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Nematode

The intestinal nematodes Ascaris Hook worms Pin worm Whip worm. The blood- and tissue dwelling nematodes The filaria Trichinella . Nematode. Ascaris 蛔虫. Ascaris lumbricoides 似蚓蛔线虫. Introduction. The first representative and the most common intestinal parasite

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Nematode

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  1. The intestinal nematodes Ascaris Hook worms Pin worm Whip worm The blood- and tissue dwelling nematodes The filaria Trichinella Nematode

  2. Ascaris蛔虫 Ascaris lumbricoides 似蚓蛔线虫

  3. Introduction • The first representative and the most common intestinal parasite • Cosmopolitan in distribution • Rural > urban • Children > adults

  4. Morphology Adult Looks like an earthworm Female (20-35 cm); Male (12-30 cm) 3 lips which carry minute teeth

  5. A pair of female and male worms of A. lumbricoides. Notice the vulvar waist(arrow)of the female worm and the coiled end of the male worm.

  6. Ascaris female worm

  7. A scanning electron micrograph of Ascaris showing the three prominent “lips”

  8. Egg • Fertilized egg • Unfertilized egg

  9. Egg shell Ovum Albuminous layer A. lumbricoides, fertilized egg (6050 micrometer)

  10. A. lumbricoides, fertilized egg

  11. A. lumbricoides unfertilized egg 

  12. The life cycle of A. lumbricoides

  13. Living site Adults in small intestine HOST MAN Migration Larvae migrate though the lungs Diagnostic stage Undeveloped eggs in feces Method of infection Infective eggs are ingested Infective stage Eggs embryonate in soil by 2-3 wks

  14. Symptomatology Larva Pneumonitis Asthma attacks Loeffler’s syndrome

  15. Adult • The presence of few worms may be asymptomatic (85%) • The most common symptoms are vague abdominal pain • Large numbers of worms may cause malnutrition and present signs and symptoms of obstruction

  16. Migration of adult worms may cause signs and symptoms of perforation, peritonitis, appendicitis or extrahepatic biliary obstruction.

  17. A.lumbricoides in common bile duct

  18. Cross section of a liver specimen contains many adult worms of A.lumbricoides obstructing the intrahepatic and extrahepatic bile ducts.

  19. Ascarid chronic pancreatitis

  20. A large mass of Ascaris lumbricoides that was passed from the intestinal tract.  The ruler at the bottom of the image is 4 cm (about 1.5 inches) in length.

  21. An autopsy specimen shows intestinal obstruction by many adult worms of A.lumbricoides. Notice the markedly distended intestinal loop, the thin intestinal wall with hemorrhage and worms protruding from the perforated wound.

  22. Peritonitis caused by intestinal perforation due to Ascaris Resected bowel and the adult female from the peritoneal cavity

  23. Diagnosis • Microscopic identification eggs in the stoola direct wet mount examination of the specimen (200,000 eggs/female/day) • Macroscopic identification of adults passed in stool or through the mouth or nose

  24. Epidemiology • Worldwide distribution, throughout the temperate and tropical areas • 1,000,000,000 people in the world • 40% population in Africa and Asia • 600,000,000 in China (1992)

  25. Treatment • Albendazolea single oral dose of 400 mg • Mebenazole100 mg orally twice daily for 3 days

  26. Prevention • Avoid contacting soil that may be contaminated with human feces • Do not defecate outdoors • Dispose of diapers properly

  27. Wash hands with soap and water before handling food • When traveling to areas where sanitation and hygiene are poor, avoid water or food that may be contaminated • Wash, peel or cook all raw vegetables and fruits before eating

  28. Hook worms钩虫

  29. Ancylostoma duodenale十二指肠钩口线虫Necator americanus美洲板口线虫

  30. Pinworm蛲虫Enterobius vermicularis蠕形住肠线虫

  31. Whip worm鞭虫Trichuris trichiura毛首鞭形线虫

  32. Adult worms of Ancylostoma duodenale

  33. Adult worms of Necator americanus

  34. Morphology • Adult • Cylindrical with the head bent sharply backwards • Males are smaller than the females and possess a bursa at their posterior end

  35. Scanning electron micrograph of the oral opening of Ancylostoma duodenale, another species of human hookworm.  Note the presence of four cutting "teeth," two on each side.

  36. Adult mouthpart of Necator americanus Note : The large buccal capsule is open dorsally with one pair of cutting plateteeth.

  37. Bursa of hookworms Lift A. duodenale; Right N. americanus

  38. Enterobius vermicularis adult female 0.8-1.3cm.in length , spindle-shaped with a long thin sharply tail. The greater part of the body is occupied by the uterus filled with eggs.

  39. Trichuris trichiura adults. 

  40. Egg (indistinguishable between the 2 species) • Median size (like the ascaris egg) • Elliptical • Transparent • Thin shell • 4-cell stage when discharge

  41. Enterobius vermicularis egg. Note the thick shell and characteristic shape; approximate length = 55 µm.

  42. Egg < Ascaris egg Non-symmetrical ellipse; D shaped Transparent Thick transparent shell Tadpole-like embryo when discharged

  43. Trichuris vulpis egg

  44. Life Cycle • Host -man • No intermediate host 钩虫: Egg Larva (free-living) Larvae migrate fromskin to the lungs 蛲虫:Egg takes 6 hours to be infective stage 鞭虫: Similar to Ascaris but no pulmonary migration . There are reservoir hosts.

  45. Parasitic site: 蛔虫: small intestinal 钩虫: upper small intestine; Duodenum, jejunum 蛲虫: colon Gravid female adult deposits its eggs on the anus and perianal skin. 鞭虫: ileo-caecal region

  46. Infection stage 蛔虫: infective egg 钩虫: infective larva 蛲虫: infective egg ( Egg takes 6 hours to be infective stage) infective mode: Anus-Hand-Mouth Auto-infection/Cross-infection 鞭虫: infective egg

  47. Pathogenic stage: 蛔虫: adult worm /larva 钩虫:adult worm Digestive disturbances /Allotriophagy Microcytic hypochromic anemia (sucking, oozing, discharging)A.d. 0.15-0.4ml/d; N.a. 0.02-0.1ml/d larva:Dermatitis ‘ground itch’ Pneumonitis and Bronchitis

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