eMedicine Specialties > Infectious Diseases > Parasitic Infections

Pinworm

Sun Huh, MD, PhD, Chairman, Professor, Department of Parasitology, College of Medicine, Hallym University, Korea
Sooung Lee, PhD, Research Professor, Department of Environmental and Tropical Medicine, College of Medicine, Konkuk University, Korea

Updated: Aug 11, 2008

Introduction

Background

Pinworm, or Enterobius vermicularis, is prevalent throughout the temperate regions of the world and is the most common helminthic infection in the United States.

E vermicularis is a white slender nematode with a pointed tail. In humans, they reside in the caecum, appendix, and ascending colon (see Image 1). Female pinworms (8-13 mm long) are larger than their male counterparts (2-5 mm long). Pinworm infection is generally asymptomatic; however, some infected individuals experience sharp prickling pains or intense itching in the anal area, especially at night.

Pinworm infection is primarily a pediatric condition. Parents are typically infected via transmission through their children. 

Transmission can occur via direct contact with contaminated furniture, bedclothes, bedding, towels, toilets, doorknobs, or other objects. The parasite can also be transmitted during sexual contact.

Pathophysiology

Pinworms that inhabit the caecum and adjacent areas typically cause no symptoms. Diarrhea due to inflammation of the bowel wall can occur during acute infection.

The primary symptoms of pinworm infection, which include pruritus or a prickling sensation in the perianal area, are produced when a gravid female pinworm migrates to the anal area and inserts her tail pin into the mucosa for ovideposition.

Although pinworms have been found in the region of the appendix during histologic studies of acute appendicitis, the relationship is most likely incidental.¹

Frequency

United States

Pinworm infection is most common in persons who live in crowded living conditions and in individuals who are institutionalized. The general prevalence of pinworm infection in some regions may be as high as 12%.

International

Pinworm infection is most common in cosmopolitan areas in cool and temperate regions. Egg carrier rates vary by country, from 0.1-98.4%.

Mortality/Morbidity

Pinworm infection does not cause severe morbidity unless ectopic infection occurs. This rare complication occurs in individuals with conditions that compromise the integrity of the bowel wall (eg, inflammatory bowel disease). Parasites migrate through the bowel wall and are found in extracolonic sites. Ectopic enterobiases have been described in various locations, including the vagina, salpinx, inguinal area, genital area, pelvic peritoneum, omentum, liver, salivary glands, male genital tract, and even the lungs. They have also been associated with acute appendicitis, eosinophilic colitis, and eosinophilic gastroenteritis.²

Race

Pinworm infection has no reported racial predilection.

Sex

Pinworm infection has no sexual predilection.

Age

• Of all age groups, school-aged children are most at risk for pinworm infections.
• In adults, pinworm infection is most common in parents aged 30-39 years, typically because of transmission from their children aged 5-9 years.

Clinical

History

• Itching or prickling pain in the anal area
• Intense anal itching (Although a hospital-based study of children aged 2-12 years found that perianal itching was not significantly more common in children who are infected than in children who are uninfected, persons who are Enterobius egg–positive typically visit a physician because of perianal itching.)
• Restless sleep or difficulty sleeping
• Rarely, abdominal discomfort or loss of appetite

Physical

• Adult female worms may be visible in the anal area with the naked eye.
• The worm's appearance is easily confused with bits of cotton thread.

Causes

• Living with a person who is egg-positive
• Eating before washing hands
• Poor personal or group hygiene

Differential Diagnoses

Crohn Disease
Hidradenitis Suppurativa
Proctitis and Anusitis
Ulcerative Colitis

Other Problems to Be Considered

Occult fecal leakage
Anorectal fissure, fistula, sinus tract
Atopic eczema
Seborrheic dermatitis
Lichen planus
Candida infection
Tinea cruris
Dietary causes (eg, tomatoes, citrus fruit, chili pepper)
Psychogenic causes
Idiopathic pruritus

Workup

Laboratory Studies

• Use a perianal cellophane swab or cellophane tape to detect eggs³ (see Image 2).
  • The adult female pinworm dies after ovideposition; therefore, egg detection is associated with 5-11% false-positive rate and a 70-95% false-negative rate.
  • One report found that a single cellophane-tape examination yielded a sensitivity of 50%, 3 examinations yielded a sensitivity of 90%, and 5 examinations yielded a sensitivity of 99%.
  • Repeated examinations 1-2 days later produce more accurate results.

Imaging Studies

• Imaging studies are not necessary for diagnosis of pinworm infection.

Other Tests

• Other tests are not necessary for diagnosis of pinworm infection.

Histologic Findings

Microscopic examination shows the elongated ovoid egg distinctly compressed laterally and flattened on one side. The egg measures 50-60 µm X 20-30 µm and contains larva.

Treatment

Medical Care

• Anthelmintics are active against E vermicularis.
• Reinfection with E vermicularis immediately after the completion of drug therapy is common. Additionally, young pinworms may be resistant to drugs.  
  • Pinworm eggs remain infective in the environment for 2 weeks after deposition.
  • Reinfection from other persons who test positive for eggs is common.
  • Tests for pinworms carry a high false-negative rate. Therefore, successful eradication requires at least 3 doses of medication, separated by 3 weeks. In institutionalized settings, 3 doses separated by 3 weeks have been necessary to achieve successful eradication.
• The recommended treatment regimen for pinworm infection is as follows:  
  • Simultaneously treat all family members and/or classmates who are infected.
  • Prescribe drugs at least 3 times at 3-week intervals.
  • Personal and group hygiene must be improved. Individuals must wash their hands before eating. Discourage children from activities such as finger-sucking.
• If large numbers of children attending the same school test positive for pinworm eggs, the result of treatment is best if all classmates and family members of the children who are infected are treated 3 times at 3-week intervals. If less than 30% of class members test positive for pinworm eggs, treating only the children who have positive test results reduces the positive rate for eggs in that class.

Medication

The goals of pharmacotherapy are to eradicate the infestation, to reduce morbidity, and to prevent complications.

Anthelmintics

Parasite biochemical pathways are sufficiently different from the human host to allow selective interference by chemotherapeutic agents in relatively small doses.

Mebendazole (Vermox)

Causes worm death by selectively and irreversibly blocking uptake of glucose and other nutrients in susceptible adult intestine where helminths dwell.

Dosing

Adult

100 mg PO once at least 3 times at 3-wk intervals

Pediatric

<2 years: Not established
>2 years: Administer as in adults

Interactions

Carbamazepine and phenytoin may decrease effects; cimetidine may increase levels

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Adjust dose in hepatic impairment; if worm appears repeatedly in anal area, reduce dose to 25 mg for 10 kg of body weight; family members in close contact with patient should be treated

Pyrantel pamoate (Pin-Rid, Pin-X)

Depolarizing neuromuscular blocking agent. Inhibits cholinesterases, resulting in spastic paralysis of the worm.

Dosing

Adult

10 mg/kg PO once at least 3 times at 3-wk intervals

Pediatric

<2 years: Not established
>2 years: Administer as in adults

Interactions

In ascariasis, pyrantel and piperazine are mutually antagonistic and should not be used concomitantly; theophylline serum levels may increase in pediatric patients following administration

Contraindications

Documented hypersensitivity; hepatic disease; first trimester of pregnancy

Precautions

Pregnancy

D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus

Precautions

Caution in liver impairment, anemia, and malnutrition

Albendazole (Albenza)

Decreases ATP production in worm causing energy depletion, immobilization, and, finally, death. To avoid inflammatory response in CNS, patient must also be started on anticonvulsants and high-dose glucocorticoids.

Dosing

Adult

400 mg single PO at least 3 times at 3-wk intervals

Pediatric

10-14 mg/kg PO

Interactions

Coadministration with carbamazepine may decrease efficacy; dexamethasone, cimetidine, and praziquantel may increase toxicity

Contraindications

Documented hypersensitivity; altered liver function; jaundice after therapy

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Reported teratogenic effect to rats and rabbits; discontinue use if LFTs increase significantly (resume when levels decrease to pretest values)

Follow-up

Further Outpatient Care

Patients with pinworm infection must undergo follow-up examination to evaluate for reinfection after chemotherapy is completed. Although the first single examination may be negative for Enterobius eggs, a follow-up perianal swab is necessary if perianal itching or prickling pain persists.

Deterrence/Prevention

• Personal and group hygiene must be improved.  
  • Individuals must wash their hands before eating.
  • At-risk individuals should bathe upon waking to help reduce the egg contamination.
  • Discourage children from activities such as sucking their fingers and scratching bare anal areas.
• Treatment is much more effective if the child's family and classmates are treated at the same time.
• Washing sheets, clothes, and towels in a washing machine using regular laundry soap can eliminate pinworm eggs. However, eggs become noninfective after 2 weeks. Therefore, an emphasis on washing and environmental cleaning does not significantly improve the effectiveness of therapy.

Complications

• Pinworm infection does not cause severe morbidity unless ectopic infection occurs. This rare complication occurs in individuals with conditions that compromise the integrity of the bowel wall (eg, inflammatory bowel disease). Parasites migrate through the bowel wall and are found in extracolonic sites. Ectopic enterobiases have been described in various locations, including the vagina, salpinx, inguinal area, genital area, pelvic peritoneum, omentum, liver, and even the lungs.
• Some case reports have suggested that severe pinworm infection may be associated with an increased risk of appendicitis.¹
• Scratching the itchy area may cause eczema or a bacterial infection around the rectum. In girls, pinworm infection can spread to the vagina and may cause a vaginal discharge.

Prognosis

• Eradicating pinworm in groups of institutionalized persons is difficult. Continuous follow-up examination is necessary.
• Therapy is much more effective if the child's family and classmates are treated at the same time.

Patient Education

• Focus on handwashing, especially before eating.
• Washing sheets, clothes, and towels in a washing machine using regular laundry soap can eliminate pinworm eggs. Eggs become noninfective after 2 weeks. Therefore, an emphasis on washing and environmental cleaning does not significantly improve the effectiveness of therapy.
• For excellent patient education resources, visit eMedicine's Parasites and Worms Center and Esophagus, Stomach, and Intestine Center. Also, see eMedicine's patient education articles, Pinworms and Anal Itching.

Miscellaneous

Medicolegal Pitfalls

Failure to properly diagnose enterobiasis is a pitfall. The tools used to diagnose enterobiasis are not very sensitive or specific. Perianal swabs can detect the female pinworm only when her life cycle is terminated (after egg production). Therefore, false-negative or false-positive results can be a medicolegal pitfall.

Multimedia

Media file 1: Pinworm. Adult female worms of Enterobius vermicularis collected from a 2-year-old girl in a Korean orphanage after treatment with pyrantel pamoate 10 mg/kg, November 24, 1975.

Media file 2: Pinworm. Microscopic view of Enterobius vermicularis eggs attached to cellophane tape after a perianal swab from a child in kindergarten in Seoul, Korea, February 1999. Egg size was 50-60 μm X 20-30 μm. The eggs are elongated and ovoid, distinctly compressed laterally, and flattened on one side.

References

1. Ramezani MA, Dehghani MR. Relationship between Enterobius vermicularis and the incidence of acute appendicitis. Southeast Asian J Trop Med Public Health. Jan 2007;38(1):20-3. [Medline].

2. Tsibouris P, Galeas T, Moussia M, et al. Two cases of eosinophilic gastroenteritis and malabsorption due to Enterobious vermicularis. Dig Dis Sci. Dec 2005;50(12):2389-92. [Medline].

3. Cho SY, Kang SY. Significance Of Scotch-tape Anal Swab Technique In Diagnosis Of Enterobius Vermicularis Infection. Kisaengchunghak Chapchi. Dec 1975;13(2):102-114. [Medline].

4. Burkhart CN, Burkhart CG. Assessment of frequency, transmission, and genitourinary complications of enterobiasis (pinworms). Int J Dermatol. Oct 2005;44(10):837-40. [Medline].

5. CDC. Parasitic disease information. Division of parasitic diseases. Pinworm Infection. Available at http://www.cdc.gov/NCIDOD/dpd/parasites/pinworm/factsht_pinworm.htm.

6. Chan OT, Lee EK, Hardman JM, et al. The cockroach as a host for Trichinella and Enterobius vermicularis: implications for public health. Hawaii Med J. Mar 2004;63(3):74-7. [Medline].

7. Cho SY, Kang SY, Kim SI, et al. Effect of anthelmintics on the early stage of Enterobius vermicularis. Kisaengchunghak Chapchi. Jun 1985;23(1):7-17. [Medline].

8. Gargano R, Di Legami R, Maresi E, et al. Chronic sialoadenitis caused by Enterobius vermicularis: case report. Acta Otorhinolaryngol Ital. Aug 2003;23(4):319-21. [Medline].

9. Hong ST, Cho SY, Seo BS, et al. Chemotherapeutic control of Enterobius vermicularis infection in orphanages. Kisaengchunghak Chapchi. Jun 1980;18(1):37-44. [Medline].

10. Isik B, Yilmaz M, Karadag N, et al. Appendiceal Enterobius vermicularis infestation in adults. Int Surg. Jul-Aug 2007;92(4):221-5. [Medline].

11. Kang S, Jeon HK, Eom KS, et al. Egg positive rate of Enterobius vermicularis among preschool children in Cheongju, Chungcheongbuk-do, Korea. Korean J Parasitol. Sep 2006;44(3):247-9. [Medline].

12. Park JH, Han ET, Kim WH, et al. A survey of Enterobius vermicularis infection among children on western and southern coastal islands of the Republic of Korea. Korean J Parasitol. Dec 2005;43(4):129-34. [Medline].

13. Ryue HS, Jung JW, Pai KS. An Epidemiological Study on Refractory Enterobiasis. Korean J Pediatr. Feb/2004;47(2):177-182.

14. Song HJ, Cho CH, Kim JS, et al. Prevalence and risk factors for enterobiasis among preschool children in a metropolitan city in Korea. Parasitol Res. Sep 2003;91(1):46-50. [Medline].

15. The Korean Society for Parasitology. Atlas of Medical Parasitology. Available at http://www.atlas.or.kr/.

16. Tornieporth NG, Disko R, Brandis A, et al. Ectopic enterobiasis: a case report and review. J Infect. Jan 1992;24(1):87-90. [Medline].

17. Welch NM. Recent insights into the childhood "social diseases"--gonorrhea, scabies, pediculosis, pinworms. Clin Pediatr (Phila). Apr 1978;17(4):318-22. [Medline].

18. Yang YS, Kim SW, Jung SH, et al. Chemotherapeutic trial to control enterobiasis in schoolchildren. Korean J Parasitol. Dec 1997;35(4):265-9. [Medline].

19. Yoon HJ, Choi YJ, Lee SU, et al. Enterobius vermicularis egg positive rate of pre-school children in Chunchon, Korea (1999). Korean J Parasitol. Dec 2000;38(4):279-81. [Medline].

20. Zahariou A, Karamouti M, Papaioannou P. Enterobius vermicularis in the male urinary tract: a case report. J Med Case Reports. Nov 14 2007;1:137. [Medline].

Keywords

pinworm, pinworm infection, Enterobius vermicularis, E vermicularis, seatworm infection, threadworm infection, enterobiasis, oxyuriasis, helminthic infection

Contributor Information and Disclosures

Author

Sun Huh, MD, PhD, Chairman, Professor, Department of Parasitology, College of Medicine, Hallym University, Korea
Disclosure: Nothing to disclose.

Coauthor(s)

Sooung Lee, PhD, Research Professor, Department of Environmental and Tropical Medicine, College of Medicine, Konkuk University, Korea
Disclosure: Nothing to disclose.

Medical Editor

Mary Nettleman, MD, MS, Chair, Department of Medicine, Michigan State University
Mary Nettleman, MD, MS is a member of the following medical societies: American College of Physicians, American Federation for Medical Research, American Society for Microbiology, Central Society for Clinical Research, Infectious Diseases Society of America, and Society of General Internal Medicine
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

Gordon L Woods, MD, Consulting Staff, Department of Internal Medicine, University Medical Center
Gordon L Woods, MD is a member of the following medical societies: Society of General Internal Medicine
Disclosure: Nothing to disclose.

CME Editor

Eleftherios Mylonakis, MD, Clinical and Research Fellow, Department of Internal Medicine, Division of Infectious Diseases, Massachusetts General Hospital
Eleftherios Mylonakis, MD is a member of the following medical societies: American Association for the Advancement of Science, American College of Physicians, American Society for Microbiology, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

Chief Editor

Burke A Cunha, MD, Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital
Burke A Cunha, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

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