1. Significance
Naegleria fowleri are free-living thermotolerant amoebae prevalent in warm fresh water throughout the world. Thermotolerant amoebae are defined as amoebae that can thrive at elevated temperatures (42–45 °C). In 1965, Fowler and Carter identified N. fowleri in fresh water as the cause of primary amoebic meningoencephalitis (PAM) in Australia.1 Following this, N. fowleri was isolated in drinking water in Australia in the 1970s. Naegleria fowleri was not known to be a problem in the United States drinking water supply until recently, as historical PAM cases were primarily caused by exposure to fresh water lakes and rivers during recreational use.2 In 2002, two children died from exposure to N. fowleri while bathing in water from an unchlorinated well in the Phoenix, AZ metropolitan area.3 In 2011, two individuals in Louisiana died from PAM after using tap water in neti pots for nasal irrigation.4 A third person in Louisiana died in 2013 after contracting PAM from tap water used on a backyard water slide.5 In 2012, a 47-year old male from the U.S. Virgin Islands contracted N. fowleri from tap water used for ablution.6 Ritual nasal rinsing is likely a major route of exposure.
Naegleria fowleri inhabit surface water, ground water, and hot springs, but can also persist in drinking water that contains little or no disinfectant residual, including drinking water distribution systems, premise plumbing, cisterns, roof top collection vessels (e.g., rainwater tanks), treated aquatic venues (e.g., pools, hot tubs, and water playgrounds), and decorative water fountains. Evidence also indicates that thermotolerant amoebae are important in the transport and propagation of the human pathogenic bacteria Legionella pneumophila and nontuberculous mycobacteria.7,8