Naegleria fowleri – Deadly Amoeba

Agent of Primary Amebic Meningoencephalitis, a Fatal Meningitis

Sep 11, 2007 Rosemary Drisdelle

Naegleria fowleri lurks in warm waters and in rare isolated instances infects humans and animals. Few survive primary amebic meningoencephalitis (PAM).

Naegleria fowleri is a protozoan in the taxonomic Family Vahlkamphidae, a microscopic organism that lives in soil, sewage, and warm water and very rarely causes parasitic disease in humans and animals. When it does, the illness is devastating. Parasitic disease caused by Naegleria fowleri is called primary amebic meningoencephalitis (PAM).

Life cycle of Naegleria fowleri

Naegleria fowleri, often referred to as simply “naegleria,” 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 and is probably the stage that infects people who are exposed through water. Within the body, the flagellate converts to an amoeba, a slow moving single-celled organism that proliferates by dividing 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.

What is primary amebic meningoencephalitis?

Primary amebic meningoencephalitis is a form of infectious meningitis—the organism grows in the brain and the meninges (the tissue membranes that surround the brain) -- that is almost always rapidly fatal. Most people who develop this parasitic disease have a fairly recent history of exposure to warm and possibly stagnant water: small lakes where the water gets very warm in summer, thermal pools, water heated by effluent from industrial processes, still warm reservoirs, etc. Naegleria fowleri usually enters the body when water is drawn in through the nose:

• Flagellates of N. fowleri change to the amebic form in the nasal passages and invade tissue by traveling up the olfactory nerve, the nerve responsible for communicating smells to the brain. The early symptoms of PAM often include nasal congestion and problems with the sense of smell. Other symptoms include headache, vomiting, and lack of energy.
• Amoebae of N. fowleri invade the brain and begin to multiply. The patient develops a fever and may have a sore throat and stiff neck.
• The disease progresses swiftly as the parasite continues to multiply unchecked. The patient suffers mental confusion and, later, coma. Most people with this parasitic disease die within about six days of becoming ill. In a few cases, where physicians were able to diagnose the problem very early, antiparasitic drug therapy has been effective.

Avoid Naegleria fowleri and primary amebic meningoencephalitis

Parasitic disease caused by naegleria is very rare—only a few hundred cases have ever been reported—however a few common sense precautions will protect people from acquiring this and other water borne infections:

• Avoid swimming in very warm water, especially if it is shallow and/or stagnant (not moving). The majority of PAM cases have resulted from exposure to water that is 26C (80F) or warmer.
• Avoid taking in water through the nose while swimming, diving, water skiing, or jumping into water. A nose clip can be used to prevent water being forced up the nose.
• Stay out of the water if “No Swimming” signs are posted.
• Do not swim in swimming pools that are very warm or that are not properly maintained, even if the water is chlorinated. Naegleria fowleri is resistant to chlorine.

Read about other waterborne parasites:

Acanthamoeba - Eye Parasite

Toxoplasma gondii

Cryptosporidium parvum - Parasite

Other interesting articles in Microbiology

Sources:

Clinical Parasitology 9th ed. Beaver, Paul Chester, Rodney Clifton Jung, and Eddie Wayne Cupp. Philadelphia: Lea and Febiger, 1984.

Diagnostic Medical Parasitology 3rd ed. Garcia, Lynn S. and David A. Bruckner. Washington: ASM Press, 1997.

Foundations of Parasitology 6th Ed. Roberts, Larry S. and John Janovy Jr. Boston: McGraw Hill, 2000.

The copyright of the article Naegleria fowleri – Deadly Amoeba in Microbiology is owned by Rosemary Drisdelle. Permission to republish Naegleria fowleri – Deadly Amoeba in print or online must be granted by the author in writing.