Naegleria fowleri
D'Larin Muehler

Naegleria fowleri is a free-living protist found mostly in warm water between 25 and 35 degrees Celsius. Naegleria can cause a very rare parasitic disease in animals and humans, called primary amebic meningoencephalitis (PAM) which affects the central nervous system and eventually the brain. It is commonly referred to as simply “naegleria.” It exists in nature in three forms: a flagellate, an amoeba, and a cyst. The flagellate stage, a small pear-shaped organism with two long whip-like flagellae at one end, is very mobile. This is the stage that would infect people through water. Within the body, the flagellate converts to an amoeba, a slow moving single-celled organism that divides repeatedly. Returned to water, and occasionally in human spinal fluid, the amoeba will once again assume the flagellate form. The cyst stage, a tough spherical stage found only in the environment, forms when conditions are unfavorable for naegleria.

Although N fowleri rarely causes disease, it can be difficult to diagnose and PAM is rapidly fatal in more than 95% of cases. It invades the central nervous system, climbing the olfactory nerve where it can cause swelling of the brain or linings of the brain. PAM is characterized by changes in olfactory perception, followed by vomiting, nausea, fever, headache, and the rapid onset of coma and death in two weeks. It can be detected in several ways. One of these is a flagellation test, in which 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): Naegleria fowleri is able to grow at this temperature.

It is found mostly in soil or warm, stagnant bodies of water, such as lakes, rivers, hot springs, and unchlorinated pools. Infection usually results from swimming in a lake or stream. The microbe enters through the nose and reaches the olfactory nerve from there. Naegleria fowleri trophozoites, cultured from cerebrospinal fluid  have characteristically large nuclei, with a large, dark staining karyosome. The amoebae are very active and extend and retract pseudopods. Most diagnoses are made during autopsy, but there have been patients who survived by being treated with amphotericin B.

Trichrome stain from a patient who died from primary amoebic meningoencephalitis in Virginia:

*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.


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