Which Parasites Are Important for Humans?

(a) Protists/protozoa Unicellular organism and reduced specimens of different origins (b) Helminths Worms, which belong to the animal phyla: Platyhelminthes (flatworms), Nemathelminthes, Aschelminthes (roundworms), Acanthocephala (thornyheaded worms), Annelida (e.g. leeches) or Pentastomida (tongue worms). The members of these different worms range in a size from a few millimetres up to 30 m. (c) Arthropoda The name comes from a Greek term and means “feet with segments”. This worldwide distributed group includes subgroups such as Chelicerata (1⁄4Greek: horny claws, e.g. spiders), insects (1⁄4Latin: animals with a clearly segmented body, e.g. beetles, mosquitoes, bugs, etc.) and Crustacea (1⁄4Latin: animals with a hard body cover, e.g. shrimps, etc.). All members of these groups are characterized by a rather thick body cover containing chitin and often in addition lime components. All this together forms a stiff exoskeleton, the segments of which are interconnected by smooth ligaments thus guaranteeing flexibility. The specimens of this group harm their hosts either directly, e.g. by their sucking activity or by transmission of agents of diseases (viruses, bacteria, fungi and/or other parasites). The exact definition of the systematic position of parasites is very difficult, since the members of the different groups have developed often very sophisticated adaptations, so that even members of the same group may appear and behave completely different. Thus this book considers and presents each group of parasites not in a systematically sense, but just under their morphological