General Characteristics and Epidemiology
Basic features of Enterobius
- Pointed tail
- Females: 8–13 mm long
- Males: 2–5 mm long
- Flattened on 1 side
Clinically relevant species
Enterobius vermicularis, or pinworm, causes enterobiasis.
Enterobiasis is the most common helminth infection in the United States and Western Europe.
- United States: 5%–15% of the general population (approximately 40 million people)
- Worldwide: 60 million to 100 million infections annually
- Children > adults
- Men > women
Humans are the primary hosts of E. vermicularis.
- Contact with contaminated surfaces and fomites
Host risk factors
- Disabled persons
- Healthcare, school, and prison workers
The entire life cycle of E. vermicularis takes place in the human GI tract.
- Ingestion of eggs → hatch and release larvae in the small intestine
- Adult worms reside in the cecum, appendix, and ascending colon.
- Female worms migrate through the rectum (usually at night) → deposit eggs on perianal skin
- Inflammatory reaction to worms and eggs on skin → intense pruritus
- Autoinfection occurs by patients transferring the eggs to the mouth with contaminated hands after scratching the affected region.
- Environmental contamination may also occur via the consumption of contaminated foods or contact with surfaces that are contaminated with eggs.
- Enterobiasis is often asymptomatic.
- Most common presentation: perianal itching (pruritus ani)
- More severe at night
- Excoriation from scratching can lead to secondary bacterial infections.
- Rare symptoms indicative of a high worm burden:
- Abdominal pain
- Nausea and vomiting
- Rare extraintestinal manifestations:
- Cervical granuloma
- Peritoneal inflammation
Diagnosis and Management
- Visual inspection of mobile worms:
- Near the anus
- On clothing or bed linens
- Cellophane tape test (often called the “Scotch tape test”):
- Apply an adhesive tape–like material to the perianal region.
- Eggs will accumulate on the adhesive surface.
- Examination of the tape under the microscope may show ova or worms.
- Improved yield at night or first thing in the morning
- Anthelmintic medications:
- Pyrantel pamoate
- Family members and classmates of the patient should be treated (owing to the high transmission rate).
Measures to reduce reinfection and spread:
- All linens and clothing should be washed.
- Frequent handwashing and bathing
- Clip fingernails.
Comparison of Similar Helminths
|Organism||Enterobius vermicularis||Toxocara canis||Ascaris lumbricoides||Strongyloides stercoralis||Schistosoma mansoni|
|Transmission||Fecal–oral||Fecal–oral||Fecal–oral||Skin contact with contaminated soil||Skin contact with contaminated water|
- Proctitis: inflammation of the rectal mucosa that may be caused by inflammatory bowel disease, infectious organisms (e.g., Salmonella, Shigella), radiation, and ischemia: Symptoms include pain, tenesmus, itching, and bleeding. Diagnosis depends on physical exam, proctoscopy or colonoscopy, cultures, and biopsy. Management depends on the etiology and can include antibiotics and steroids.
- Psoriasis: chronic inflammatory skin condition: Inverse psoriasis causes symmetric, smooth, shiny, and erythematous plaques in intertriginous areas, including the intergluteal region. Patients can experience pruritus, particularly at night. The diagnosis is clinical, and no eggs would be seen on a cellophane tape test. Management may include topical steroids, calcineurin inhibitors, vitamin D analogs, and emollients. Disease-modifying antirheumatic drugs and biologics may be used for severe cases.
- Atopic dermatitis: chronic inflammatory skin disease, usually due to a combination of genetics, immunologic dysfunction, and environmental factors: Patients will have pruritus and erythematous lesions on flexural surfaces, but it can occur, rarely, in the gluteal region. Diagnosis is based on history and exam, and the cellophane tape test will be negative for eggs. Management includes trigger avoidance, moisturizers, and topical steroids.
- Internal hemorrhoids: dilated vessels of the hemorrhoidal plexus in the anal canal, commonly caused by constipation: Internal hemorrhoids are painless, but pruritus can occur with prolapsed hemorrhoids. Visualization of hemorrhoids on exam will provide the diagnosis. Management includes stool softeners, topical hydrocortisone, and sitz baths. Additional treatment options are rubber band ligation and surgical removal.
- Perianal and perirectal abscess: collections of pus in the enclosed space near the perirectal tissues: These infections originate from obstruction of anal crypt glands. Patients present with severe pain in the anal or rectal area. Pruritus is less common. Finding a tender, fluctuant mass on physical exam can provide the diagnosis. Management requires prompt surgical incision and drainage, which may be followed by a course of antibiotics in some cases.
- Inflammatory bowel disease (IBD): includes Crohn’s disease and ulcerative colitis and is characterized by chronic inflammation of the GI tract due to a cell-mediated immune response to the GI mucosa: Symptoms include diarrhea, abdominal pain, weight loss, and extraintestinal manifestations. Diagnosis includes imaging, endoscopy, and biopsy. Treatment involves steroids, aminosalicylates, immunomodulatory, and biologic agents.
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