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Nematodes ( 线 虫 )

Nematodes ( 线 虫 ). Content: I. Introduction II. Ascaris lumbricoides （蛔虫） III. Trichuris trichiura （鞭虫） IV. Enterobius vermicularis （蛲虫） V. Hookworms （钩虫 ) VI. Trichinella spiralis （旋毛虫） VII. Filariar （丝虫）. I. Introduction to Nematode. Medical Parasitology

colleen-liddane
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Nematodes ( 线 虫 )

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  1. Nematodes (线 虫) Content: I. Introduction II. Ascaris lumbricoides（蛔虫） III. Trichuris trichiura（鞭虫） IV. Enterobius vermicularis（蛲虫） V. Hookworms（钩虫) VI. Trichinella spiralis（旋毛虫） VII. Filariar（丝虫）

  2. I. Introduction to Nematode Medical Parasitology ProtozoaHelminths Arthropoda Trematoda Nematode Cestoidea Acanthocephala ( 吸虫) ( 线 虫） （绦 虫 ） （棘头虫） Ascaris lumbricoides, Trichuris trichiura, Enterobius vermicularis Hookworms, Trichinella spiralis, Filariar

  3. 1. Morphology of nematodes 1) General morphology (1) Tubular in shape and bilaterally symmetrical (2) With a complete digestive canal (3) Adult worm separated in male and female

  4. 2) Body wall The body wall of nematodes is covered: • Cuticle （角皮层） • Hypodermis （皮下层） • Musculature （肌层）

  5. Cuticle formed some special constructions, they have special functions and are very important to identify the species of nematodes for examples: Buccal capsule (口囊) Copulatory bursa (交合伞) Spicule (交合刺) Alae (翼） Papillae (乳头）

  6. alae papillae Spicule copulatory bursa(交合伞)

  7. 3) Digestive system It is complete with mouth, esophagus, intestine and anus

  8. 4) Reproductive system Most nematodes are separated in male and female (1) male reproductive system Testis seminal vesicle (睾丸） （储精囊） vas deferens ejaculatory duct （输精管） （射精管）

  9. (2) Female Reproductive System Most females usually have two ovaries,oviducts and uterus.. ovary—oviduct —uterus.. vagina-vulva ovary—oviduct —uterus.. （阴道） (阴门） （卵巢） （输卵管） （子宫）

  10. 5) Reproductive mode • Oviparous (卵生) • Ovoviviparous (卵胎生）

  11. 2. Life cycle The four juvenile stages and ecdysis (molting of cuticle 蜕皮）. ecdysis Eggs Larvae(4 stages) adults (male & femal)

  12. 6) egg：the shell consists of 3 layers Vitelline layer (卵黄膜), Chitinous layer (壳质层) Ovum or embryo Lipid layer (蛔甙层)

  13. Kinds of life cycle in nematodes • Direct life cycle: in which the parasite is passed from host to the next through the contaminated food or water. Intermediate host is not necessary to these parasites Ascaris lumbricoides Trichuris trichiura Enterobius vermicularis Hookworms

  14. 2) Indirect life cycle: intermediate host is necessary in this style of life cycle Trichinella spiralis Filaria

  15. 3. Pathology 1)Larvae： ( 1) dermatitis caused by cutaneous invasion and subcutaneous migration of larva; ( 2) injury to organs or tissues by migration of larvae in the body

  16. 2) Adults： (1) injury to intestinal mucosa caused by the parasites living in gastro- intestinal system (2) injury to lymphatic system, muscles or nervous system caused by the parasites living in tissues

  17. Ascaris lumbricoides (蛔虫) The common name of Ascaris lumbricoides is “round worm”，it is the largest nematode and the adults live in intestine of human, cause Ascariasis (蛔虫病)； The morbidity in whole world is estimated at 1 billion , the infective rate of the population in China is about 44.9% to 71%； The round worms of cat (Toxocara cati) and dog (Toxocara canis) can result in larval migrans in human

  18. 1. Morphology 1) The largest of intestinal nematode; resembling an earthworm; living worms show reddish colour; 2) Three lips around the mouth in “品”type and possess small teeth

  19. Comparison of different nematodes in size

  20. 3）How to identify male and female • Male: measuring 25cm long， posterior extremity curved in the form of a hook • Female: measuring 35cm long, posterior extremity is straight

  21. 4) How to identify the eggs: • Fertilized eggs are oval to round, the shell is thick and with protein coat (蛋白质膜). An ovum in the shell. • Unfertilized egg is more elongated, thinner shell with small protein coat and an atrophied ovum marked by refractile granules. refractile granules Protein coat ovum Chitin layer Fertilized egg losing of protein coat Fertilized egg Unfertilized egg

  22. Resistance of eggs to chemicals The resistance of Ascaris eggs to chemicals is very strong. They can embryonate successfully in 10﹪ formalin, potassium dichromate (KCl), hydrochloric acid (HCl), nitric acid, acetic acid, and sulfuric acid(H2SO4) This extraordinary chemical resistance is the result of the lipid layer of the eggshell

  23. 3. Life cycle moist、shady warm, O2, 2w 240000/day （feces） ingest (hatch in up small intestine） eggs adults (intestine） infective eggs eggs penetrate intestine wall —blood—liver—right heart — lungs—respiratory tree—pharynx —intestine larvae Adults (intestine) Larvae migrate in the circulation system

  24. 4. Pathology • larvae: • Ascaris Pneumonitis :caused by the penetration of larvae in lung’s capillaries During the pulmonary stage, there may be a brief period of cough, fever, expectoration (咳痰) , sputum with blood • Asthma:caused by the metabolites of the parasites

  25. Ascaris lumbricoideslarva in section of lung

  26. 2) Adults： (1) Malnutrition: adults take liquid contents of intestine as their food; damage of mucosa of intestine causing malabsorption (2) Disorder of digestive system: abdominal pain anorexia (食欲不振) nausea (恶心) vomiting (呕吐) diarrhea (腹泻) intestinal obstruction .

  27. 3）Allergic responses to metabolites produced by the worms • rashes(荨麻疹) • Asthma • Restlessness（烦躁不安） • insomnia(失眠) • angioneuro-edema(血管神经性水肿) • optic neuritis (视神经炎) • Conjunctivitis ( 结膜炎)

  28. 4）Complication(并发症)： • Adults have a special characteristic----”penetration of hole” • Cause many different complications due to the penetration

  29. (1) penetrate to the appendix and causes appendicitis (2) penetrate to the pancreatic and bile ducts cause grave results. Ascaris in pancreas and bile duct

  30. Empyema of chest Adults in bile duct detected by B-ultrasound

  31. (3) intestinal obstruction caused by massive infection

  32. (4) Worms reaching the stomach often cause nausea (5) Worms that reach the esophagus may crawl into the trachea, causing suffocation （窒息） (6) They may crawl into the middle ears, causing extensive damage (7) They may simply exit through the nose or mouth

  33. 5. Diagnosis • By identifying the adults passed • By identifying the eggs in the feces

  34. 6. Epidemiology and control 1. Epidemiology: this disease is very widespread Worldwide over 1 billion persons are infected. 44.9% to 71% of population are infected with the parasite in China Why?

  35. Profuse production of eggs (? / per day,per female) • Egg’s resistance to chemical and environmental condition;remains viable for about 1 year in the field • Nightsoil is used as fertilizer • Low personal hygiene (3F) • Poor sanitation

  36. 2)Treatment and Prevention: • Mebendazole（甲苯达唑）： 200 mg, for adults and 100 mg for children, for 3 days is effective. • Albendazole（阿苯达唑）： 400mg/d，1~2d • Good hygiene is the best preventive measure

  37. Trichuris trichiura (毛首鞭形线虫) 1. Introduction: The common name of Trichuris trichiura is whip-worm(鞭虫), adults live in caecum (盲肠) of human and result in trichuriasis(鞭虫病)

  38. 2. Morphology: 1) Adults resemble a whip, anterior with a hair-like lash and posterior with the handle. Mouth cavity is provided with a minute spear 2) Male: about 4 cm long, posterior is spirally coiled. 3) Female: about 5 cm long, posterior extremity straight.

  39. 4)Egg • A typical barrel shape with two polar plugs (2) Size: 50-54 µm by 22-23 µm  (3)The external layer of the shell of the egg is yellow brown (4) An ovum is in the egg when it passed with stool

  40. 3. Life cycle 1T~7T/daily moist、warm 3~5w adults （cecum） eggs infective eggs migration down cecum ingestion larvae （small intestine） adults （cecum） Larvae do not enter circulation system！

  41. 4. Pathology • Feeding on tissue fluid and blood; • The slender anterior ends penetrate into the gut mucosa and make lesions;

  42. Symptoms: Symptoms are determined largely by the worm burden: • light infections are asymptomatic. • Heavier infections are characterized by: 1) chronic mucous and bloody diarrhea 2) abdominal pains 3) hemorrhage and anemia (贫血) or rectal prolapse (直肠脱垂) in heavy infection children 4) The infection may result in malnutrition and growth retardation

  43. 5. Diagnosis • Diagnosis is based on symptoms and the presence of eggs in feces

  44. 6. Prevalence and control • Trichuriasis often prevail with ascariasis • 17.38% of population infected with this parasite in China • The treatment and control can refer to ascariasis

  45. Hookworm (钩虫） Adults live in the intestine and take blood from the host, cause hookworm disease

  46. Species of Hookworm • Human hookworms: 1) Ancylostoma duodenale (十二指肠钩口线虫, 十二指肠钩虫) 2) Necator americanous (美洲板口线虫, 美洲钩虫） • Animal hookworms: 1) Ancylostoma ceylanicum (锡兰钩口线虫) 2) Ancylostoma caninum (犬钩口线虫) 3) Ancylostoma braziliense(巴西钩口线虫) (caused cutaneous larval migrans)

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