not consume nutrients or reproduce. The trophozoite form causes human disease. Naegleria are "thermophilic," meaning that they prefer warmer water. Thus, Naegleria infection is found both in tropical and temperate climates. The organism is commonly identified in freshwater, including rivers, lakes, and ponds, or in soil near these sources. Where the water temperature is cool, Naegleria may be found in the sediment at the bottom of lakes or in localized areas where warmer water is discharged into lakes. Naegleria fowleri does not exist in saltwater and is not found in the ocean.

    Although there are many species of Naegleria, only Naegleria fowleri causes human infection. There are other free-living amoebas that cause human disease, including Acanthamoeba.

    What causes a Naegleria fowleri infection?

    N. fowleri infection is a water-borne disease. Exposure occurs when people come into contact with warm freshwater usually through swimming, diving, water skiing, or other recreational activity. Although contact with infected water is common in the United States, symptomatic disease caused by N. fowleri is rare.

    The danger of serious infection comes when water containing Naegleria fowleri is forced into the nose. The amoeba then migrates through the olfactory nerves and enters the brain. The initial exposure can occur when diving or inadvertently aspirating water during swimming. Rarely, underchlorinated swimming pools have been implicated in transmission. Because Naegleria fowleri can be present in untreated well water, there is a small but real chance of transmission to young children during bathing. Naegleria fowleri has also caused disease in adults who inject water into the nose as part of ritual ablutions related to religious practices or as an irrigating solution for sinus passages.

    What are risk factors for Naegleria fowleri infection?

    The source of nearly all of the 128 Naegleria fowleri infections reported since 1962 in the U.S. has been exposure to warm freshwater. These include freshwater lakes and rivers, particularly in Texas and Florida. More than one-quarter of all cases are reported from Florida and most cases have occurred in the South, although recent cases have been reported from Minnesota, from Lake Havasu City in Arizona, from Los Angeles in California, and other sites. Other freshwater sources have included hot springs, poorly chlorinated pools, untreated well water, water heaters, neti pots, and warm water discharge from power plants. Of the 31 cases reported from 2003 to 2012, 28 people acquired the disease from recreational exposure to freshwater and three people acquired it from irrigating their nose with contaminated tap water. There is a decided summertime predominance of cases, and even lakes in the southern States have higher levels of this microbe commonly during the warmer months.

    More than 75% of cases since 1962 were in children or adolescents, and 75% or more were in males. It is known that exposure of the olfactory nerve to contaminated water is the portal of entry to the brain. This exposure often results from water being forcefully introduced into the nose during trauma such as dunking, diving, or crashing while water skiing.

    Hundreds of millions of people go to swimming venues where N. fowleri is found, but fortunately very few become infected. We are unable to calculate an accurate estimate of the true risk of invasive Naegleria fowleri infection.

    What are symptoms and signs of a Naegleria fowleri infection?

    After entering the nose, the amoeba travels into the brain along the olfactory nerve and through membranes to enter the brain. Once in the brain, it causes primary amoebic meningoencephalitis (meaning inflammation of the brain and the lining around the brain), sometimes abbreviated as PAM.

    After exposure to the offending water source, there is generally a two-stage illness. A person infected with Naegleria fowleri will usually develop stage 1 symptoms within two to seven days of exposure.

    Stage 1 signs and symptoms include:

    • severe frontal headache,
    • fever,
    • nausea,
    • vomiting.

    Stage 2 usually begins one to 12 days after stage 1 and may include:

    • stiff neck,
    • seizures,
    • altered mental status,
    • hallucinations,
    • coma.

    The infection progresses so quickly that many people are not diagnosed until after death.

    How is a Naegleria fowleri infection diagnosed?

    Naegleria fowleri should be suspected in people, especially children, with exposure to freshwater who have symptoms of meningitis or meningoencephalitis listed above. The characteristics of the presentation may be nonspecific at first, leading clinicians to suspect more common diseases such as bacterial or viral meningitis. Routine tests may show a high blood white cell count and images of the brain may show inflammation, but neither of these are specific to PAM. A spinal tap will be done and the spinal fluid often shows elevated levels or white cells and red cells. Routine staining (Gram staining) does not detect the amoeba. Thus, it is important to do a wet mount to look for the motile amoeba under the microscope.

    Definitive tests for N. fowleri infection are done in only a few labs in the country. They use one of the following three methods:

    1. N. fowleri nucleic acid tests in CSF or biopsy tissue using PCR
    2. N. fowleri antigen tests in CSF or biopsy tissue using immunohistochemistry (IHC)
    3. It is also possible to culture N. fowleri, but this must be done in the presence of bacteria and at higher temperatures, which is not routinely done in most laboratories.

    What is the treatment for a Naegleria fowleri infection?

    Because Naegleria meningoencephalitis is rare, there are no studies comparing one treatment regimen to another.

    The treatment of choice is amphotericin B, which is an intravenous drug usually used for fungal infections. In addition to intravenous treatment, amphotericin B can be instilled directly into the brain (intrathecally). Unfortunately, amphotericin alone often fails, which has led clinicians to use additional drugs. It is strongly recommended that an infectious-diseases expert be consulted to guide therapy. The Centers for Disease Control and Prevention has a supply of a newer agent called miltefosine, which has shown promise in a limited number of recent cases. Miltefosine can be acquired by calling the CDC Emergency Operations Center at 770-488-7100.

    Other drugs such as rifampin (Rifadin), voriconazole (Vfend), or azithromycin (Zithromax, Zmax) have activity against Naegleria fowleri and may sometimes be used in combination with amphotericin B. However, there are no scientific studies available to determine the clinical efficacy of these medications and no official recommendation for their use.

    What is Naegleria fowleri?

    Naegleria fowleri is an amoeba that lives in freshwater and soil. The organism goes through three stages in its life cycle: cysts, flagellates, and trophozoites. Cysts are highly stable in the environment and can withstand near-freezing temperatures. The flagellate form is an intermediate stage that does not consume nutrients or reproduce. The trophozoite form causes human disease. Naegleria are "thermophilic," meaning that they prefer warmer water. Thus, Naegleria infection is found both in tropical and temperate climates. The organism is commonly identified in freshwater, including rivers, lakes, and ponds, or in soil near these sources. Where the water temperature is cool, Naegleria may be found in the sediment at the bottom of lakes or in localized areas where warmer water is discharged into lakes. Naegleria fowleri does not exist in saltwater and is not found in the ocean.

    Although there are many species of Naegleria, only Naegleria fowleri causes human infection. There are other free-living amoebas that cause human disease, including Acanthamoeba.

    What causes a Naegleria fowleri infection?

    N. fowleri infection is a water-borne disease. Exposure occurs when people come into contact with warm freshwater usually through swimming, diving, water skiing, or other recreational activity. Although contact with infected water is common in the United States, symptomatic disease caused by N. fowleri is rare.

    The danger of serious infection comes when water containing Naegleria fowleri is forced into the nose. The amoeba then migrates through the olfactory nerves and enters the brain. The initial exposure can occur when diving or inadvertently aspirating water during swimming. Rarely, underchlorinated swimming pools have been implicated in transmission. Because Naegleria fowleri can be present in untreated well water, there is a small but real chance of transmission to young children during bathing. Naegleria fowleri has also caused disease in adults who inject water into the nose as part of ritual ablutions related to religious practices or as an irrigating solution for sinus passages.

    What are risk factors for Naegleria fowleri infection?

    The source of nearly all of the 128 Naegleria fowleri infections reported since 1962 in the U.S. has been exposure to warm freshwater. These include freshwater lakes and rivers, particularly in Texas and Florida. More than one-quarter of all cases are reported from Florida and most cases have occurred in the South, although recent cases have been reported from Minnesota, from Lake Havasu City in Arizona, from Los Angeles in California, and other sites. Other freshwater sources have included hot springs, poorly chlorinated pools, untreated well water, water heaters, neti pots, and warm water discharge from power plants. Of the 31 cases reported from 2003 to 2012, 28 people acquired the disease from recreational exposure to freshwater and three people acquired it from irrigating their nose with contaminated tap water. There is a decided summertime predominance of cases, and even lakes in the southern States have higher levels of this microbe commonly during the warmer months.

    More than 75% of cases since 1962 were in children or adolescents, and 75% or more were in males. It is known that exposure of the olfactory nerve to contaminated water is the portal of entry to the brain. This exposure often results from water being forcefully introduced into the nose during trauma such as dunking, diving, or crashing while water skiing.

    Hundreds of millions of people go to swimming venues where N. fowleri is found, but fortunately very few become infected. We are unable to calculate an accurate estimate of the true risk of invasive Naegleria fowleri infection.

    What are symptoms and signs of a Naegleria fowleri infection?

    After entering the nose, the amoeba travels into the brain along the olfactory nerve and through membranes to enter the brain. Once in the brain, it causes primary amoebic meningoencephalitis (meaning inflammation of the brain and the lining around the brain), sometimes abbreviated as PAM.

    After exposure to the offending water source, there is generally a two-stage illness. A person infected with Naegleria fowleri will usually develop stage 1 symptoms within two to seven days of exposure.

    Stage 1 signs and symptoms include:

    • severe frontal headache,
    • fever,
    • nausea,
    • vomiting.

    Stage 2 usually begins one to 12 days after stage 1 and may include:

    • stiff neck,
    • seizures,
    • altered mental status,
    • hallucinations,
    • coma.

    The infection progresses so quickly that many people are not diagnosed until after death.

    How is a Naegleria fowleri infection diagnosed?

    Naegleria fowleri should be suspected in people, especially children, with exposure to freshwater who have symptoms of meningitis or meningoencephalitis listed above. The characteristics of the presentation may be nonspecific at first, leading clinicians to suspect more common diseases such as bacterial or viral meningitis. Routine tests may show a high blood white cell count and images of the brain may show inflammation, but neither of these are specific to PAM. A spinal tap will be done and the spinal fluid often shows elevated levels or white cells and red cells. Routine staining (Gram staining) does not detect the amoeba. Thus, it is important to do a wet mount to look for the motile amoeba under the microscope.

    Definitive tests for N. fowleri infection are done in only a few labs in the country. They use one of the following three methods:

    1. N. fowleri nucleic acid tests in CSF or biopsy tissue using PCR
    2. N. fowleri antigen tests in CSF or biopsy tissue using immunohistochemistry (IHC)
    3. It is also possible to culture N. fowleri, but this must be done in the presence of bacteria and at higher temperatures, which is not routinely done in most laboratories.

    What is the treatment for a Naegleria fowleri infection?

    Because Naegleria meningoencephalitis is rare, there are no studies comparing one treatment regimen to another.

    The treatment of choice is amphotericin B, which is an intravenous drug usually used for fungal infections. In addition to intravenous treatment, amphotericin B can be instilled directly into the brain (intrathecally). Unfortunately, amphotericin alone often fails, which has led clinicians to use additional drugs. It is strongly recommended that an infectious-diseases expert be consulted to guide therapy. The Centers for Disease Control and Prevention has a supply of a newer agent called miltefosine, which has shown promise in a limited number of recent cases. Miltefosine can be acquired by calling the CDC Emergency Operations Center at 770-488-7100.

    Other drugs such as rifampin (Rifadin), voriconazole (Vfend), or azithromycin (Zithromax, Zmax) have activity against Naegleria fowleri and may sometimes be used in combination with amphotericin B. However, there are no scientific studies available to determine the clinical efficacy of these medications and no official recommendation for their use.

    Source: http://www.rxlist.com

    The source of nearly all of the 128 Naegleria fowleri infections reported since 1962 in the U.S. has been exposure to warm freshwater. These include freshwater lakes and rivers, particularly in Texas and Florida. More than one-quarter of all cases are reported from Florida and most cases have occurred in the South, although recent cases have been reported from Minnesota, from Lake Havasu City in Arizona, from Los Angeles in California, and other sites. Other freshwater sources have included hot springs, poorly chlorinated pools, untreated well water, water heaters, neti pots, and warm water discharge from power plants. Of the 31 cases reported from 2003 to 2012, 28 people acquired the disease from recreational exposure to freshwater and three people acquired it from irrigating their nose with contaminated tap water. There is a decided summertime predominance of cases, and even lakes in the southern States have higher levels of this microbe commonly during the warmer months.

    More than 75% of cases since 1962 were in children or adolescents, and 75% or more were in males. It is known that exposure of the olfactory nerve to contaminated water is the portal of entry to the brain. This exposure often results from water being forcefully introduced into the nose during trauma such as dunking, diving, or crashing while water skiing.

    Hundreds of millions of people go to swimming venues where N. fowleri is found, but fortunately very few become infected. We are unable to calculate an accurate estimate of the true risk of invasive Naegleria fowleri infection.

    Source: http://www.rxlist.com

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