寄生虫大题（英文）.docVIP

Parasites harms on man (1)Depriving the host of nourishment: example, hookworms suck blood. (2)Mechanical effects of parasites on host tissues and organs: example, biliary ascariasis and larva migrans. (3)Toxic effect: Arthropods introduce toxin into the host skin, inducing the host local and systemic reactions. Example, mosquitoes, spiders and ticks introduce venom when they insert their mouth parts into the skin. (4)Immuno-pathological lesion: example, schistosoma liver cirrhosis; when hydatid fluid is released from the rupture of a hydatid cyst anaphylaxis often results. 2. Characteristics of Class Nematode (1)Body is non-segmented, elongate, and circular in cross-section. (2)Two sexes are separated. ♀is larger with a straight tail and a double set of reproductive organs. ♂is smaller with a curled tail and a single set of reproductive organs. (3)Digestive tract (system) is complete. (4)The body cavity is a protocoele(原体腔). (5)Life cycle: infective stage is embryonated egg or larva3. Egg→larva (several stages)→adolescent→adult Factors favoring the ascarid spread (1)Simple life cycle. (2)Enormous egg production ( 240,000 eggs/ day/ female ). (3)These eggs are highly resistant to ordinary disinfectants( due to the ascroside). The eggs may remain viable for several years. (4)Social customs and living habits. (5)Disposal of feces is unsuitable. Enterobius vermicularis(pinworm)[An clinical case] The major symptom is anal itch, which is associated with the noctural migration of the gravid females from the anus and deposition of eggs in the perianal folds of the skin. Diagnosis: Cellophane tape technique is first choice. The examination should be made in the morning, before the patient has washed the anus or defecated. Drugs: Albendazole or mebendazole are very effective. Since life span of pinworm is about one mouth, the major problem is re-infection. Repeated treatment may be necessary for a radical cure. 5. Life cycle of a