Intestinal Nematodes

• Roundworms


  Thread-like roundworms that live in a wide range of environments including soil and fresh and salt water
• Nema


  Means thread
• Roundworm structure


  • Elongated, cylindrical, unsegmented worms with tapering ends

  
• Roundworm species


  • Ascaris lumbricoides (Polymyrian)
  • Trichuris trichiura (Holymyarian)
  • Necator americanus (Meromyarian)
  • Ancylostoma duodenale (Meromyarian)
  • Strongyloides stercoralis
  • Enterobius vermicularis (Meromyarian)
  • Capillaria philippinensis

  
• Soil-transmitted helminth (STH)


  Disease of poverty
• Ascaris lumbricoides


  Most common and largest intestinal nematode, also known as "Giant roundworm"

  
• Ascaris lumbricoides occurs mostly in Tropics area (East Asia and Pacific Islands)
• Ascaris lumbricoides mostly infect 5-15 y/old
• Estimated Ascaris lumbricoides infection: 1 billion (70% in Asia)
• Mode of transmission (Ascaris lumbricoides)

  Fecal-oral route
• Infective stage (Ascaris lumbricoides)

  Fully Embryonated Egg

  
• Diagnostic stage (Ascaris lumbricoides)

  Adult Ascaris lumbricoides larvae

  
• Polymyrian type


  Having many cells in each quadrant of a cross section- used of the arrangement of muscle cells
• Adult Ascaris lumbricoides


  • Do not attached to the mucosa of the small intestines
  • Tape ends
  • Length: 15-35
  • Female are larger in size and have a genital girdle
  • Color: Whitish-pinkish
  • Development of egg laying adult worms: 9-11 weeks
  • Life span: 1 year

  
• Adult male Ascaris lumbricoides

  • Size: 10-31 cm
  • Ventrally curved posterior end with Spicules: 2
  • Have: Single, long, tortuous tubule
• Adult female Ascaris lumbricoides

  • Size: 22-35 cm. (larger compared to males)
  • With: smooth striated cuticles
  • Has: Paired reproductive organs in the posterior two-thirds
  • Produces about 200,000 eggs per day

  
• Ascaris lumbricoides larval/larvae morphology


  • Similar to adult

  
• Shapes of Ascaris lumbricoides ova

  • Fertilized Egg
  • Unfertilized Egg
  • Embryonated Egg

  
• Fertilized Ascaris lumbricoides egg

  • Golden brown in color
  • Broadly ovoid with thick and transparent shell, the innermost of which is called Vitelline layer

  
• Unfertilized Ascaris lumbricoides egg


  • 88 to 94 μm by 39 to 44 μm
  • Longer and narrower than fertile eggs
  • Larger than fertile egg
  • With a thin shell and irregular mammilated coating filled with refractile granules
  • Elongate with 2 layers of the eggshell – middle layer is thin with little or no outer albuminoid coat
  • Contains disorganized yolk cell appearing as tiny bubbles

  
• Decorticated fertilized Ascaris lumbricoides eggs

  • 45-75 μm x 35-50 μm
  • Broadly ovoid in shape
  • Eggshell (2 layers) is transparent due to absent albuminous coat
  • Contains a mass of organized yolk cells
• Fully embryonated Ascaris lumbricoides egg

  • Infective stage
  • Contains larvae
  • Eggshell is trilaminar and broadly ovoidal in shape
  • Brownish-yellow in color
  • Contains a coiled larva inside
  • Can survive in moist shaded soil

  
• Ascaris lumbricoides life cycle

  1. Eggs ingested, hatch in small intestine, larvae migrate to cecum/colon, penetrate intestinal wall, enter venules to liver, heart, pulmonary vessels, break out of capillaries to enter air sacs, molt in lungs, migrate to larynx/oropharynx, swallowed into digestive tract

  2. Development of egg-laying adult worms takes 9-11 weeks after egg ingestion

  3. Life span of adult worm is about 1 year

  4. Female produces 200,000 eggs per day, decreasing with increasing worm load

  5. Eggs deposited in soil when infected person defecates

  6. Eggs embryonate in 2-3 weeks in suitable soil conditions

  7. Larvae undergo 2 molts to reach 3rd stage within egg and become embryonated

  8. Embryonated eggs can survive in moist shaded soil for months to years

  
• Molting


  Casting off of an outer layer/covering
• Majority of Ascaris infections are asymptomatic
• Symptoms during Ascaris lumbricoides larval migration

  • Lung infiltration
  • Asthmatic attacks
  • Edema of the lips
  • Difficulty of breathing
  • Fever similar to pneumonia
• Symptoms of moderate Ascaris lumbricoides infection

  • Lactose intolerance
  • Vitamin A malabsorption
• Symptoms of heavy Ascaris lumbricoides infection

  • Bowel obstruction (due to bolus formation)
  • Intussusception
  • Volvulus that may result in bowel infarction and intestinal perforation
• 10 to 20 Ascaris worms may not show symptoms, but 100s of adults can produce intestinal obstruction

  
• Serious/fatal effects of Ascaris lumbricoides infection


  • Erratic migration of adult worms to biliary tract, appendix, pancreatic duct, peritoneal cavity

  
• Clinical diagnosis of ascariasis

  Inaccurate, as signs and symptoms are similar to other parasites
• Confirmatory diagnostic techniques for Ascaris lumbricoides

  • Direct fecal smear (DFS)
  • Kato thick Smear
  • Kato-Katz (single and double Kato-katz stool)
  • Sodium acetate-acetic acid-formalin (SAF)
  • Formalin ether/ethyl acetate concentration technique (FECT)
• Kato-Katz technique


  • For mass screening in school or community
  • Provides quantitative diagnosis in terms of the intensity of helminth infection in eggs per gram (epg) of stool
  • Useful in monitoring the efficacy of treatment
  • Sensitivity of 98%
• Sodium acetate-acetic acid-formalin (SAF) technique


  • Sensitivity of 93%
• Formalin ether/ethyl acetate concentration technique (FECT)


  • Higher sensitivity and detection rate for intestinal parasite infections
• Treatments for Ascaris lumbricoides

  • Albendazole (400 mg single dose, 200 mg for children 12-23 months)
  • Mebendazole (500 mg single dose)
  • Pyrantel pamoate (10 mg/kg, max. 1 g, single oral dose)
  • Ivermectin (200 μg/kg single dose)
  • Nitazoxanide (500 mg twice a day for 3 days, 100 mg twice a day for 3 days for children 1-3 years, 200 mg twice a day for 3 days for children 4-11 years)
• Benzimidazoles


  Bind to the parasites' b-tubulin resulting in the disruption of parasite microtubule polymerization, leading to the death of adult worms over several days
• Prevention of Ascaris lumbricoides infection

  • Avoid contact with soil contaminated with human feces
  • Do not grow food in night soil
  • Improve hygiene and sanitation practices
  • Proper food preparation
  • Regular deworming
• Infected stage (Trichuris trichiura)

  Embryonated Egg

  
• Diagnostic stage (Trichuris trichiura)

  Unembryonated Egg