Naegleria Fowler

Naegleria fowleri is a thermophilic, free-living ameba that resides in warm freshwater habitats and feeds on bacteria. Naegleria fowleri is the only species of Naegleria known to infect people.

Naegleria fowleri is found in fresh water, soil, thermal discharges of power plants, geothermal wells, and poorly chlorinated recreational and tap water. Most infections have been linked to swimming in southern states, but infections have also occurred after using contaminated tap water for nose or sinus irrigation. 

Naegleria fowleri causes primary amebic encephalitis by penetrating the nasal mucosa and migrating to the brain via the olfactory nerves. Symptoms start 1 to 12 days (median 5 days) after exposure to contaminated water. Symptoms include severe frontal headache, fever, nausea, vomiting, stiff neck, seizures, altered mental status, and coma. The disease is usually fatal with people dying a median of 5 days (range 1 to 18 days) after symptom onset. 

The United States averages from 0 to 5 cases each year and has recorded 31 cases between 2012 and 2021. Of those, 2 patients contracted the ameba after rinsing their sinuses using contaminated tap water. 

Primary amebic encephalitis can be diagnosed in the laboratory by detecting Naegleria fowleri organisms or nucleic acid, or in a patient’s cerebrospinal fluid (CSF) or brain tissue.A wet mount of freshly centrifuged CSF sediment might demonstrate actively moving trophozoites. Naegleria can also be identified in CSF smears or cultures using hematoxylin and eosin (H&E), periodic acid-Schiff (PAS), trichrome, Giemsa, or Wright-Giemsa stains.

CDC has developed a qualitative real-time PCR that simultaneously tests for three free-living amebae including Naegleria fowleri, Acanthamoeba spp., and Balamuthia mandrillaris.

Serologic testing for Naegleria fowleri antibodies patient is not helpful because most patients die before an immune response is mounted.

Specimen requirements are fresh cerebrospinal fluid or fresh brain tissue. Formalin fixed paraffin embedded brain tissue can be submitted for histological examination.

References

Centers for Disease Control and Prevention, Naegleria fowleri Infections, https://www.cdc.gov/naegleria/about/?CDC_AAref_Val=https://www.cdc.gov/parasites/naegleria/index.html

Visvesvara GS, Moura H, Schuster FL. Pathogenic and opportunistic free-living amoebae: Acanthamoeba spp., Balamuthia mandrillaris, Naegleria fowleri, and Sappinia diploidea. FEMS Immunol Med Microbiol 2007;50:1–26.

Shakoor S, Beg MA, Mahmood SF, et al. Primary amebic meningoencephalitis caused by Naegleria fowleri, Karachi, Pakistan. Emerg Infect Dis 2011;17:258–61.

Yoder JS, Straif-Bourgeois S, Roy SL, et al. Primary amebic meningoencephalitis deaths associated with sinus irrigation using contaminated tap water. Clin Infect Dis 2012;55:e79–85.

CDC. Notes from the field: primary amebic meningoencephalitis associated with ritual nasal rinsing—St. Thomas, U.S. Virgin Islands, 2012. MMWR Morb Mortal Wkly Rep 2013;62:903.

Smith OA, Tillman W, Lewis JB, et al. Notes from the Field: Primary Amebic Meningoencephalitis Associated with Nasal Irrigation Using Water from a Recreational Vehicle — Texas, 2024. MMWR Morb Mortal Wkly Rep 2025;74:334–335.