Nematodes-Phasmids

• Nematodes


  • Strongyloides stercoralis
  • Ancylostoma duodenale
  • Ancylostoma caninum
  • Ancylostoma ceylanicum
  • Ancylostoma braziliense
  • Necator americanus
  • Angiotrongylus cantonensis
  • Enterobius vermicularis
  • Ascaris lumbricoides
  • Toxocara canis
  • Toxocara cati

  
• Ascaris lumbricoides


  Giant Intestinal Roundworm, Most common intestinal nematode of man, Member of the STH: HATS, Member of Unholy Three: HAT, Member of parasites having Heart-Lung Migration: ASH

  
• Habitat


  Small intestine
• Diagnostic stage


  Ova found in stool (fertilized/unfertilized)
• Infective stage


  Embryonated egg
• Mode of Transmission


  Ingestion of embryonated eggs (fecal-oral transmission); embryonated in soil

  
• Vectors


  Flies and cockroaches (mechanical vectors)
• Adult Worm Morphology


  • Pinkish creamy in color when fresh
  • Female worms are longer than male worms
  • Life span is 1-2 years
  • Cylindrical shape with tapering ends
  • Trilobate lips

  
• Egg Morphology


  • Infective 2-6 weeks after deposition
  • Survive harsh environments: dry/freezing temperatures
  • Either fertilized or unfertilized
  • 3 layers: Inner vitelline/lecithin layer, Middle Glycogen layer, Outermost corticated layer (Albumin)
  • Both fertilized and unfertilized egg can be corticated or decorticated

  
• Larval Stages


  • L1-L4
• Life Cycle


  1. Infective stage: Embryonated eggs containing the L2 larvae

  2. Migratory Phase: Eggs hatch, L2 larvae liberated, L2 larvae molt to L3 and penetrate intestine, reach right side of heart via portal circulation, enter lungs via pulmonary capillaries, L3 larvae mature to L4 in lungs, L4 larvae pass into alveoli, migrate via bronchi, trachea and pharynx, swallowed to reach intestine

  3. Intestinal Phase: Larvae develop into adult worms in small intestine

  
• Clinical Symptoms and Pathology due to Migrating Larva

  • Pulmonary symptoms: productive cough, chest discomfort and fever (Loeffler's syndrome/Ascaris pneumonitis)
  • Increased eosinophils: greatest increase in EO: T.aspiralis
  • Charcot-Leyden crystals: eosinophil degradation products
• Clinical Symptoms and Pathology due to Adult Worm

  • Asymptomatic/mild
  • Malnutrition and growth retardation
  • Intestinal complications: large bolus of entangled worms causing acute pain of the abdomen due to bowel obstruction
  • Allergic manifestations: fever and urticaria due to toxic fluid (Ascaron)

  
• Laboratory Diagnosis


  • Egg detection- Stool examination by saline and iodine wet mount: fertilized and unfertilized egg
  • Adult Worms: Xray, USG, Barium meal of GIT, Eosinophilia and Charcot Leyden crystals in sputum and stool
  • Larva: Sputum/Gastric aspirates

  
• Treatment


  • Albendazole
  • Mebendazole
  • Pyrantel pamoate- safe in pregnancy
• Enterobius vermicularis (Oxyuris vermicularis)

  Pinworm, Seatworm, Social worm, Society worm, Has familial or group tendency, active transmission within the household

  
• Habitat


  Large intestine
• Diagnostic stage


  Embryonated egg
• Mode of Transmission


  Inhalation, Ingestion, Autoinfection (External), Sexual transmission
• Adult Worm Morphology


  • Male: does after copulation
  • Female: will go to the perianal region, oviposit, dies or autoinfect

  
• Egg Morphology


  • Oval or planoconvex (one side is plain and the other side is flat because it is compressed laterally)
  • Elongated, flattened on one side, D-shaped; Embryonated
  • Double-layered (Albuminous layer and lipoidal layer; no glycogen layer)
  • Tadpole-like embryo
  • Not bile-stained- colorless in saline amount

  
• Clinical Features


  • Pruritus ani/Nocturnal pruritus
  • Extrainestinal enterobiasis: vagina, uterus, fallopian tube
• Laboratory Diagnosis


  • Microscopy - wet mount of perennial swab collected by cellophane tape method
• Treatment


  • Albendazole
  • Mebendazole
  • Pyrantel pamoate
• Most common helminth to infect man
• Worldwide: E. vermicularis
• Philippines: A. lumbricoides
• Hookworm


  One of the important causes of IDA, 2nd most common helminthic infection reported in humans

  
• Hookworm species infecting man

  • Ancylostoma duodenale (Old World Hookworm; 2 pairs of teeth)
  • Necator americanus (American hookworm/American murderer/New World Hookworm; semilunar cutting plate)
  • Ancylostoma braziliense(Cat hookworm; 2 pairs of teeth)
  • Ancylostoma caninum(Dog hookworm; 3 pairs of teeth

  
• Infective Stage


  L3/Filariform larva (sheathed)

  
• Mode of Transmission


  Skin penetration (direct penetration; e.g. unprotected feet)
• Egg Morphology


  • Ovoidal, thin-shelled and colorless
  • Inside is a germ cell in fragmentation: 2-8 blastomeres
  • "Morula ball formation"

  
• Adult Hookworm Morphology


  • N. americanus: S-Shaped, Semilunar cutting plate
  • A. duodenale: C-Shaped, 2 pairs of teeth
  • Copulatory Bursa: Bipartite (2 digits) for N. americanus, Tripartite (3 digits) and simple, not barbed for A. duodenale

  
• Larval Stages


  • L1-L4
  • L1: rhabditiform larva
  • L3:filariform larva; infective stage to man
  • Rhabditiform larva of A.duodenale and N.americanus are morphologically similar

  
• Larval Morphology


  • L1 Rhabditiform Larva: Short and stout, Open mouth: Feeding stage, Long Buccal cavity, Short/small genital primordium
  • L3 Filariform Larva: Long and slender, Closed mouth: nonfeeding stage, Sheathed, pointed tail

  
• Clinical Features due to Larval Penetration

  • Local lesion: maculopapular dermatitis and rashes (ground itch) at the site of skin penetration
  • Serpiginous tracks: may be formed due to subcutaneous migration of the larva
  • Animal Hookworms A.braziliense and A. caninum: Creeping eruption/cutaneus larva migrans

  
• Clinical Features due to Larval Migration

  • Wakana Disease: pulmonary lesions and hemorrhage
• Clinical Features due to Adult Worms

  • Tissue damage: at the site of attachment (blood loss and anemia)

  
• Laboratory Diagnosis


  • Stool microscopy (DS: Eggs)
  • Harada Mori Culture Technique
• Strongyloides stercoralis


  Threadworm, Smallest nematode infecting man, Facultative nematode: Free living in soil, Parasitic (Female) in Small intestine