nematodes

• Nematodes


  • Also known as 'roundworms'
  • Elongated, cylindrical, and bilaterally symmetrical
  • Unsegmented
  • Has complete digestive system
  • No circulatory system
  • Dioecious (they have separate sexes and can only be male or female, never both)
  • Some are parthenogenic (parasites that may or may not require males for reproduction)
• Male nematodes


  • Smaller
  • Curved posterior
  • Has spicule
• Female nematodes


  • Larger
  • Pointed posterior
  • No spicule
  • Produces eggs (oviparous, oviviparous, or viviparous/larviparous)
• Chemoreceptors


  • Amphids (cephalic chemoreceptors found in all nematodes)
  • Phasmids (caudal chemoreceptors)
• Phasmids (Subclass Secernentia)


  • With caudal chemoreceptors
  • All nematodes except T. trichiura, C. philippinensis, and T. spiralis
• Aphasmids (Class Adenophorea)


  Without caudal chemoreceptors
• Intestinal nematodes habitat


  • Small intestine: C. philippinensis, A. lumbricoides, S. stercoralis, Hookworms, T. spiralis (adult)
  • Large intestine: E. vermicularis, T. trichiura
• Extraintestinal nematodes habitat


  • Muscle: T. spiralis (larva)
  • Lymph nodes & subcutaneous tissues: Filarial worms
  • Eyes & meninges: A. cantonensis
• Basic developmental cycle


  1. Egg

  2. L1 (Rhabditiform larva)

  3. Molting

  4. L2 (Rhabditiform larva)

  5. Molting

  6. L3 (Filariform larva)

  7. Molting

  8. L4

  9. Molting

  10. Adult
• Molting


  When a newly hatched larva, who feeds on bacteria, outgrows and is constrained by its cuticle
• Synthesis


  When a larva creates a new cuticle while within its old cuticle
• Exsheathement


  The casting off of the old cuticle
• Ascaris lumbricoides


  • Most common intestinal parasite in humans in the Philippines
  • Largest intestinal nematode
• Ascaris lumbricoides eggs


  • Adults lay 200,000 eggs per day
  • Become infective 2-6 weeks after deposition
  • Can survive harsh environments (dry/freezing temperatures)
  • Size: Length 85-95 micrometers, Width 38-45 micrometers
  • Egg shell layers: Inner vitelline membrane, Middle glycogen layer, Outermost mammillation
• Stages of Ascaris egg

  • Unfertilized
  • Fertilized corticated
  • Fertilized decorticated
  • Embryonated
• Ascaris lumbricoides adult worm

  • Female: Larger, Pointed posterior tail
  • Male: Smaller, Curved posterior tail
• Ascariasis pathology


  • Ascaris pneumonitis (Loeffler's pneumonia, increased eosinophils, Charcot-Leyden crystals)
  • Visceral Larva Migrans (VLM) due to non-human parasites
  • Erratic migration and obstruction by bolus formation
• Trichuris trichiura


  Adult worm: Anterior 3/5 attenuated for pin-fashion attachment, Male has curved posterior, Female has pointed posterior
• Trichuris trichiura eggs


  • Adults lay 100,000 eggs per day
  • Mucoid prominent bipolar plugs
  • Shape: Japanese lantern/football/barrel/lemon-shaped
  • Color: Yellow-ish brown
  • Size: Length 50-55 micrometers, Width 25 micrometers
• Trichuriasis pathology


  Bloody diarrhea, Epigastric pain, Iron deficiency anemia, Rectal prolapse, Hypoalbuminemia
• Enterobius vermicularis


  • Most common intestinal nematode in humans in the U.S.A.
  • Other names: Oxyuris vermicularis, Threadworm (no longer used)
  • Adult males usually die after copulation
• Enterobius vermicularis transmission


  • Ingestion, Inhalation, Retroinfection, Autoinfection
• Enterobius vermicularis eggs


  • Adults lay 15,000 eggs per night
  • Incubation to become infective is 4-6 hours
  • Oval shaped, flattened on one side, with double-layered shell
  • Size: Length 48-60 micrometers, Width 20-35 micrometers
• Enterobius vermicularis adult worm

  • Female: Gravid uterus filled with eggs, Pointed posterior, Has cephalic alae
  • Male: Flask-shaped/bulb-like esophagus, Curved posterior, Has cephalic alae
• Intestinal nematodes summary


  • Ascaris lumbricoides
  • Trichuris trichiura
  • Enterobius vermicularis
  • Capillaria philippinensis
  • Ancylostoma duodenale & Necator americanus
  • Strongyloides stercoralis
• Intestinal worms


  • Roundworm
  • Whipworm
  • Pinworm
  • Seatworm
  • Society worm
  • Tiwa
  • Pudoc worm
  • Hookworms
  • Threadworm
• Habitat


  • Small Intestine
  • Large Intestine
  • Soil (free-living state) or man (parasitic state)
• Definitive Host/Final Host


  • Man
  • Man, other vertebrae
• Diagnostic Stage


  • Ova, adult
  • Egg
  • Ova
  • Larva or ova found in stool
  • Larva or ova found in stool
  • Rhabditiform larva
• Infective Stage


  • Ova (embryonated egg)
  • Fully embryonated egg
  • Ova
  • Larva found in fishes
  • 3rd stage larva (filariform)
  • Filariform larva
• Mode of Transmission


  • Ingestion
  • Ingestion
  • Ingestion, inhalation etc.
  • Ingestion of raw fish with the larva
  • Skin penetration of infective larva
  • Skin penetration of infective larva, autoinfection, and hyperinfection
• Nocturnal pruritus ani
• Loss of appetite
• Extraintestinal enterobiasis
• Capillaria philippinensis was discovered by Nelia Salazar at Pudoc, Ilocos Sur in 1963
• Some books mention that the C. philippinensis is a close relative of T. trichiura
• Natural Hosts


  • Migratory birds (herons, egrets, bitterns)
• Intermediate Hosts


  • Freshwater fishes, brackish water fishes, glass fishes
  • Bagtu
  • Bagsang
  • Birot
  • Ipon (Hypselotris bipartita)
• Adult Worm


  • Delicate tiny worms
  • Male: With chitinized spicules
  • Female: Usually with eggs in utero
• Eggs/Ova


  • Guitar, peanut-shaped
  • Striated cell
  • Flattened mucoid bipolar plugs
  • Morphologically similar with T. trichiura