Brief Summary
Naegleria fowleri is a free-living amoeba commonly found in warm freshwater
environments such as hot springs, lakes, natural mineral waters, and resort spas
frequented by tourists. These amoebae can tolerate temperatures of up to 45 C.
Infection with this parasite can cause primary amoebic meningoencephalitis
(PAM), an acute and generally fatal disease of the central nervous system that
has a rapid onset and typically results in death within a week or less. Although
PAM is generally viewed as a very rare condition, the number of reported PAM
cases is increasing each year. PAM is difficult to diagnose because the clinical
signs of the disease are similar to those of bacterial meningitis.
Because it typically presents in healthy individuals, N. fowleri is not
categorized as an opportunistic amoeba, as are Acanthamoeba and Balamuthia, but
rather as a pathogen. PAM often occurs in healthy immunologically intact
children and young adults who were exposed during recreational activity in warm
bodies of freshwater. Typically, PAM occurs in the hot summer months, when large
numbers of people engage in recreational aquatic activities in freshwater bodies
that may harbor these amoebae.
Naegleria fowleri amoebae enter the human host via the nasal route when they are
splashed or inhaled into the nose. Forcing water into the nose by diving or
jumping into water is common, but N. fowleri can become motile even if the
victim is simply submerged under water. Upon entering the nasal cavity, N.
fowleri infect the olfactory mucosa and ascend the olfactory nerve through the
cribiform plate until they reach the olfactory bulbs of the central nervous
system.
Naegleria fowleri occurs worldwide and has been isolated from soil and fresh
water. More than 30 species of Naegleria have been described based on the
sequence of the SS rRNA gene, but only N. fowleri is known to cause infection in
humans. In nature, these amoebae feed upon bacteria and have been isolated from
freshwater pools, puddles, lakes, rivers, swimming pools, hot springs, thermally
polluted effluents of power plants, hydrotherapy pools, aquaria, sewage,
irrigation canals, and even from the the nasal passages and throats of healthy
individuals. However, they have not been recovered from seawater.
Naegleria fowleri has been found in aquatic environments frequented by tourists
inThailand and Japan, in swimming areas along rivers in Italy, in swimming pools
and streams in Belgium and the former Czechoslovakia, in swimming pools in
England and New Zealand, in hot springs in California and New Zealand, and in
warm freshwater lakes throughout the southern United States.
Visvesvara et al. (2007) reviewed the diagnosis and pathophysiology of N. fowler
infection, as well as public health strategies for monitoring and control.
Heggie (2010) reviewed the epidemiology, diagnosis, pathophysiology, and
treatment of N. fowler infection.
(Visvesvara et al. 2007; Heggie 2010 and references therein; Centers for Disease
Control Parasites and Health website)