NEMATODES 2

• Rhabditiform Larva


  1. Indistinguishable among hookworms

  2. Feeding larva

  3. Long buccal cavity, small genital primordium
• Pathology of Hookworm Infection

  1. Skin at the site of entry of the filariform larvae

  2. Lung during larval migration

  3. Small intestine as ha
• Adult hookworms

  • Necator americanus is smaller than Ancylostoma duodenale
  • Head of Necator americanus is curved opposite to the curvature of the body, while Ancylostoma duodenale's head is curved in the same direction as the body
  • Female hookworms are larger than males
  • Male hookworms have a posterior end equipped with an expansion with rib-like rays for copulation called caudal bursa
  • Ancylostoma duodenale has 2 pairs of curved ventral teeth, TRIDIGITATE dorsal ray, and 2 spicules; Necator americanus has a ventral pair of semilunar cutting plates, BIFID dorsal ray, and FUSED spicules
• Human hookworms

  • Necator americanus
  • Ancylostoma duodenale
• Ova


  • Difficult to distinguish the eggs of A. duodenale vs N. americanus
  • Oval-round with thin, smooth and colorless albuminous (transparent) eggshell
  • Contains clear space between the eggshell and ovum
  • Ovum usually contains 2-8 cells when passed with feces
  • Size of 57-76um x 35-47um
• Hookworms


  • Small, cylindrical, fusiform, grayish-white, blood-sucking nematodes
  • Attach to the mucosa of the small intestine
  • Arrangement of somatic musculature: meromyarian
• Filariform Larvae

  1. Non-feeding larva

  2. Infective stage

  3. Short esophagus, pointed tail for hookworms; Long esophagus, notched tail for Strongyloides stercoralis
• Pathology of Hookworm Infection

  1. Skin at the site of entry of the filariform larvae

  2. Lung during larval migration

  3. Small intestine as habitat of adult worm
• Diagnosis

  1. Recovery of eggs from feces

  2. DFS, Kato-Katz technique

  3. Concentration method

  4. Culture method like Harada-Mori

  5. Allow hatching of eggs to larvae

  6. Others: PCR, ELISA
• Skin


  • Ground itch or Dew itch
  • Related to contact with soil, especially on a dewy morning
  • Maculopapular lesions and localized erythema due to penetration of filariform larva
  • Lasting for 2 weeks
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• Treatment

  1. Drug of Choice: Albendazole 400 mg single dose

  2. Alternative: Mebendazole 500 mg single dose
• Other Pharmacologic Intervention

  1. Iron supplementation

  2. Adequate diet to address hypoalbuminemia
• Ovum


  • Contains clear space between the eggshell and ovum
  • Usually contains 2-8 cells when passed with feces
  • Size of 57-76um x 35-47um
• Prevention and Control

  1. WASHED Framework for the control of STH

  2. Provision of safe water

  3. Environmental sanitation

  4. Hygiene education

  5. Regular deworming

  6. On-going trial on vaccine against hookworm
• Lungs


  • Loeffler Syndrome
  • Bronchitis and pneumonitis due to the abundant larvae migrating through the lungs
  • Minute hemorrhages with eosinophilic and leukocytic infiltration
• Small Intestine

  • Buccal capsule attaches the worm to the intestinal wall, saliva contains anticoagulant which keeps the area bleeding
  • Microcytic, hypochromic anemia due to loss of iron
  • Hypoalbuminemia due to loss of albumin
  • Abdominal pain, diarrhea, steatorrhea, exertional dyspnea, weakness, dizziness
• War on Worms (WOW) - https://www.facebook.com/WarOnWormsPhilippines/
• Life Cycle of Strongyloides stercoralis

  1. Invasion of the skin by the filariform larvae

  2. Migration of larvae through the body

  3. Penetration of the intestinal mucosa by adult female worms
• Strongyloides stercoralis

  • Facultative parasite
  • Free-living form (rhabditiform)
  • Parasitic form (filariform female)
• Characteristics of Free-Living Male


  • Smaller than the female measuring 0.7mm x 0.04mm
  • Ventrally curved tail, two copulatory spicules, a gubernaculum, no caudal alae
• Characteristics of Rhabditiform Larva


  • Short buccal cavity, prominent genital primordium
• Migration of Larva

  • Lungs: Destroyed causing lobar pneumonia with hemorrhage, cough, and tracheal irritation
• Characteristics of Parasitic Female

  • Colorless, semi-transparent, with a finely striated cuticle, measuring 2.2mm x 0.04mm
  • Reproduction through Parthenogenesis
  • Short buccal cavity with 4 indistinct lips
  • Long, slender esophagus extending to the anterior fourth of the body
  • Intestine is continuous to the subterminal anus
  • Vulva at one-third the length of the body from the posterior end
  • Uteri contain a single file of 9-12 ova
• Skin


  • Larva currens
  • Erythematous serpiginous skin lesion at the side of entry caused by rapid moving filariform larva with pruritus and urticaria
• Characteristics of Ovum

  • Clear, thin shell similar to hookworms
• Strongyloides stercoralis


  Also known as Threadworm
• Characteristics of Free-Living Female

  • Reproduction: Oviparous
  • Smaller than parasitic female measuring 1mm x 0.06mm
  • Muscular double-bulbed esophagus
  • Intestine is a straight cylindrical tube
• Characteristics of Filariform Larvae

  • Hookworms: Short esophagus, pointed tail
  • Strongyloides stercoralis: Long esophagus, notched tail
• Pathogenesis and Clinical Manifestations

  1. Three Phases of Acute Infection: 1. Invasion of the skin by the filariform larvae

  2. Migration of larvae through the body

  3. Penetration of the intestinal mucosa by adult female worms
• Complications

  Edema, emaciation, anorexia, anemia, lobar pneumonia, ileus, intestinal obstruction, gastrointestinal bleeding, malabsorption
• Prevention and Control

  1. WASHED Framework for the control of STH

  2. Provision of safe water

  3. Environmental sanitation

  4. Hygiene education

  5. Regular deworming

  6. Ongoing trial on vaccine against hookworm
• Chronic Strongyloidiasis in Intestine

  1. Often asymptomatic

  2. May have intermittent vomiting, diarrhea, constipation, and borborygmi

  3. Anal pruritus, urticaria, larva currens

  4. Recurrent asthma, nephritic syndrome
• Treatment

  Anti-helminths: Albendazole, thiabendazole (contraindicated in pregnant women), Ivermectin (best for chronic uncomplicated strongyloidiasis)
• Infection in Intestine

  1. Due to penetration of intestinal mucosa by adult female worms

  2. Light infection may be asymptomatic

  3. Moderate infection: diarrhea alternating with constipation

  4. Heavy infection: intractable, painless, intermittent diarrhea characterized by episodes of watery and bloody stools (Cochin-China Diarrhea)

  5. Hyperinfection: syndrome of accelerated autoinfection usually among immunocompromised

  6. Exacerbation of GIT and RT symptoms

  7. Increased number of larvae in stool samples and even in sputum
• Diagnosis

  1. Clue: unexplained eosinophilia

  2. Culture method

  3. Harada-Mori culture

  4. Nutrient agar plate

  5. Concentration techniques

  6. Others: Duodenal aspiration, Beale’s string test, small bowel biopsy

  7. Sputum or urine microscopic examination (disseminated strongyloidiasis)
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• Life cycle of Enterobius vermicularis

  1. Gravid female migrates to perianal region during evening to deposit eggs

  2. Embryonated eggs fully mature within 4-6 hours and can lead to autoinfection

  3. Infection by ingestion of fully embryonated egg

  4. Embryonated egg containing 3rd stage larva attaches in the small intestine and then passes down to the large intestine
• Risk factors for Enterobius vermicularis infection

  • Overcrowding
  • Thumb-sucking
  • Nail-biting
  • Lack of parental knowledge on pinworms
• Commonly affected by Enterobius vermicularis


  • School-aged and pre-school-aged children
  • Institutionalized persons
  • Household members and caretakers of persons with enterbiasis