Naegleria fowleri is a free living, flagellated freshwater ameba usually found in rivers, lakes, geothermal springs and spas, canals, warm water discharges from power plants and inadequately treated swimming pools and domestic water supplies. The density of the ameba increases during the hot summer months. The ameba feeds on bacteria and organic debris. It can exist in three forms, namely, cyst form (stable in the environment), trophozoite form (motile amoeboid form) and flagellate form. (1)

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Naegleria fowleri is also known as brain eating ameba as this ameba has a tendency to enter brain via nostrils. Mostly, the ameba enters nostrils through contaminated water when this water is inhaled deeply during swimming, jumping or diving in ameba containing water. N. fowleri invade brain via olfactory nerves and cribriform plate and causes extensive brain tissue damage within a few days leading to severe inflammation and hemorrhaging. This CNS involvement due to Naegleria fowleri infection is termed as primary amebic meningoencephalitis. (1)

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Naegleria fowleri is coined after an Australian pathologist, Malcolm Fowler who was the first to isolate it from a patient with primary amebic meningoencephalitis. Bull was the one to term the disease by Naegleria fowleri “primary amebic meningoencephalitis” so that it could be differentiated from secondary meningoencephalitis, which is caused by Entamoeba histolytica, an intestinal ameba. Although, 30 different species of Naegleria have been recognized and other Naegleria species (Naegleria italica, Naegleria australiensis, Naegleria philippinensis) cause primary amebic meningoencephalitis in murine models, only Naegleria fowleri has been isolated from human cases, so far. (2)

Naegleria fowleri infection is a rare disease with total of 440 and 143 reported cases all around the world and United States by 2008 and 2016, respectively. The risk of Naegleria fowleri infection is estimated at 1 in every 2.6 million exposures. Though, primary amebic meningoencephalitis is a rare disease, it is associated with high mortality, exceeding over 95%. Very few survivors have been reported in US (4 out of 143 until 2016) and worldwide (total of 8 until 2005). The rare survivors were due to early identification and diagnosis facilitating prompt aggressive intervention. Most of the survivors are found with physical or mental disability. (2)

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Symptoms Of Primary Amebic Meningoencephalitis

Although, most of the cases of primary amebic meningoencephalitis have a previous history of swimming, there have few cases where the disease occurred due to exposure to tap water in the form of ablution and use of neti pots. Infection should be suspected in children and young adults with a past history of swimming in lakes, ponds and swimming pools. The symptoms usually appear 2-6 days after exposure to contaminated water, especially during summer months. (2)

The signs and symptoms of primary amebic meningoencephalitis are similar to those of bacterial meningitis and include, fever, nausea or vomiting, change in sense of smell and taste, sudden headache (in frontal and bitemporal region), neck stiffness, sensitivity to light, altered mental status, hallucinations, seizures, cranial nerve palsies, coma and death. Positive Kernig and Brudzinski signs are also noted. Primary amebic meningoencephalitis is usually fatal. Death usually occurs due to cardiorespiratory arrest and pulmonary edema. The progression of disease is rapid and death usually happens within 1-2 weeks of symptomatology. In recuperated patients, persistence of seizures may be noted. (2)

Since, the disease is acute, fulminant and fatal; the survival of a patient with primary amebic meningoencephalitis is largely dependent on early diagnosis and aggressive treatment. The treatment is usually done with anti-fungal medications, such as amphotericin B, miconazole, fluconazole and antimicrobial rifampin, in addition to ventriculoperitoneal shunt in cases of obstructive hydrocephalus. Amphoterin B is the drug of choice since Naegleria is known to be highly sensitive to this antifungal drug. Various new drugs have been studied including chlorpromazine, miltefosine and corifungin that have shown efficacy against Naegleria species, both in vivo and in vitro. To avoid this fatal infection, it is imperative to stay away from contaminated water and avoiding entry of water into nostrils. (2)

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Sheetal DeCaria MD

Written, Edited or Reviewed By:

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Last Modified On: June 11, 2019

This article does not provide medical advice. See disclaimer

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