Pinworm Infection

Life Cycle of the Parasite and Local Allergic Mechanisms

Causative Organism and Life Cycle

• The parasite: The pinworm Enterobius vermicularis (family Oxyuridae) is a small, off-white worm about 2–13 mm long.
• Fecal-oral transmission cycle:
  • Swallowing the eggs: Eggs containing larvae enter through the mouth via dirty hands, food or drink, or by inhaling airborne dust that carries eggs.
  • Hatching in the small intestine: The eggs hatch in the upper small intestine, and the larvae move down to the colon, maturing into adult worms within 2–6 weeks.
  • Migrating out to lay eggs: At night, when the anal sphincter relaxes, gravid female worms travel down the rectum and out through the anus to lay eggs in the skin folds around it. A single female can lay 10,000–15,000 eggs before dying.
  • Rapid development of infective larvae: At body temperature, the eggs become infective remarkably fast, in only 4–6 hours.

Why the Anal Area Itches and How Secondary Skin Problems Develop

• Irritating secretions: The female worm produces a sticky mucus to glue her eggs to the perianal skin. This mucus contains extracellular proteins that irritate the skin chemically and provoke a local hypersensitivity reaction.
• Allergic response: The hypersensitivity reaction releases histamine from mast cells, causing intense itching, typically between 10 p.m. and 2 a.m.
• Scratching and autoinfection: The itch leads to constant scratching, which breaks the skin and lodges eggs under the fingernails. They are then carried back to the mouth (direct reinfection) or spread to bedding, pillows and toys.

Clinical Features and Skin / Gynecologic Complications

Typical General Symptoms:

• Nighttime anal itching: The hallmark symptom. It causes restlessness, crying, light, broken sleep, and bedwetting or nighttime urination in children.
• Mild digestive upset: Mild pain around the navel or in the lower right abdomen, poor appetite, nausea and loose stools from irritation of the colon lining.

Signs on the Perianal Skin and Mucosa:

• Redness and swollen bumps around the anus: The perianal skin is congested and mildly inflamed, with linear scratch marks.
• Secondary eczematization: Long-term scratching thickens the skin and leads to lichenification, scaling and oozing around the anus and perineum.
• Secondary skin infection: Superinfection with Staphylococcus aureus or streptococci causes pustules and dirty yellow crusts.

Gynecologic and Nearby Complications (in Females):

• Vulvovaginitis: Female worms can stray from the anus across the perineum into the vagina, carrying gut bacteria with them and causing abnormal discharge and genital itching in girls.
• Rarely, cystitis or salpingitis from worms migrating upward.

Differential Diagnosis of Perianal Itching

Diagnostic Process at Haute-Derma

Clinical Examination and Family History:

• Assessing nighttime itching and looking with the naked eye for small white worms moving around the anus or on the surface of the stool.
• Asking whether other children in the family or classmates have similar symptoms.

Graham Cellophane Tape Test – the Gold Standard:

• How it is done: Clear tape is pressed lightly onto the skin folds around the anus first thing in the morning, right after waking and before using the toilet or bathing.
• The tape is stuck onto a glass slide and examined under the microscope at 10× and 40×.
• Typical appearance: Pinworm eggs are oval and flattened on one side, with a smooth, transparent shell; the larva inside is often clearly visible.
• Sensitivity: About 50% with a single test, rising to over 90% when done on 3 consecutive mornings.

Stool examination for eggs: Not recommended on its own, because pinworms rarely lay eggs inside the bowel. Eggs are found in stool in fewer than 10–15% of cases.

Whole-Family Treatment and Environmental Control at Haute-Derma

Treatment Principles

• Treat everyone at once: Everyone who lives in the same household or group must be treated at the same time, including people without symptoms.
• Repeat the dose: A second dose must be taken 2–3 weeks later. Current deworming drugs kill adult worms and larvae but not eggs, so the second dose wipes out worms that have hatched since, before they can mature and lay a new batch of eggs.

Oral Antiparasitic Medications

• Benzimidazoles (mebendazole / albendazole):
  • How they work: they block the worm's uptake of glucose, depleting its energy and killing it.
  • How to take: a single dose, followed by the same dose again 2–3 weeks later (required).
• Pyrantel pamoate:
  • How it works: it blocks the worm's neuromuscular transmission, causing spastic paralysis so the worms are expelled in the stool.
  • A safe option for young children and for pregnant women (only when a doctor considers treatment necessary). This dose also needs to be repeated after 2–3 weeks.

Treating Skin Symptoms and Secondary Infection

• Local itch relief: A soothing cream with zinc oxide, or a short course (3–5 days) of low-strength hydrocortisone, to calm the hypersensitivity reaction.
• Oral antihistamines: A second-generation antihistamine taken in the evening helps reduce itching and improve sleep.
• Treating secondary infection: A topical antibiotic cream if scratching has led to pustules or infected crusts.

Household Hygiene Measures

• On the first day of treatment, wash all bedding, pillows, mattress covers and underwear in water hotter than 60°C, then tumble-dry or dry in strong sunlight.
• Vacuum bedrooms, rugs and sofas thoroughly and clean children's toys.
• Keep everyone's fingernails short, and wash hands with soap before eating and after using the toilet.
• Don't shake out or beat bedding in the bedroom, as this releases eggs into the air.