Enterobiasis (Pinworm)

A common intestinal helminth infection caused by the nematode Enterobius vermicularis. The parasite inhabits the cecum, appendix, and colon

Aetiology

Causative Organisms

Enterobius vermicularis

Morphology

Feature
Description
Adult worm
Small, white, thread-like
Female worm
8–13 mm long
Male worm
2–5 mm long
Habitat
Cecum and colon
Egg shape
Oval, flattened on one side
notion image
notion image
Eggs are planoconvex (D-shaped) and become infective within a few hours after deposition.

Pathophysiology

The infection occurs via the fecal–oral route.

Life Cycle Stages

  1. Ingestion of infective eggs
  1. Eggs hatch in the small intestine
  1. Larvae migrate to the cecum and colon
  1. Worms mature into adults
  1. Gravid female worms migrate to perianal region at night
  1. Eggs deposited on perianal skin
Eggs become infective within 4–6 hours.
notion image

Modes of Transmission

Mode
Explanation
Direct fecal–oral transmission
Hand-to-mouth spread
Autoinfection
Scratching transfers eggs to mouth
Fomite transmission
Contaminated clothing or bedding
Retroinfection
Larvae hatch and re-enter anus

Clinical Presentation

Classic Symptom

Symptom
Description
Nocturnal perianal pruritus
Most characteristic symptom
The itching is usually worse at night when female worms migrate.

Other Symptoms

Symptom
Mechanism
Sleep disturbance
Night itching
Irritability
Sleep disruption
Restlessness
Persistent discomfort
Abdominal pain
Mild intestinal irritation
Nausea
Intestinal involvement

Complications

Complication
Mechanism
Secondary bacterial infection
Excessive scratching
Vulvovaginitis
Worm migration to genital tract
Urinary tract irritation
Perineal invasion
Appendicitis (rare)
Worms in appendix

Investigations

Perianal Tape Test (Gold Standard)

Also called Graham-Scotch tape test.
Procedure
  1. Adhesive tape applied to perianal skin in the early morning
  1. Tape examined under microscope
Findings
Finding
  • Pinworm eggs
  • Egg characteristics:
Feature
Description
Shape
Oval
Symmetry
Flattened on one side
Shell
Thin

Stool Examination

Generally not useful, because eggs are usually deposited outside the intestine.

Direct Visualization

Adult worms may sometimes be seen:
  • Around the anus
  • In stool
  • On underwear or bedding
 

Management

First-Line Anthelmintic Drugs

Drug
Dose
Albendazole
400 mg SD
Mebendazole
100 mg SD
Pyrantel pamoate
10 mg/kg SD
 
Important principle:
  • Repeat dose after 2 weeks to eliminate newly hatched worms.
 
Note: Trichuris is less responsive to single-dose therapy, therefore multi-day regimens are preferred.