Parasite profile: The "brain-eating" Naegleria fowleri

Naegleria fowleri is a parasitic amoebo-flagellate that infects humans, causing severe illness and in many cases, death. This single-celled protist can be found in warm freshwater bodies, soil, and various contaminated water sources.

 Photo credit: www.soakersforum.com

Life Cycle


Naegleria fowleri can exist in three different forms during its life cycle: a cyst, a trophozoite, and a flagellate. The cyst is environmentally resistant and can protect the parasite during periods of poor environmental conditions. Once favorable conditions return, the parasite excysts as a trophozoite where it feeds and reproduces via binary fission. The trophozoite can then go on to the encysted or free-swimming flagellated form.

Life cycle stages for  N. fowleri from left to right: Cyst, trophozoite, flagellate. Photo credit: Wikipedia

How do people become infected?

Humans can become infected with N. fowleri when swimming in lakes, ponds, or untreated swimming pools, playing water sports, or even when irrigating sinuses with contaminated water. In addition, it is purported that inhaling viable cysts in dust can also lead to infection. Once the parasite contacts the nasal epithelium, it travels up the nasal mucosa and to the brain through the olfactory nerves.

Photo credit: Centers for Disease Control and Prevention

Symptoms, diagnostics, and treatment

    

Once the parasite enters the brain, it causes primary amebic meningoencephalitis (PAM), which is fatal in almost all cases. 

The onset of PAM is characterized by the following symptoms:

-fever

-headache

-changes in sense of smell or taste (due to destruction of the olfactory bulbs)

-stiff neck

-sensitivity to light

-changes in mental status

-seizures

-coma

-death  

Cerebrospinal fluid or tissue samples may be collected and analyzed for the presence of trophozoites. Treatment usually consists of administering high doses of amphotericin B and miconazole, although it is suggested that the rapid progression of infection makes successful treatment very difficult. As such, patients exhibit a high mortality rate.

Find out more about Naegleria fowleri:

Centers for Disease Control:
http://www.cdc.gov/parasites/naegleria/

National Society for Biotechnology Information:
http://www.ncbi.nlm.nih.gov/books/NBK7960/

Medscape:
http://emedicine.medscape.com/article/223910-overview