Naegleria fowleri

Naegleria fowleri is a highly pathogenic extra-intestinal amoeba with a high fatality rate

Disease / Pathology

Naegleria fowleri is the cause of primary amoebic meningoencephalitis (PAM). Organism attacks the brain and linings of the brain to casue massive inflammation and destruction.. It is introduced via nasal introduction after activities in which contaminated water is pushed up the nose as in jumping – diving – or falling into the water. Normally this amoeba is found most commonly in the warmer months or in warm water (25-40 degrees centigrade) that is stagnant. Poorly chlorinated pools and spas can be a source.

The infection is aggressive in nature and is usually fatal. Symptoms include high fever-severe persistent headache-neck stiffness-sleepiness-sore throat-nausea and vomiting-seizures and other neurological symptoms. Though symptoms mimic other CNS diseases … laboratory tests in conjunction with a good clinical history can lead to an accurate diagnosis. Small children and young adult are more prone though the amoeba can attack any age group. The age difference is perhaps related to the increased risk behavior.

Neti pots used for nasal cleansing – irrigation – or lavage can predispose persons to infection with this amoeba.

Even with treatment persons succumb to the disease. Once the symptoms appear the patients die within 10 days.

Location in the Host

Naegleria fowleri is found in the brain of the host

Geographic Distribution

Naegleria fowleri is found worldwide in warm standing pools of water. The organism cannot survive in clean water or water that is chlorinated or cool. 


No vector. Amoeba is contracted by the introduction of the cyst/troph into nasal passages.

Life Cycle

Image courtesy of CDC

Morphology & Diagnosis

Naegleria fowleri is detected by seeing motile amoeboid trophozoites in the CSF. This is the earliest type of definitive diagnosis. Brain biopsies post mortem will confirm the presence of characteristic cyst and trophozoite forms after staining.

Trophozoites are 8-15um with lobate pseudopodia in the amebic form. The cysts, which are not present in tissue, are small smoothly rounded with a diameter of 7-15um and a thick double wall. The flagellated form of the trophozoite is not normally present in the human host but in the water environment. However the flagellated form can sometimes be seen in cerebrospinal fluid.


Naegleria fowleri in brain tissue – image courtesy of CDC
Fluorescent stained Naegleria fowleri – image courtesy of CDC
Naegleria fowleri in brain tissue – image courtesy of CDC