Several species of parasitic protozoa are transmitted through water, with Giardia
intestinalis and Entamoeba histolytica/dispar being among the most important
intestinal parasites worldwide. Morbidity, and particularly mortality, rates for E.
histolytica/dispar are high, especially in nonindustrialized countries. More information
on Entamoeba can be found in Volume 2 of the WHO Guidelines for
drinking-water quality. A wide variety of free-living amoebae occur in water, but
only Naegleria fowleri and Acanthamoeba spp. have been identified as pathogenic
for man. N. fowleri may be present in thermally polluted waters and sporadically
causes fatal primary amoebic meningoencephalitis; however, only one outbreak
has been related to a drinking-water supply system (Marshall et al.,1997). Acanthamoeba
spp. can be found throughout the aquatic environment; these organisms
cause sporadic cases of keratitis in wearers of contact lenses after exposure
to contaminated recreational water and contact lens cleaning fluids (Marshall
et al., 1997). Drinking-water taps were identified as the source of contamination
when home-made lens-cleaning solutions were found to contain Acanthamoeba