eMedicine Specialties > Pediatrics: General Medicine > Parasitology

Enterobiasis

Wayne Wolfram, MD, MPH,
Jennifer L Curry, DO, Resident Physician, Department of Emergency Medicine, St Vincent Mercy Medical Center

Updated: Nov 9, 2009

Introduction

Background

Enterobius vermicularis, a small nematode, is a common cause of helminthic infestation in the United States. The female nematode averages 10 mm X 0.7 mm, whereas males are smaller. All socioeconomic levels are affected. Infestation often occurs in family clusters. Infestation does not equate with poor home sanitary measures (an important point when discussing therapy).

Pathophysiology

E vermicularis is an obligate parasite; humans are the only natural host. Fecal-oral contamination via fomites (toys, clothes) is a common method of infestation. After ingestion, eggs usually hatch in the duodenum within 6 hours. Worms mature in as little as 2 weeks and have a life span of approximately 2 months.

Adult worms normally inhabit the terminal ileum, cecum, vermiform appendix, and proximal ascending colon. The worms live free in the intestinal lumen, and little evidence supports invasion of healthy tissue under normal conditions. The female worm migrates to the rectum after copulation and, if not expelled during defecation, migrates to the perineum (often at night), where an average of 11,000 eggs are released. Eggs become infectious within 6-8 hours and, under optimum conditions, remain infectious in the environment for as long as 3 weeks.

Because of the short incubation time until the ova are infectious, eggs that are deposited under the fingernails during scratching and then placed in the mouth may be a mode of reinfestation.

Frequency

United States

Prevalence is approximately 5-15% in the general population; however, this rate has declined in recent years. Prevalence rates are probably higher in institutionalized individuals. Humans are the only known host.

International

Prevalence data vary by country. E vermicularis infestation occurs worldwide.

Mortality/Morbidity

Secondary bacterial skin infection may develop from vigorous scratching to relieve pruritus. Reinfestation is common. Infection can develop as long as female pinworms continue to lay eggs on the skin. Restless sleeping may be due to pruritus ani. Infestation has been reported to cause enuresis.

Race

All races are subject to infestation.

Sex

Infestation can occur in males and females.

Age

The prevalence is greatest in children aged 5-9 years, but all ages can be affected.

Clinical

History

• Patients with enterobiasis are often asymptomatic. Worms may be incidentally discovered when they are seen in the perineal region.
• If patients are symptomatic, pruritus ani and pruritus vulvae are common presenting symptoms. However, one study failed to find an increase of these symptoms in infested children compared with matched control subjects.
• Restlessness during sleep is noted by the parents of many patients.
• Enuresis may be a symptom in children with pinworms.

Physical

• Patients often have excoriation or erythema of the perineum, vulvae, or both, but infestation can occur without these signs.
• Visual sighting of a worm by a reliable source (eg, a parent) is usually accepted as evidence of infestation and grounds for treatment.
• Worms can be found in stools or on the patient's perineum before bathing in the morning.
• Occasionally, the gravid female worm may aberrantly migrate into the female genitalia and produce vaginitis.¹ Incidental recovery at necropsy or surgery of small granulomatous lesions surrounding the worm, larvae, or eggs in the salpinx and peritoneum demonstrates the worm's ability to ascend the female genital tract.

Causes

• Enterobiasis is caused by the nematode E vermicularis.

Differential Diagnoses

Appendicitis
Ascariasis
Cervicitis
Contact Dermatitis
Giardiasis

Other Problems to Be Considered

Inflammatory bowel disease
Dermatitis secondary to poor hygiene
Dipylidium caninum (dog tapeworm) infection

Workup

Laboratory Studies

• Without a visual report, diagnosis of enterobiasis can be confirmed using the knowledge that eggs are normally deposited in great quantities on the perineum at night.
• Wide (2 inch) transparent tape is pressed against the perineum at night or in the morning before the patient bathes to capture eggs.² Three such specimens are usually consecutively collected.
• Diagnosis is made by identifying eggs under the low-power lens of microscope. Dilute sodium hydroxide or toluene should be added to the slide.

Imaging Studies

• Imaging studies are not indicated.

Treatment

Medical Care

• Fear, disgust, and guilt are common parental reactions to a parasitic worm infestation, such as enterobiasis. Many families present to the emergency department or their pediatrician with misconceptions about pinworms. In addition to prescribing medications, educating families about pinworms (see Patient Education) is helpful.
• Thorough and regular handwashing is effective in preventing disease transmission.

Medication

Mebendazole or albendazole are recommended as first-line treatment of pinworms. A second dose given 2 weeks after the initial dose helps prevent reoccurrences from reinfection.

Because asymptomatic infestation of other members in a household is frequent, simultaneously treating all household members may be reasonable. Families should be informed that repeat infestations are common. Reinfestation is treated with the same medications as the initial infestation.

Symptomatic relief of pruritus can be obtained by applying an antipruritic ointment or cream topically to the affected (usually perianal) region.

Anal albendazole may help with symptoms of pruritus ani. A recent letter to the editor stated a “local application of albendazole using an ear bud soaked with the residual albendazole suspension in the vial” in addition to the recommended oral dose of albendazole provided dramatic relief of pruritus ani.³

Ivermectin has been shown to have decreased efficacy as a single agent, compared with albendazole.⁴ However, it may possess efficacy when given as an adjunct.

Anthelmintics

Parasite biochemical pathways are different from the human host, thus toxicity is directed to the parasite, egg, or larvae. Mechanism of action varies within the drug class.

Pyrantel (Antiminth, Pin-Rid, Pin-X)

Depolarizing neuromuscular blocking agent and inhibits cholinesterases, resulting in spastic paralysis of the worm. Purging not necessary. May be taken with milk or fruit juices.

Dosing

Adult

11 mg/kg PO once; not to exceed 1 g; repeat treatment in 2 wk

Pediatric

Administer as in adults

Interactions

Theophylline serum levels may increase in pediatric patients, following pyrantel pamoate administration

Contraindications

Documented hypersensitivity; hepatic disease

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

Caution in liver impairment, anemia, or malnutrition

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; repeat treatment in 2 wk

Pediatric

Administer as in adults

Interactions

Carbamazepine and phenytoin may decrease effects of mebendazole; cimetidine may increase mebendazole 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

Albendazole (Albenza)

A benzimidazole carbamate drug that inhibits tubulin polymerization, resulting in degeneration of cytoplasmic microtubules. Decreases ATP production in worm, causing energy depletion, immobilization, and finally death. Converted in the liver to its primary metabolite, albendazole sulfoxide. Less than 1% of the primary metabolite is excreted in the urine. Plasma level is noted to rise significantly (as much as 5-fold) when ingested after high-fat meal. Experience with patients <6 y is limited.
To avoid inflammatory response in CNS, patient must also be started on anticonvulsants and high-dose glucocorticoids.

Dosing

Adult

400 mg PO as single dose; repeat in 2 wk if necessary

Pediatric

<2 years: 200 mg PO as single dose; repeat in 2 wk if necessary
>2 years: Administer as in adults

Interactions

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

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

Discontinue use if LFT results significantly increase (resume when levels decrease to pretest values); abdominal pain, nausea, vomiting, diarrhea, dizziness, vertigo, fever, increased intracranial pressure, and alopecia may occur

Follow-up

Inpatient & Outpatient Medications

• An antihelminthic medication should be prescribed to patients with enterobiasis .
• Application of an antipruritic ointment or albendazole may help control scratching.³

Deterrence/Prevention

• Thorough handwashing can deter transmission.

Complications

• Beware of skin infection from vigorous scratching to relieve pruritus.
• Pinworms have been associated with appendicitis.^5,6 However, small and large intestine ulcerations, perianal abscesses, intestinal pain, transient synovitis, or enuresis is believed to be coincidental and not causal.⁷
• If a patient with enterobiasis is refractory to treatment, consider the possibility of an infestation with Dipylidium caninum, which is a common tapeworm that infects domestic cats and dogs.⁸

Prognosis

• Prognosis is excellent, but reinfestation is common.

Patient Education

• Inform families that dogs and cats do not harbor E vermicularis.
• Inform families that infestation may occur in spite of proper child and household hygiene.
• Counsel families to avoid overreaction through aggressive sanitary measures. Because infectious eggs may be in bedclothes and dust and remain infectious for 20 days, wet-mopping floors or vacuuming carpets and washing bedclothes are prudent precautions.
• Reassuring families that pinworms are not a sexually transmitted disease and are not evidence of child abuse may be helpful.
• Keeping the patient's fingernails trimmed to prevent excoriations is helpful.
• Avoid scratching the area and nail biting because this is a cause of autoinfection.
• Encourage the patient to bathe in the morning, this significantly reduces the number of eggs.
• Children may return to school once they have received a dose of medication, bathed, and have nails trimmed.
• Bed linens should be washed in hot, soapy water.

Miscellaneous

Medicolegal Pitfalls

• Pinworms are rarely invasive. Attributing elevated serum immunoglobulin E (IgE) levels or eosinophilia to pinworms is unwise.

Multimedia

Media file 1: Because of the short incubation time until the ova are infectious, eggs that are deposited under the fingernails during scratching and then placed in the mouth may be a mode of reinfestation.

References

1. [Guideline] American College of Obstetricians and Gynecologists (ACOG). Vaginitis. Washington (DC): American College of Obstetricians and Gynecologists (ACOG); 2006 May. 12 p. (ACOG practice bulletin; no. 72). [Full Text].

2. Snow M. Pinning down pinworms. Nursing. May 2006;36(5):17. [Medline].

3. Singh SP, Panda C, Rout N, Mishra AP. Anal Albendazole application for pruritus ani in threadworm infestation. J Trop Pediatr. Dec 2005;51(6):386. [Medline].

4. Wen LY, Yan XL, Sun FH, Fang YY, Yang MJ, Lou LJ. A randomized, double-blind, multicenter clinical trial on the efficacy of ivermectin against intestinal nematode infections in China. Acta Trop. Jun 2008;106(3):190-4. [Medline].

5. 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].

6. Sodergren MH, Jethwa P, Wilkinson S, Kerwat R. Presenting features of Enterobius vermicularis in the vermiform appendix. Scand J Gastroenterol. 2009;44(4):457-61. [Medline].

7. Arca MJ, Gates RL, Groner JI, Hammond S, Caniano DA. Clinical manifestations of appendiceal pinworms in children: an institutional experience and a review of the literature. Pediatr Surg Int. May 2004;20(5):372-5. [Medline].

8. Samkari A, Kiska DL, Riddell SW, et al. Dipylidium caninum mimicking recurrent enterobius vermicularis (pinworm) infection. Clin Pediatr (Phila). May 2008;47(4):397-9. [Medline].

9. American Academy of Pediatrics. Pinworm Infection (Enterobius vermicularis). Report of the committee on infectious disease. 2009;519-20.

10. Hoekelman RA. Pinworm Infestation. In: Merck Manual of Diagnosis and Therapy. 15^th ed. 1987.

11. Kucik CJ, MartinGL, Sortor BV. Common Intestinal Parasites. Am Fam Physician. Mar 2004;69(5):11621-8.

12. Lormans JA, Wesel AJ, Vanprus OF. Mebendazole in enterobiasis. A clinical trial in mental retardates. Chemotherapy. 1975;21:255.

13. Otu-Bassey IB, Ejezie GC, Epoke J, Useh. Enterobiasis and its relationship with anal itching and enuresis among school-age children in Calabar, Nigeria. Ann Trop Med Parasitol. Sep 2005;99(6):611-6.

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. Symmers WS. Pathology of oxyuriasis; with special reference to granulomas due to the presence of Oxyuris vermicularis (Enterobius vermicularis) and its ova in the tissues. AMA Arch Pathol. Oct 1950;50(4):475-516. [Medline].

16. Weller TH, Sorenson CW. Enterobiasis: Its incidence and symptomatology in a group of 505 children. NEJM. 1941;224:143.

Keywords

enterobiasis, pinworms, oxyuriasis, human pinworm, pinworm infection, pruritus ani, pruritus vulvae, vaginitis, enuresis, treatment, diagnosis

Contributor Information and Disclosures

Author

Wayne Wolfram, MD, MPH, 
Wayne Wolfram, MD, MPH is a member of the following medical societies: American Academy of Emergency Medicine, American Academy of Pediatrics, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Coauthor(s)

Jennifer L Curry, DO, Resident Physician, Department of Emergency Medicine, St Vincent Mercy Medical Center
Jennifer L Curry, DO is a member of the following medical societies: American College of Emergency Physicians, American Osteopathic Association, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Medical Editor

Michael D Nissen, MBBS, BMedSc, FRACP, FRCPA, Associate Professor in Biomolecular, Biomedical Science & Health, Griffith University; Director of Infectious Diseases and Unit Head of Queensland Paediatric Infectious Laboratory, Sir Albert Sakzewski Viral Research Centre, Royal Children's Hospital
Michael D Nissen, MBBS, BMedSc, FRACP, FRCPA is a member of the following medical societies: American Academy of Pediatrics, American Society for Microbiology, Pediatric Infectious Diseases Society, Royal Australasian College of Physicians, and Royal College of Pathologists of Australasia
Disclosure: Nothing to disclose.

Pharmacy Editor

Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine
Disclosure: Pfizer Inc Stock Investment from financial planner; Avanir Pharma Stock Investment from financial planner ; WebMD Salary and stock Employment and investment from financial planner

Managing Editor

Martin Weisse, MD, Program Director, Associate Professor, Department of Pediatrics, West Virginia University
Martin Weisse, MD is a member of the following medical societies: Ambulatory Pediatric Association, American Academy of Pediatrics, and Pediatric Infectious Diseases Society
Disclosure: Nothing to disclose.

CME Editor

Robert W Tolan Jr, MD, Chief, Division of Allergy, Immunology and Infectious Diseases, The Children's Hospital at Saint Peter's University Hospital; Clinical Associate Professor of Pediatrics, Drexel University College of Medicine
Robert W Tolan Jr, MD is a member of the following medical societies: American Academy of Pediatrics, American Medical Association, American Society for Microbiology, American Society of Tropical Medicine and Hygiene, Infectious Diseases Society of America, Pediatric Infectious Diseases Society, Phi Beta Kappa, and Physicians for Social Responsibility
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Chief Editor

Russell W Steele, MD, Head, Division of Pediatric Infectious Diseases, Ochsner Children's Health Center; Clinical Professor, Department of Pediatrics, Tulane University School of Medicine
Russell W Steele, MD is a member of the following medical societies: American Academy of Pediatrics, American Association of Immunologists, American Pediatric Society, American Society for Microbiology, Infectious Diseases Society of America, Louisiana State Medical Society, Pediatric Infectious Diseases Society, Society for Pediatric Research, and Southern Medical Association
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