Intestinal Nematodes

• Nematodes


  Also known as roundworms, elongated and cylindrical or filariform in shape, have bilateral symmetry, size of adults vary from a few millimeters to a meter long
• Nematodes


  • Have complex digestive systems
  • Body is covered by a cuticle
  • Middle layer is hypodermis
  • Inner layer is muscle
  • Have a pseudocoele which is a fluid-filled body cavity
  • Head has a buccal capsule with teeth or cutting plates
  • Have separate sexes (dioecious)
  • Some are parthenogenetic
• Males


  Usually curve-shaped with copulatory spicules, some have a copulatory bursa, reproductive system consists of testis, vas deferens, seminal vesicle, ejaculatory duct
• Females


  Larger than males, oviparous (lay eggs that develop outside the body), ovoviviparous (lay eggs that hatch inside the body), viviparous (gives birth to larvae), parthenogenetic (development of a female sex cell without fertilization)
• Nematodes


  • Have amphids and phasmids (sensory organs) - anterior/cephalic and posterior/caudal
  • Phasmids are used to group roundworms - phasmids vs aphasmids
• Aphasmids (of medical importance)

  • Trichuris
  • Trichinella
  • Capillaria
• Phasmids (of medical importance)

  • Strongyloides
  • Hookworm
  • Ascaris
  • Filarial Worms
  • Enterobius
• Medically important Nematodes grouped by habitat (adult worms)


  • Intestinal
  • Extraintestinal
• Medically important Nematodes grouped by mode of transmission

  • Ingestion of embryonated eggs
  • Skin penetration by filariform larvae
  • Mosquito bites
  • Ingestion of infective larvae
  • Autoinfection
• Intestinal Nematodes


  • Capillaria philippinensis
  • Ascaris lumbricoides
  • Strongyloides stercoralis
  • Enterobius vermicularis
  • Ancylostoma duodenale
  • Necator americanus
  • Trichuris trichiura
• Extraintestinal Nematodes


  • Trichinella spiralis
  • Wuchereria bancrofti
  • Brugia
  • Loa loa
  • Onchocerca volvulus
  • Mansonella spp.
  • Dracunclulus medinensis
  • Dirofilaria immitis
  • Angiostrongylus cantonensis
  • Anisakis
• Intestinal Nematodes by location

  • Small Intestine: Capillaria philippinensis, Ascaris lumbricoides, Strongyloides stercoralis, Hookworm, Trichinella spiralis
  • Large Intestine: Trichuris trichiura, Enterobius vermicularis
• Soil-transmitted Helminths


  • Capillaria philippinensis
  • Hookworms
  • Ascaris lumbricoides
  • Trichuris trichiura
  • Strongyloides stercoralis
• Nematodes with larval migration (heart-lungs)

  • Ascaris lumbricoides
  • Strongyloides stercoralis
  • Hookworms
• Infective stage of intestinal nematodes

  • Embryonated egg (except Strongyloides stercoralis, Capillaria philippinensis, Hookworms)
• Morphologic Forms


  • Eggs
  • Larvae
  • Adult worms
• Fertilization


  Fusion of male and female gametes, egg can be unfertilized
• Embryonation


  Development of fertilized ova in the environment, egg can be unembryonated
• Larvae (Juvenile Stage)


  Located inside the fertilized egg, undergoes maturation after emerging from the egg
• Ascaris lumbricoides


  Also known as giant intestinal roundworm, largest intestinal nematode, most common helminth in man (Philippines), soil plays a major role in development and transmission, infections are diseases of poverty
• Ascariasis


  Acquired through fecal-oral transmission of infective eggs in contaminated food or water, body site is intestine and larvae in lungs, diagnostic specimen is stool
• Adult Ascaris lumbricoides


  • Large and cylindrical, have smooth, striated cuticles, have a terminal mouth with three lips, have sensory papillae, reside in the small intestines, produce pepsin inhibitor 3 (PI3) and phosphorylcholine
• Adult Male Ascaris lumbricoides

  Measure 10-31 cm, have a ventrally curved posterior end with two spicules
• Adult Female Ascaris lumbricoides

  Measure 22-35 cm, have paired reproductive organs in the posterior two-thirds
• Unfertilized/Infertile Ascaris lumbricoides Eggs

  • Measure 88 to 94 μm by 39 to 44 μm, longer and narrower, have a thinner shell and irregular mammilated coating, filled with refractile granules, inner layer is glycogen with lecithin granules, outer layer is albuminoid mammillation
• Fertile Ascaris lumbricoides Eggs

  • Measure 70 μm by 35 to 50 μm, have an outer coarsely mammillated albuminous covering, supporting structures include a thick, transparent, hyaline shell (glycogen membrane) with a thick outer layer, and a delicate vitelline, lipoidal, inner membrane
• Ascaris lumbricoides Life Cycle

  1. Ingestion of embryonated eggs

  2. Eggs hatch in the lumen of small intestine, release larvae

  3. Larval migration (liver to lungs)

  4. Larvae migrate to cecum or proximal colon, venules, liver, portal vein, heart and pulmonary vessels, air sacs of lungs, undergo molting - L2 to L4

  5. Larval migration (lungs to digestive tract), lungs (molting) to larynx and oropharynx, swallowed in the digestive tract

  6. Maturation occurs in the small intestine, lifespan is approx. 1 year, adult female can produce about 200,000 eggs/day, deposited in the soil when a person with Ascaris defecates

  7. Embryonation occurs in the soil, takes 2 to 3 weeks for eggs to develop into the infective stage, occurs at favorable conditions - suitable temperature, moist, humid, shaded soil
• Ingestion of Embryonated Eggs

  INFECTIVE STAGE
• Larval Migration (liver to lungs)


  DIAGNOSTIC STAGE
• Larval Migration (lungs to digestive tract)


  DIAGNOSTIC STAGE
• Maturation


  DIAGNOSTIC STAGE
• Eggs in feces


  DIAGNOSTIC STAGE
• Pathogenesis of Ascariasis


  • Can be caused by migrating larvae, induces an allergic reaction, adult worms cause nutritional and toxic effects
• Loeffler's Syndrome (Eosinophilic Pneumonitis)

  Caused by an allergic reaction to the migrating larvae, lung infiltration (ascaris pneumonia), blood-tinged sputum with Charcot-Leyden crystals, asthmatic attacks, difficulty in breathing, fever, eosinophilia
• Vitamin A deficiency


  Often accompanied by protein-energy malnutrition, occurs when worm burden is heavy
• Bowel Obstruction


  Caused by bolus formation, can result in intestinal perforation
• Ectopic Ascariasis (Wanderlust)


  Caused by the random probing and insinuating of worms, enhanced when the host's temperature is above 39 C, worm may penetrate openings of biliary duct, pancreatic duct, liver parenchyma, esophagus, trachea, appendix
• Diagnosis of Ascariasis is done through Direct Fecal Smear, Kato technique or Cellophane Thick smear method, Kato-Katz technique (Modified Kato technique) - quantitative
• Drugs used to treat Ascariasis

  • Albendazole (drug of choice)
  • Mebendazole
  • Pyrantel pamoate
  • Ivermectin
• Ascarids


  • Ascaris suum (ascaris of pigs)
  • Toxocara canis (ascaris of dogs, lance-shaped)
  • Toxocara cati (ascaris of cats, arrow-shaped)