Enterobius/Enterobiasis

Enterobiasis is a helminth infection caused by Enterobius vermicularis, also known as a pinworm. This infection is typically seen in children and is transmitted through the fecal–oral route. The primary clinical feature is anal pruritus, but patients are often asymptomatic. Visualization of ova or worms on cellophane tape testing is often required for diagnosis. Anthelmintic medications are used for treatment. Prevention of reinfection and transmission requires frequent handwashing and bathing, as well as washing of clothes and linens.

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General Characteristics and Epidemiology

Basic features of Enterobius

  • Nematode 
  • Appearance:
    • White 
    • Slender 
    • Pointed tail
  • Size: 
    • Females: 8–13 mm long
    • Males: 2–5 mm long
  • Eggs:
    • Elongated
    • Flattened on 1 side
    • Translucent

Clinically relevant species

Enterobius vermicularis, or pinworm, causes enterobiasis.

Epidemiology

Enterobiasis is the most common helminth infection in the United States and Western Europe.

  • Prevalence: 
    • United States: 5%–15% of the general population (approximately 40 million people)
    • Worldwide: 60 million to 100 million infections annually
  • Children > adults
  • Men > women

Pathogenesis

Reservoir

Humans are the primary hosts of E. vermicularis.

Transmission

  • Fecal–oral
  • Contact with contaminated surfaces and fomites

Host risk factors

  • Disabled persons
  • Schoolchildren
  • Prisoners
  • Healthcare, school, and prison workers

Life cycle

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.

Clinical Presentation

  • 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:
    • Vulvovaginitis
    • Salpingitis
    • Oophoritis
    • Cervical granuloma
    • Peritoneal inflammation

Diagnosis and Management

Diagnosis

  • 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
Photomicrograph Enterobius vermicularis eggs Enterobiasis

Photomicrograph of 8 Enterobius vermicularis eggs on cellophane tape

Image: Photomicrograph depicts eight eggs of the human pinworm, Enterobius vermicularis” by CDC. License: Public Domain

Management

Medical therapy:

  • Anthelmintic medications: 
    • Mebendazole
    • Pyrantel pamoate
    • Albendazole
  • 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

Table: Comparison of similar helminths and their associated diseases
OrganismEnterobius vermicularisToxocara canisAscaris lumbricoidesStrongyloides stercoralisSchistosoma mansoni
CharacteristicsNematodeNematodeNematodeNematodeTrematode
ReservoirHumansDogsHumans
  • Humans
  • Dogs
  • Cats
Humans
TransmissionFecal–oralFecal–oralFecal–oralSkin contact with contaminated soilSkin contact with contaminated water
Clinical
  • Pruritus ani
  • Abdominal pain and vomiting are less common.
  • Visceral larva migrans
  • Ocular larva migrans
  • Cough
  • Wheezing
  • Hemoptysis
  • Abdominal cramping
  • Nausea
  • Malnutrition
  • Cough
  • Wheezing
  • Abdominal pain
  • Diarrhea
  • Rash
  • Swimmer’s itch
  • Katayama fever
  • Chronic infections lead to granuloma formation causing brain, lung, intestinal, and liver disease.
Diagnosis
  • Clinical
  • Cellophane tape test
  • Serology
  • Biopsy
Stool analysis
  • Stool analysis
  • Serology
  • Stool analysis
  • Serology
Management
  • Albendazole
  • Mebendazole
  • Pyrantel pamoate
  • Albendazole
  • Mebendazole
  • Albendazole
  • Mebendazole
  • Ivermectin
  • Albendazole
Praziquantel
PreventionGood hygiene
  • Good hygiene
  • Deworm dogs.
  • Proper disposal of dog feces
  • Good hygiene
  • Clean raw fruits and vegetables before consuming.
  • Wear shoes and protective clothing.
  • Improve sanitation.
  • Avoid swimming or bathing in contaminated water.
  • Drink boiled or bottled water.
  • Improve sanitation.

Differential Diagnosis

  • 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.

References

  1. Ramezani MA, Dehghani MR. (1997). Relationship between Enterobius vermicularis and the incidence of acute appendicitis. Southeast Asian J Trop Med Public Health. https://reference.medscape.com/medline/abstract/17539241
  2. Cho SY, Kang SY. (1975). Significance of scotch-tape anal swab technique in the diagnosis of Enterobius vermicularis infection. Korean J Parasitol. https://www.parasitol.kr/journal/view.php?doi=10.3347/kjp.1975.13.2.102
  3. Bøås H, Tapia G, Sødahl JA, Rasmussen T, Rønningen KS. (2012). Enterobius vermicularis and risk factors in healthy Norwegian children. Pediatr Infect Dis J. https://reference.medscape.com/medline/abstract/22531241
  4. Centers for Disease Control and prevention. Parasitic Diseases Information. Retrieved April 13, 2021, from https://www.cdc.gov/parasites/pinworm/index.html
  5. Rawla P, Sharma S. (2020). Enterobius vermicularis. [online] StatPearls. Retrieved April 13, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK536974/
  6. Pearson RD. (2020). Pinworm infestation. MSD Manual Professional Version. Retrieved April 13, 2021, from https://www.msdmanuals.com/professional/infectious-diseases/nematodes-roundworms/pinworm-infestation
  7. Wolfram W, Afuwape LO, Indra S. (2016). Enterobiasis. In Steele, R.W. (Ed.), Medscape. Retrieved April 13, 2021, from https://emedicine.medscape.com/article/997814-overview
  8. Leder K, Weller PF. (2020). Enterobiasis (pinworm) and trichuriasis (whipworm). In Baron, E.L. (Ed.), UpToDate. Retrieved April 13, 2021, from https://www.uptodate.com/contents/enterobiasis-pinworm-and-trichuriasis-whipworm

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