Enterobius

• Enterobius vermicularis

  Intestinal parasitic nematode

  
• Enterobius vermicularis

  • Dioecious: separate sexes (male and female)
  • Common name: Pinworn (because of the long pointed tail of the female resembling a pin), Seatworm
  • Host: Humans only
  • Habitat: large intestine – cecum

  
• Diseases caused by the parasite

  Enterobiasis or Oxyuriasis (oxyuris: sharp tail), Acute appendicitis
• This nematode is also belongs to the family oxyuridae
• Epidemiology

  • Has a worldwide distribution, occurring in both temperate and tropical regions
  • High prevalence in both developed and developing countries
  • Occurs in more than one person in the household or an institutional setting – affects people in groups
• Commonly Affected

  • School-aged and pre-school-aged children
  • Institutionalized persons
  • Household members and caretakers of persons with enterobiasis
• Risk Factors

  • Overcrowding
  • Thumb-sucking
  • Nail-biting
  • Lack of parental knowledge on pinworms
• Adult male

  • 2-5mm x 0.1-0.2mm with curved tail and a single spicule, resembling number "6"
  • Males are rarely seen because they usually die after copulation
• Adult female

  • 8-13mm x 0.1- 0.2mm with long pointed tail, fusiform body
• Anterior End (both male and female)

  • Cephalic Alae – tapered and flunked on each side by a wing-liked cuticular extensions of the head
  • The esophagus is slender, terminating in a prominent bulbous portion – posterior esophageal bulb
• Meromyarian

  Arrangement of Somatic Musculature

  
• Rhabditiform Larva

  • 140-150um x 10um
  • With characteristic esophageal bulb
  • No cephalic alae or cuticular expansion in the anterior end
• Ova

  • 50-60um x 20-30um (average 55um x 60um)
  • D-shaped: Asymmetrical with one side flatted and the side convex
  • Translucent shell (colorless and not stained with bile)
  • Outer triple albuminous covering: mechanical protection
  • Inner embryonic lipoidal membrane: chemical protection
  • Embryo: tadpole-like, matures outside the host within 4-6 hours – protected by the outer triple albuminous covering and inner embryonic lipoidal membrane
• Life Cycle

  1. Adult gravid female Enterobius vermicularis migrate from the colon to the anus to deposit already embryonated eggs on the perianal folds which usually happens in the evening hours

  2. The larva containing eggs in the perianal folds become fully matured within 4 to 6 hours. Infection occurs when these fully embryonated eggs will be ingested by the same host which is also known as autoinfection, it can also be ingested by other host usually close contacts – usually members of the household through contaminated clothing, beddings, and among others

  3. After ingestion, the embryonated egg which contains the third stage larva hatches in the small intestine, usually in the duodenum. The larva then passes down the remaining parts of the small intestine and ultimately reaches the habitat which is the large intestine, usually the cecum

  4. The adult male and female copulates and the male usually dies after copulation. The female then becomes gravid, eventually it will migrate down to the anus to deposit the embryonated eggs in the perianal folds and the female dies after oviposition – and the cycle continues

  
• Rarely, the eggs that are attached to the blanket or clothes may be airborne and can be inhaled or swallowed, this mode of transmission is called airborne transmission
• Also in some instances, the embryonated eggs in the perianal folds may hatch larvae, if this happens, the hatched larvae may migrate back to the large intestine and establish or mature there as adult parasites – this is called retroinfection, which is a special type of autoinfection

  
• Diagnostic stages

  • Embryonated egg
  • Adult (sometimes)
• Infective stage

  • Embryonated egg – containing third stage larva
• Modes of transmission

  • Ingestion
  • Inhalation
  • Autoinfection and retroinfection
• No larval heart-lung migration
• Pathogenesis and Clinical Manifestations

  • Relatively innocuous parasite
  • Rarely produce serious medical problem
• Pruritus ani


  Itchiness of the perianal area specially at night
• Constant scratching of the perianal area and the perinium may cause excoriation and possibly secondary bacterial infection
• Intense pruritus ani may result to insomnia and restlessness at night
• Vaginal irritation

  Adult female worm invading the vagina → irritation
• Acute appendicitis


  The adult Enterobius vermicularis may migrate to the appendix causing obstruction and inflammation of the appendix resulting to acute appendicitis
• Clinical diagnosis: Pruritus ani (patients with this symptom relieves in scratching)
• Pruritus ani is NOT specific to Enterobiasis
• Laboratory diagnosis

  • Microscopic examination: Identification of eggs
  • Detection of adult on anal skin or feces
  • Tissue biopsy
  • Graham Scotch Tape Method
• Treatment

  • Mebendazole 100mg
  • Albendazole 400mg (200mg in children under 2 years old)
  • Pyrantel pamoate 11mg/kg, maximum dose of 1g
• Radical Cure: Drug therapy or administration should be given again after 2 weeks to kill any worms that might have hatched from eggs present during initial treatment

  
• Familial parasitic disease: TREAT THE ENTIRE HOUSEHOLD – to prevent reintroduction of the parasite to the other members of the household
• Prevention and Control

  • ONLY INTESTINAL NEMATODE INFECTION that cannot be controlled through sanitary disposal of human feces
  • Personal hygiene: Fingernails should be cut short, Hand washing after using the toilet, and before and after meals
  • Infected person is suggested to use showers instead of bathtubs
  • Infected person should sleep alone until adequately treated
  • Underwear, night clothes, blankets, and bedsheet should be handled with care and washed in hot soapy water
  • Drug therapy of the entire household
• Life Cycle Summary

  1. Gravid adult female Enterobius vermicularis deposit eggs on perianal folds

  2. Infection occurs via self-inoculation (transferring eggs to the mouth with hands that have scratched the perianal area) or through exposure to eggs in the environment (e.g. contaminated surfaces, clothes, bed linens, etc.)

  3. Following ingestion of infective eggs, the larvae hatch in the small intestine and the adults establish themselves in the colon, usually in the cecum

  4. The time interval from ingestion of infective eggs to oviposition by the adult females is about one month

  5. Gravid females migrate nocturnally outside the anus and oviposit while crawling on the skin of the perianal area

  6. The larvae contained inside the eggs develop (the eggs become infective) in 4 to 6 hours under optimal conditions

  7. Rarely, eggs may become airborne and be inhaled and swallowed. Retroinfection, or the migration of newly hatched larvae from the anal skin back into the rectum, may occur but the frequency with which this happens is unknown