Naegleria infection

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Naegleria is a free-living amoeba commonly found in the environment in water and soil. Infection of humans is rare but serious. To prevent infection with Naegleria, precautions should be taken to ensure that water does not enter the nose when participating in recreational water sports.

Only one species (type) of Naegleria infects people: Naegleria fowleri.

Infection with Naegleria is very rare. However, when it does occur, infection is most common during the dry, summer months, when the air temperature is hot, the water is warm, and water levels are low. The number of infections increase during years characterized by heat waves.

After the start of symptoms, the disease progresses rapidly and usually causes death within about 5 days (range 1 to 12 days).

Naegleria fowleri causes the disease primary amebic meningoencephalitis (PAM), a brain infection that leads to the destruction of brain tissue. 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.

In Naegleria infections, the diagnosis can be made by microscopic examination of cerebrospinal fluid (CSF). A wet mount may detect motile trophozoites, and a Giemsa-stained smear will show trophozoites with typical morphology. Confocal microscopy or cultivation of the causal organism, and its identification by direct immunofluorescent antibody, may also prove useful. An increasing number of PCR-based techniques (conventional and real-time PCR) have been described for detection and identification of free-living amoebic infections in the clinical samples. Such techniques may be available in selected reference diagnostic laboratories.

Several drugs are effective against Naegleria fowleri in the laboratory. However, their effectiveness is unclear since almost all infections have been fatal, even when people were treated. Amphotericin B has been successfully used in some cases to treat PAM caused by Naegleria fowleri.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Free-living amebae belonging to the genera Acanthamoeba, Balamuthia, and Naegleria are important causes of disease in humans and animals. Naegleria fowleri produces an acute, and usually lethal, central nervous system (CNS) disease called primary amebic meingoencephalitis (PAM).

N. fowleri has three stages, cysts 1, trophozoites 2, and flagellated forms 3, in its life cycle. The trophozoites replicate by promitosis (nuclear membrane remains intact) 4. Naegleria fowleri is found in fresh water, soil, thermal discharges of power plants, heated swimming pools, hydrotherapy and medicinal pools, aquariums, and sewage. Trophozoites can turn into temporary non-feeding flagellated forms which usually revert back to the trophozoite stage. Trophozoites infect humans or animals by entering the olfactory neuroepithelium 5 and reaching the brain. N. fowleri trophozoites are found in cerebrospinal fluid (CSF) and tissue, while flagellated forms are occasionally found in CSF.

Acanthamoeba spp. and Balamuthia mandrillaris are opportunistic free-living amebae capable of causing granulomatous amebic encephalitis (GAE) in individuals with compromised immune systems. Acanthamoeba spp. have been found in soil; fresh, brackish, and sea water; sewage; swimming pools; contact lens equipment; medicinal pools; dental treatment units; dialysis machines; heating, ventilating, and air conditioning systems; mammalian cell cultures; vegetables; human nostrils and throats; and human and animal brain, skin, and lung tissues. B. mandrillaris has only recently been isolated from the environment and has also been isolated from autopsy specimens of infected humans and animals.

Unlike N. fowleri, Acanthamoeba and Balamuthia have only two stages, cysts 1 and trophozoites 2, in their life cycle. No flagellated stage exists as part of the life cycle. The trophozoites replicate by mitosis (nuclear membrane does not remain intact) 3. The trophozoites are the infective forms and are believed to gain entry into the body through the lower respiratory tract, ulcerated or broken skin and invade the central nervous system by hematogenous dissemination 4. Acanthamoeba spp. can also cause severe keratitis in otherwise healthy individuals, particularly contact lens users 4. Acanthamoeba spp. and Balamuthia mandrillaris cysts and trophozoites are found in tissue. Naegleria infection cannot be spread from person-to-person contact.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Only one species (type) of Naegleria infects people: Naegleria fowleri.’

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Naegleria fowleri is found worldwide. Most commonly, the amoeba is found in:

• Warm bodies of freshwater, such as lakes, rivers
• Geothermal water such as hot springs
• Warm water discharge from industrial plants
• Minimally chlorinated swimming pools
• Soil

Although Naegleria is commonly found in the environment, infection occurs rarely. Only 23 infections were documented in the U.S. between 1995 and 2004.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Infection with Naegleria is very rare. However, when it does occur, infection is most common during the dry, summer months, when the air temperature is hot, the water is warm, and water levels are low. The number of infections increase during years characterized by heat waves.

Naegleria fowleri is found around the world. In the United States, the majority of infections have been caused by Naegleria fowleri from warm freshwater located in southern-tier states. The ameba can be found in:

• Factors that can increase your risk of meningitis include:
• Bodies of warm freshwater, such as lakes and rivers
• Geothermal (naturally hot) water, such as hot springs
• Warm water discharge from industrial plants
• Geothermal (naturally hot) drinking water sources
• Soil
• Swimming pools that are poorly maintained, minimally-chlorinated, and/or un-chlorinated
• Water heaters with temperatures less than 47°C

Naegleria fowleri is not found in salt water, like the ocean.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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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