more resistant cysts are sensitive to disinfectants
such as chlorine2-7 and monochloramine,
7,8 which are used for disinfection
of drinking water and swimming pools, if
adequate levels are maintained and monitored.
The chlorine sensitivity is moderate
and in the same range as the cysts from
Giardia intestinalis, another waterborne
pathogen.9,10 Specifically, chlorine at a
concentration of 1 ppm (1 mg/L) added
to 77°F (25°C) clear water at a pH of 7.5
will reduce the number of viable N. fowleri
trophozoites by 99.99% (4 logs) in 12 minutes.
The more resistant N. fowleri cysts are
reduced by 99.99% (4 logs) in 53 minutes
under the same conditions.6
The Louisiana experience led to some
changes (an emergency rule) enacted
within the state to protect people and
ensure that N. fowleri does not survive
within water distribution systems. The
rule requires water systems to maintain
minimum 0.5 mg/L free chlorine residual
and can be adjusted higher based on specific
pH values. If chloramines are used, a
20 SOURCE summer 2014
minimum of 0.5 mg/L is required of the
public water systems. Disinfectant residual
monitoring was also increased 25 percent
higher than what had been required of the
PWS. These additional residual monitoring
samples are to be taken from sites in
low flow areas and extremities in the distribution
system, including the maximum
residence time location, at regular periods
throughout the sampling period. If disinfectant
residual drops below 0.5 mg/L at
any site within the distribution system,
monitoring increases to daily until the
minimum disinfectant residual has been
achieved at the site. S
2 Chang SL. Resistance of pathogenic Naegleria
to some common physical and chemical
agents. Appl Environ Microbiol. 1978;
3 Tiewchaloren S, Junnu V. Factors affecting
the viability of pathogenic Naegleria species
isolated from Thai patients. J Trop Med
Parasitol. 1999; 22:15-21.
4 De Jonckheere J, van de Voorde H. Differences
in destruction of cysts of pathogenic and
nonpathogenic Naegleria and Acanthamoeba
by chlorine. Appl Environ Microbiol. 1976;
31:294-7. (1mg/l for an hour for cysts).
5 Cursons RT, Brown TJ, Keys EA. Effect
of disinfectants on pathogenic free-living
amoebae: in axenic conditions. Appl Environ
Microbiol. 1980; 40:62-66.
6 Sarkar P, 6 Gerba C. Inactivation of Naegleria
fowleri by chlorine and ultraviolet light. J
AWWA. 2012; 104:51-2.
7 Robinson BS, Christy PE. Disinfection of
water for control of amoebae. Water. 1984;
8 Ercken D, Verelst L, Declerck P, Duvivier L,
Van Damme A, Ollevier F. Effects of peracetic
acid and monochloramine on the inactivation
of Naegleria lovaniensis. Water Sci Technol.
9 Jarroll EL, Bingham AK, Meyer EA. Effect
of chlorine on Giardia lamblia cyst viability.
Appl Environ Microbiol. 1981;41:483-7.
10Rice EW, Hoff JC, Schaefer FW 3rd. Inactivation
of Giardia cysts by chlorine. Appl
Environ Microbiol. 1982; 43:250-1.
Future Challenges, continued from page 18