Naegleria fowleri
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 Different stages of Naegleria fowleri
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| Naegleria fowleri Carter (1970) |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Naegleria fowleri, commonly referred to as the "brain-eating amoeba" or "brain-eating ameba", is a free-living microscopic ameba, (single-celled living organism). It can cause a rare and devastating infection of the brain called primary amebic meningoencephalitis (PAM).[1] The ameba is commonly found in warm freshwater (e.g. lakes, rivers, and hot springs) and soil. Naegleria fowleri usually infects people when contaminated water enters the body through the nose. Once the ameba enters the nose, it travels to the brain where it causes PAM, which is usually fatal. Infection 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 heated and contaminated tapwater) enters the nose. This infection will nearly always result in the death of the victim. [2]
Epidemiology and Demographics
The first PAM infections were reported in 1965 in Australia. The ameba identified caused a fatal infection in 1961 and turned out to be a new species that has since been named Naegleria fowleri after one of the original authors of the report, M. Fowler. The first infections in the U.S., which occurred in 1962 in Florida, were reported soon after. Subsequent investigations in Virginia using archived autopsy tissue samples identified PAM infections that had occurred in Virginia as early as 1937.
PAM infections have been reported from around the world. Infections have primarily occurred in southern-tier states in the U.S., but infections were documented in Minnesota in 2010 and 2012. Over half of all reported infections have occurred in Florida and Texas. In the United States and the rest of the world, PAM is primarily spread via swimming in warm freshwater lakes and rivers (about 3 out of 4 U.S. infections from 1962-2012). Other recreational water types like hot springs and canals have also been linked to PAM infections.
Four infections in the U.S. have been associated with using water from drinking water systems to swim, immerse the head in a bathtub, or mix solutions for nasal irrigation using a neti pot. PAM infections also occurred in the 1970s and 1980s in Australia that were linked to showering, swimming, or having other nasal exposure to contaminated drinking water. The infections were linked to piping drinking water overland, sometimes for hundreds of kilometers, that resulted in the water being heated and having low disinfectant levels that resulted in the water and pipes becoming colonized by Naegleria fowleri. Several water systems in the states of Western Australia and South Australia continue to have to monitor regularly for Naegleria fowleri colonization in drinking water distribution systems 20. Infections due to contaminated water being used for religious practices have also been reported.
Pathophysiology
Naegleria fowleri is a heat-loving (thermophilic), free-living ameba (single-celled microbe), commonly found around the world in warm fresh water (like lakes, rivers, and hot springs) and soil. Naegleria fowleri is the only species of Naegleria known to infect people. Most of the time, Naegleria fowleri lives in freshwater habitats by feeding on bacteria. However, in rare instances, the ameba can infect humans by entering the nose during water-related activities. Once in the nose, the ameba travels to the brain and causes a severe brain infection called primary meningoencephalitis (PAM), which is usually fatal.
Life Cycle
Naegleria fowleri has 3 stages in its life cycle: ameboid trophozoites, flagellates, and cysts. The only infective stage of the ameba is the ameboid trophozoite. Trophozoites are 10-35 µm long with a granular appearance and a single nucleus. The trophozoites replicate by binary division during which the nuclear membrane remains intact (a process called promitosis). Trophozoites infect humans or animals by penetrating the nasal tissue and migrating to the brain via the olfactory nerves causing primary amebic meningoencephalitis (PAM).
Trophozoites can turn into a temporary, non-feeding, flagellated stage (10-16 µm in length) when stimulated by adverse environmental changes such as a reduced food source. They revert back to the trophozoite stage when favorable conditions return. Naegleria fowleri trophozoites are found in cerebrospinal fluid (CSF) and tissue, while flagellated forms are occasionally found in CSF. Cysts are not seen in brain tissue. If the environment is not conducive to continued feeding and growth (like cold temperatures, food becomes scarce) the ameba or flagellate will form a cyst. The cyst form is spherical and about 7-15 µm in diameter. It has a smooth, single-layered wall with a single nucleus. Cysts are environmentally resistant in order to increase the chances of survival until better environmental conditions occur.
Environmental Resistance
Naegleria fowleri is normally found in the natural environment and is well adapted to surviving in various habitats, particularly warm-water environments. Although the trophozoite stage is relatively sensitive to environmental changes, the cysts are more environmentally hardy. There are no means yet known that would control natural Naegleria fowleri levels in lakes and rivers.
Drying: Drying appears to make trophozoites nonviable instantaneously and cysts nonviable in <5 min.
Temperature: Naegleria fowleri is a heat-loving (thermophilic) ameba able to grow and survive at higher temperatures, such as those found in hot springs and in the human body, even under fever temperatures. Naegleria fowleri grows best at higher temperatures up to 115°F (46°C). Although the amebae may not be able to grow well, Naegleria fowleri can still survive at higher temperatures for short periods of time. The trophozoites and cysts can survive from minutes to hours at 122-149°F (50-65°C) with the cysts being more resistant at these temperatures. Although trophozoites are killed rapidly by refrigeration, cysts can survive for weeks to months at cold temperatures above freezing, although they appear to be sensitive to freezing 9, 11. As a result, colder temperatures are likely to cause Naegleria fowleri to encyst in lake and river sediment where the cyst offers more protection from freezing water temperatures.
Disinfection: Naegleria fowleri trophozoites and the more resistant cysts are sensitive to chlorination and monochloramine used for disinfection of drinking water and swimming pools if adequate levels are maintained and monitored. The chlorine sensitivity is moderate and in the same range as the cysts from Giardia intestinalis, another waterborne pathogen.
Salinity: Naegleria fowleri does not survive in sea water and has not been detected in sea water.
Risk Factors
High Temperature
Naegleria fowleri is a heat-loving (thermophilic) ameba found around the world. Naegleria fowleri grows best at higher temperatures up to 115°F (46°C; see Pathogen and Environment page) and can survive for short periods at higher temperatures.
Warm Fresh Water
Naegleria fowleri is naturally found in warm freshwater environments such as lakes and rivers, naturally hot (geothermal) water such as hot springs, warm water discharge from industrial or power plants, geothermal well water, poorly maintained or minimally chlorinated swimming pools, water heaters, and soil, where it lives by feeding on bacteria and other microbes in the environment. Sampling of lakes in the southern tier of the U.S. indicates that Naegleria fowleri is commonly present in many southern tier lakes in the U.S. during the summer. Naegleria is not found in salt water, like the ocean.
Infection
In humans, N. fowleri can invade the central nervous system via the nose, more specifically the olfactory mucosa and nasal tissues. The penetration initially results in significant necrosis of and hemorrhaging in the olfactory bulbs. From there, amoebae climb along nerve fibers through the floor of the cranium via the cribriform plate and into the brain. It then becomes pathogenic, causing primary amoebic meningoencephalitis (PAM or PAME). PAM is a syndrome affecting the central nervous system, characterized by changes in olfactory perception (taste and smell), followed by vomiting, nausea, fever, headache, and the rapid onset of coma and death in two weeks.
PAM usually occurs in healthy children or young adults with no prior history of immune compromise who have recently been exposed to bodies of fresh water.
Amphotericin B is currently the most effective known pharmacologic treatment for N. fowleri, but the prognosis remains bleak for those that contract PAM, as only eight patients have survived (3% survival rate) in a clinical setting. Amphotericin B devastates N. fowleri organisms in laboratory settings; it, in combination with systemic rifampicin, is the preferred choice in N. fowleri treatment.
A more aggressive antibody serum-based treatment is being pursued, and may eventually prove more effective than modern broad-spectrum antibiotic targeting.
Timely diagnosis remains a very significant impediment to the successful treatment of infection, as most cases have only been appreciated post-mortem. It killed 23 people in the US from 1995 to 2004, and has killed six in the year of 2007 (3 in Florida, 2 in Texas, and 1 in Arizona).
Detection
N. fowleri can be grown in several kinds of liquid axenic media or on non-nutrient agar plates coated with bacteria. Detection in water is performed by centrifuging a water sample with Escherichia coli added, and then applying the pellet to a non-nutrient agar plate. After several days the plate is microscopically inspected and Naegleria cysts are identified by their morphology. Final confirmation of the species' identity can be performed by various molecular or biochemical methods.[3] Confirmation of Naegleria presence can be done by so called flagellation test, when amoeba is exposed to hypotonic environment (distilled water). Naegleria in contrast to other amoebae differentiates within two hours into flagellar state. Pathogenicity can be further confirmed by exposition to high temperature (42°C), where is Naegleria fowleri as pathogenic species of Naegleria able to grow in contrast to Naegleria gruberi etc.
Incidents and outbreaks
Czech Republic
- Between years 1962–1965, 16 young persons died of acute meningoencephalitides in Ústí nad Labem as a consequence of bathing in an indoor swimming pool.[4]
United States
According to the Centers for Disease Control and Prevention, the amoeba killed 23 people between 1995 and 2004.
- In August 2005, two Oklahoma boys, ages 7 and 9 were killed by N. fowleri after swimming in hot stagnant water of the lakes in the Tulsa area.[5]
- In 2007, six cases were reported in the U.S., all fatal:[6]
- In July, the amoeba caused the deaths of three boys in lakes around Orlando, Florida. Possible causes of the infections include higher temperature and droughts in that area of Florida.[7]
- In late summer, the amoeba caused the death of a 12-year-old boy and a 22-year-old young man in Lake LBJ in Texas.[8][2]
- In September, a 14-year-old boy was killed by the amoeba after likely having caught it while swimming in Lake Havasu in Arizona. The doctors suspected meningitis before the boy died, but did not know the etiology until the CDC confirmed it as N. fowleri.[9][10]
Pop culture references
- Naegleria fowleri was featured on the TV show House, in a two-part season 2 episode ("Euphoria" parts 1 and 2). The writers took dramatic license with one of the disease's symptoms. Both characters developed Anton's blindness, a condition affecting the occipital lobes where the patient thinks he can see but really cannot. This is not consistent with N. fowleri, whose initial symptoms are "alteration in taste (ageusia) or smell (parosmia)".[11]
- A "brain-sucking amoeba" that infects swimmers was mentioned in the season 1 episode of The X-files, "Darkness Falls"
References
- ↑ "The Centers for Disease Control and Prevention, Division of Parasitic Diseases - Naegleria Infection Fact Sheet". Retrieved 2007-10-09.
- ↑ "6 Die From Brain-Eating Amoeba in Lakes". Retrieved 2007-10-03.
- ↑ Pougnard; et al., "Rapid Detection and Enumeration of Naegleria fowleri in Surface Waters by Solid-Phase Cytometry", Applied and Environmental Microbiology, 68 (6), pp. 3102–3107, retrieved 2007-07-18
- ↑ Červa, L. (April 5, 1968). "Ameobic meningoencephalitis: sixteen fatalities". Science. 160: 92. Unknown parameter
|coauthors=ignored (help); Check date values in:|date=(help) - ↑ "Parasitic Infection Kills Two Tulsa Swimmers". Retrieved 2005-08-06.
- ↑ Six Die From Brain-Eating Amoeba in Lakes, an Associated Press article via The Washington Post
- ↑ "Deadly amoeba lurks in Florida lakes". Retrieved 2007-07-19.
- ↑ "Deadly lake disease causing concern in Texas". Retrieved 2007-09-10.
- ↑ "Brain-Eating Amoeba Kills Arizona Boy". Retrieved 2007-09-27.
- ↑ "Arizona Teen Becomes Sixth Victim This Year of Brain-Eating Amoeba". Retrieved 2007-09-27.
- ↑ Barnett Gibbs, MD. "Naegleria Infection". emedicine. Retrieved 2007-07-19. Unknown parameter
|coauthors=ignored (help)
External links
- Naegleria Infection fact sheet from the website of the Centers for Disease Control and Prevention
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