Acanthamoeba: background document for the WHO guidelines for drinking-water quality
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World Health Organization
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ii, 8 p.
This background document supports the WHO Guidelines for drinking-water quality by reviewing the characteristics, occurrence and public health significance of Acanthamoeba in drinking-water systems and environmental waters. It describes the biology, ecology and epidemiology of these free-living amoebae, which are widespread in freshwater, soil, drinking-water distribution systems and premise plumbing. The document outlines the two life stages of Acanthamoeba—trophozoites and highly resistant cysts—and summarizes the diseases associated with infection, including acanthamoebic keratitis, granulomatous amoebic encephalitis and cutaneous infections. Particular emphasis is placed on the risk of eye infections among contact lens users exposed to contaminated water. The publication summarizes evidence on the persistence, survival and growth of Acanthamoeba in water, including within biofilms where the organism may be protected from disinfectants. It emphasizes that Acanthamoeba is not transmitted through ingestion of drinking-water, but that exposure to non-sterile water during cleaning or storage of contact lenses represents an important route of transmission. The document also reviews available culture-based and molecular detection methods and discusses prevention and management measures within water safety plans, including effective filtration, control of biofilm formation, protection of distribution systems from contamination and maintenance of disinfectant residuals. It further notes that Escherichia coli is not a suitable indicator for assessing the possible presence or absence of Acanthamoeba in drinking-water because the organism is environmental and capable of persistence and growth in water systems.
This background document supports the WHO Guidelines for drinking-water quality by reviewing the characteristics, occurrence and public health significance of Acanthamoeba in drinking-water systems and environmental waters. It describes the biology, ecology and epidemiology of these free-living amoebae, which are widespread in freshwater, soil, drinking-water distribution systems and premise plumbing. The document outlines the two life stages of Acanthamoeba—trophozoites and highly resistant cysts—and summarizes the diseases associated with infection, including acanthamoebic keratitis, granulomatous amoebic encephalitis and cutaneous infections. Particular emphasis is placed on the risk of eye infections among contact lens users exposed to contaminated water. The publication summarizes evidence on the persistence, survival and growth of Acanthamoeba in water, including within biofilms where the organism may be protected from disinfectants. It emphasizes that Acanthamoeba is not transmitted through ingestion of drinking-water, but that exposure to non-sterile water during cleaning or storage of contact lenses represents an important route of transmission. The document also reviews available culture-based and molecular detection methods and discusses prevention and management measures within water safety plans, including effective filtration, control of biofilm formation, protection of distribution systems from contamination and maintenance of disinfectant residuals. It further notes that Escherichia coli is not a suitable indicator for assessing the possible presence or absence of Acanthamoeba in drinking-water because the organism is environmental and capable of persistence and growth in water systems.