|
Helminths (), also commonly known as parasitic worms, are large multicellular organisms, which when mature can generally be seen with the naked eye. They are often referred to as intestinal worms even though not all helminths reside in the intestines; for example schistosomes are not intestinal worms, but rather reside in blood vessels. There is no clear consensus on the taxonomy of helminths; it is more of a commonly used term to describe certain worms with superficial similarities. These are flatworms (plathelminths) cestodes and trematodes, and (roundworms) nemathelminths (nematodes) - both of these are parasitic worm types – and the annelida, which is not parasitic or at the most ectoparasites like the leeches.〔Samuel, B. (Ed) (1996). (Medical Microbiology, 4th Edition ). University of Texas Medical Branch, Galveston, Texas〕 Many, but not all, of the worms referred to as helminths belong to the group of intestinal parasites. An infection by a helminth is known as helminthiasis, soil-transmitted helminthiasis, helminth infection or intestinal worm infection. The same naming convention applies to all helminths whereby the ending "-asis" (or in veterinary science the ending "-osis") at the end of the name of the worm is added to signify the infection with that particular worm, for example ''Ascaris'' is the name of a particular helminth, and ascariasis is the name of the infectious disease caused by this helminth. Helminths are worm-like organisms living in and feeding on living hosts, receiving nourishment and protection while disrupting their hosts' nutrient absorption, causing weakness and disease. Those that live inside the digestive tract are called intestinal parasites. They can live inside humans and other animals. In their adult form, helminths cannot multiply in humans. Helminths are able to survive in their mammalian hosts for many years due to their ability to manipulate the immune response by secreting immunomodulatory products.〔Jirillo, E., Magrone,T., Miragliotta, G. (2014). (Immunomodulation by Parasitic Helminths and its Therapeutic Exploitation ). In: Pineda, M.A., Harnett, W. (Eds), Immune Response to Parasitic Infections (Vol 2, pp 175-212), Bentham eBooks, DOI: 10.2174/97816080598501140201, ISBN 978-1-60805-985-0〕 Helminth ova (or eggs) have a strong shell that protects the eggs against a range of environmental conditions. Helminthology is the study of parasitic worms and their effects on their hosts. The word helminth comes from Greek ''hélmins'', a kind of worm. == Taxonomy == There is no real consensus on the taxonomy (or groupings) of the helminths, particularly with the nematodes. The term "helminth" contains a number of phyla, many of which are completely unrelated. However, for practical considerations the term is still used nowadays to describe four groups with superficial similarities, the phyla Annelida, Platyhelminths, Nematoda and Acanthocephala.〔 There is in fact no helminth classification, it is an “artificial” term. The most important helminths in the sanitation field are the human parasites, which is why most people relate the term helminth to them, where they are classified as nemathelminthes (nematodes) and platyhelminthes, depending on whether they possess a round or flat-shaped body respectively. The latter are further divided into cestodes and trematodes depending on whether or not they have a segmented body.〔Maya, C., Torner-Morales, F.J., Lucario, E.S., Hernández, E., Jiménez, B. (2012). (Viability of six species of larval and non-larval helminth eggs for different conditions of temperature, pH and dryness ). Water Research, Vol 46, No 15, pp 4770–4782, doi:10.1016/j.watres.2012.06.014〕 Ringworm (dermatophytosis) is actually caused by various fungi and not by a parasitic worm. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「helminths」の詳細全文を読む スポンサード リンク
|