CDC Parasites

Sources of Infection & Risk Factors

Naegleria fowleri is a free-living ameba that causes primary amebic meningoencephalitis (PAM), a disease of the central nervous system 1, 2. PAM is a rare disease* that is almost always fatal. In the United States**, there have been 143 PAM infections from 1962 through 2016 with only four survivors. These infections have primarily occurred in 15 southern-tier states, with more than half of all infections occurring in Texas and Florida. PAM also disproportionately affects males and children. The reason for this distribution pattern is unclear but may reflect the types of water activities (such as diving or watersports) that might be more common among young boys 3.

Naegleria fowleri is a heat-loving (thermophilic) ameba found around the world 1, 2. Naegleria fowleri grows best at higher temperatures up to 115°F (46°C; see Pathogen and Environment page) and can survive for short periods at higher temperatures 3, 4. Naegleria fowleri is naturally found in warm freshwater environments such as lakes and rivers 5-9, naturally hot (geothermal) water such as hot springs 10, warm water discharge from industrial or power plants 11, 12, geothermal well water 13, 14, poorly maintained or minimally chlorinated swimming pools 15, water heaters 16, and soil 5, where it lives by feeding on bacteria and other microbes in the environment. Sampling of lakes in the southern tier of the U.S. indicates that Naegleria fowleri is commonly present in many southern tier lakes in the U.S. during the summer 5-9 but infections have also recently occurred in northern states 17. Naegleria is not found in salt water, like the ocean.

References
  1. Marciano-Cabral F, Cabral G. The immune response to Naegleria fowleri amebae and pathogenesis of infection. FEMS Immunol Med Microbiol.2007;51:243-59.
  2. Visvesvara GS. Free-living amebae as opportunistic agents of human disease. J Neuroparasitol. 2010;1.
  3. Griffin JL. Temperature tolerance of pathogenic and nonpathogenic free-living amoebas. Science. 1972;178(4063):869-70.
  4. Chang SL. Resistance of pathogenic Naegleria to some common physical and chemical agents.[PDF – 8 pages] Appl Environ Microbiol. 1978;35:368-75.
  5. Maclean RC, Richardson DJ, LePardo R, Marciano-Cabral F. The identification of Naegleria fowleri from water and soil samples by nested PCR. Parasitol Res. 2004;93(3):211–17.
  6. Wellings FM, Amuso PT, Chang SL, Lewis AL. Isolation and identification of pathogenic Naegleria from Florida lakes. Appl Environ Microbiol. 1977;34:661–7.
  7. John DT, Howard MJ. Seasonal distribution of pathogenic free-living amebae in Oklahoma waters. Parasitol Res. 1995;81(3):193–201.
  8. Duma RJ. Study of pathogenic free-living amebas in fresh-water lakes in Virginia. EPA Publication. 1980;EPA-PB-126369, Summary, 1981 is EPA-600/S1-80-037.
  9. Ettinger MR, Webb SR, Harris SA, McIninch SP, C Garman G, Brown BL. Distribution of free-living amoebae in James River, Virginia, USA. Parasitol Res. 2003;89(1):6-15.
  10. Sheehan KB, Fagg JA, Ferris MJ, Henson JM. PCR detection and analysis of the free-living amoeba Naegleria in hot springs in Yellowstone and Grand Teton National Parks. Appl Environ Microbiol. 2003;69:5914-8.
  11. Sykora JK, Keleti G, Martinez AJ. Occurrence and pathogenicity of Naegleria fowleri in artificially heated waters. Appl Envion Microbiol. 1983;45(3):974-9.
  12. Stevens AR, Tyndall RL, Coutant CC, Willaert E. Isolation of the etiological agent of primary amoebic meningoencephalitis from artificially heated waters. Appl Environ Microbiol. 1977;34(6):701-5.
  13. Marciano-Cabral F, MacLean R, Mensah A, LaPat-Polasko L. Identification of Naegleria fowleri in domestic water sources by nested PCR. Appl Environ Microbiol. 2003;69(10):5864-9.
  14. Blair B, Sarkar P, Bright KR, Marciano-Cabral F, Gerba CP. Naegleria fowleri in well water. Emerg Infect Dis. 2008;14(9):1499-501.
  15. Yoder JS, Eddy BA, Visvesvara GS, Capewell L, Beach MJ. The epidemiology of primary amoebic meningoencephalitis in the USA, 1962-2008. Epidemiol Infect. 2010;138(7):968-75.
  16. Yoder JS, Straif-Bourgeois S, Roy SL, Moore TA, Visvesvara GS, Ratard RC, Hill V, Wilson JD, Linscott AJ, Crager R, Kozak NA, Sriram R, Narayanan J, Mull B, Kahler AM, Schneeberger C, da Silva AJ, Beach MJ. Deaths from Naegleria fowleri associated with sinus irrigation with tap water: a review of the changing epidemiology of primary amebic meningoencephalitis. Clin Infect Dis. 2012;1-7.
  17. Kemble SK, Lynfield R, DeVries AS, Drehner DM, Pomputius WF 3rd, Beach MJ, Visvesvara GS, da Silva AJ, Hill VR, Yoder JS, Xiao L, Smith KE, Danila R. Fatal Naegleria fowleri infection acquired in Minnesota: possible expanded range of a deadly thermophilic organism. Clin Infect Dis. 2012;54:805-9.
References
  1. Marciano-Cabral F, Cabral G. The immune response to Naegleria fowleri amebae and pathogenesis of infection. FEMS Immunol Med Microbiol.2007;51:243-59.
  2. Visvesvara GS. Free-living amebae as opportunistic agents of human disease. J Neuroparasitol. 2010;1.
  3. Yoder JS, Eddy BA, Visvesvara GS, Capewell L, Beach MJ. The epidemiology of primary amoebic meningoencephalitis in the USA, 1962-2008. Epidemiol Infect. 2010;138:968-75.

*Rare Disease
There is no universal definition of a “rare disease” but the U.S. Rare Disease Act of 2002 defined a rare disease as affecting less than 200,000 people in the U.S. and this definition has been adopted by the National Institutes of Health, Genetic and Rare Diseases Information Centers.

**Including U.S. states, territories, and commonwealths.

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