Helminth parasites platyhelminths

This chapter contrasts the parasitic platyhelminths and parasitic nematodes, and emphasizes selected well-studied species as representative of each phylum (trematodes Fasciola hepatica and Schistosoma mansoni cestodes Hymenolepsis diminuta nematodes Ascaris suum). Supplementary information about the free-living nematode Caenorhabditis elegans and other parasitic helminths is also presented. 

The major anatomical components of the nervous system of parasitic platyhelminths are shown in the generalized schematic of Fig. 14.1. Pax and Bennett (1) have reviewed information regarding putative signaling substances in parasitic helminths see Table... 

Helminth parasites infect a broad range of species, including man and it is estimated that a third of the global population is infected with parasitic worms. In this chapter, we focus solely on parasitic helminths, which have a medical significance to humans. These species include the Digenean flukes of the Class Trematoda (Flatworms) and the Class Cestoda (Tapeworms), both of the phylum Platyhelminthes and the phylum Nematoda (Roundworms). Some of the major species of helminths of medical importance to humans are outlined in Table 1, presented with an arbitrary ranking based on prevalence of worldwide infections. 

Barrett J (1981) Biochemistry of parasitic helminths, Macmillan, London Barrett J, Beis I (1982) Catalase in free-living and parasite platyhelminths. Experientia 38 536 Barron MG, Gedutis C, James MO (1988) Pharmacokinetics of sulphadimethoxine in the lobster, Homarus americanus, following intrapericardial administration. Xenobiotica 18 269-276 Barron MG, James MO (1988) Fate of sulfadimethoxine in the lobster, Homarus americanus. Mar Env Res 24 85-88... 

Worms are known as helminths and the majority is not parasitic. Classes of worms that parasitize man are round worms (nematodes) and flat worms (platyhelminths). The flat worms are divided into tapeworms (cestodes) and flukes (trematodes). Only a few human parasitic worms are common in the United Kingdom, for example threadworms and round worms. In tropical and subtropical parts of the world, where abundant water and high temperatures provide an optimal environment for the larvae and intermediate hosts, parasitic worms are common and widespread. Table 9.8 lists some parasitic worms that can infect man, their effect and drugs used to treat them. 

Helminths constitute a major health problem in humans and domestic animals, especially in the tropical and sub-tropical areas of the world. They are classified in two phyla the flatworms (Platyhelminthes), comprising the flukes (or trematodes) and the tapeworms (or cestode), and the roundworms or nematodes (Nemathelminthes). Most nematodes are not parasitic, but some infect vertebrates by entering the digestive tracts of animals where they develop into adults. Diseases caused by infection are dependent on the residence site of the adult nematode the gastrointestinal tract or body tissues. 

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