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The Parasites of Medical Importance
Chapter 23
Protozoans and Helminths
Parasitology
n the study of eucaryotic parasites, protozoa and helminths
n cause 20% of all infectious diseases n less prevalent in industrialized countries
Protozoa Protozoa
n singlecelled, animallike microbes, having some form of motility
n life cycles vary q most propagate by simple asexual cell division of the active feeding cell (trophozoite)
q many undergo formation of a cyst q others have a complex life cycle that includes asexual & sexual phases
Helminths Helminths
n adults are large, multicellular animals with specialized tissues & organs
n adult worms mate & produce fertilized eggs that hatch into larvae that mature in several stages to adults
n the sexes may separate or hermaphroditic n adults live in the definitive host n eggs & larvae may develop in the same host, external environment of intermediate host
n a transport host experiences no parasitic development
Helminths Helminths
n pathology arises from worms feeding on & migrating through tissues and accumulation of worms & worm products
n antihelminthic drugs paralyze their muscles, causing them to be shed or interfere with metabolism, killing them
Nematodes Nematodes - - roundworms roundworms
n Filamentous with protective cuticles, circular muscles, a complete digestive tract, & separate sexes
n Ascaris lumbricoides n Trichuris trichiura n Enterobius vermicularis –pinworm n Hookworms n Strongyloides stercoralis n Trichinella spiralis n Filarial worms
Hookworms Hookworms
Trematodes Trematodes or flukes or flukes
n flatworms with ovoid leaflike bodies n have digestive, excretory, neuromuscular, & reproductive systems
n lack circulatory & respiratory systems n animals such as snails or fish are usually the intermediate hosts & humans are the definitive hosts
Cestodes Cestodes- -Tapeworms Tapeworms
n flatworms n long, very thin, ribbonlike bodies composed of sacs (proglottids) & a scolex that grips the intestine
n each proglottid is an independent unit adapted to absorbing food & making & releasing eggs
n Taenia saginata n Taenia solium