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<p>Importing text file</p> <p><b>Nová stránka</b></p><div>:Slovak term: [[Slovenský termín]]<br /> # Worm-like stage of development of insects and helminths, which can move and seek food (WHO 1992).<br /> <br /> ==Explanation==<br /> Invertebrate animals are naturally present in many water resources used as sources for the<br /> supply of drinking-water. Small numbers of adults or their larvae may pass through<br /> water-treatment works if the barriers to particulate matter are not completely effective.<br /> Many of these animals can survive and even reproduce within the supply network by<br /> deriving their food from the microorganisms and organic matter in the water or, more<br /> commonly, present in deposits on pipe and tank surfaces (WHO 1992).<br /> <br /> The infective stages of many helminths, such as parasitic roundworms and flatworms, can<br /> be transmitted to humans through drinking-water. As a single mature larva or fertilized egg<br /> can cause infection, these should be absent from drinking-water.<br /> <br /> Only animals that are aquatic for the whole of their life-cycle can colonise the distribution<br /> system and form breeding populations there. This excludes most insect larvae.<br /> Nevertheless, larvae of many species of chironomid may be present in the distribution<br /> system in appreciable numbers. Some pesticides are used for public health purposes,<br /> including the addition to water to control the aquatic larval stages of insects of public<br /> health significance (WHO 1992).<br /> <br /> ==Example==<br /> “The life cycle of fleas has four stages: egg, larva, pupa and adult. Adult fleas are 1-4 mm<br /> long and have a flat narrow body. They are wingless with well developed legs adapted for<br /> jumping. They vary in colour from light to dark brown. The larvae are 4-10 mm long and<br /> white; they have no legs but are very mobile.” (WHO 1992)<br /> <br /> ==References==<br /> * WHO (1992) [http://www.who.int/water_sanitation_health/hygiene/envsan/onsitesan/en/ A guide to the development of on-site sanitation]<br /> <br /> ==Links==<br /> * [http://apps.who.int/thelexicon/ WHO — The Health and Environment Lexicon]<br /> <br /> [[Category:EN]]</div>

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