Enterobiasis or Pinworm Infection Case File

Enterobiasis or Pinworm Infection Case File

Eugene C.Toy, MD, Cynthia Debord, PHD, Audrey Wanger, PHD, Gilbert Castro, PHD, James D. Kettering, PHD, Donald Briscoe, MD

CASE 47

A 4-year-old girl is brought to the physician’s office by her mother because of anal itching. The mother has noticed her daughter scratching and rubbing her anal area frequently for the past few days. Her anal area has been getting red and raw from all the scratching. Mother has used some petrolatum and hydrocortisone cream, but it hasn’t helped much. The child has not had any obvious skin rashes and is not scratching any other part of her body. She has not had diarrhea. She takes no medications and has no significant medical history. She attends day care 4 days a week. On examination, she is a well-appearing child. Her vital signs and general examination are normal. Examination of her perianal area reveals some erythema and excoriation from scratching. You perform a microscopic examination of a sample collected by touching the perianal region with a piece of clear cellophane tape.

◆ What diagnostic finding are you likely to see on this microscopic examination?

◆ What is the organism responsible for this infection?

ANSWERS TO CASE 47: ENTEROBIASIS OR PINWORM INFECTION

Summary: A 4-year-old girl has perianal pruritus. The diagnosis is made by microscopic examination of a sample collected by touching the perianal region with a piece of clear cellophane tape.

◆ Diagnostic finding likely to see on this microscopic examination: Thin-walled, ovoid eggs that are flattened on one side and contain a nematode larva.

◆ Organism responsible for this infection: Enterobius vermicularis.

CLINICAL CORRELATION

Enterobius vermicularis, commonly called the pinworm, is the most common cause of helminthic infections in the United States and is endemic around the world. Humans are the only known host for E. vermicularis, but other vertebrates can be infected with different species of this nematode. Adult worms, approximately 1 cm in length, white and thread-like in appearance, inhabit the large intestine. Gravid females migrate to the perianal and perineal regions at night to lay eggs that are immediately infective. Infection is more common in children than adults and is often asymptomatic. However, a variety of symptoms are ascribed to pinworms. Atypically, worms are sometimes found in an inflamed appendix and there are rare reports of worms reaching the genital tract and producing vaginitis. By far the most common signs of infection occur in children and include restless sleep and tiredness during the day. However, more common symptoms consist of anal or perianal itching because of the adult worms crawling on the skin. The eggs can also cause local itching, which may be more intense in secondary infections as a result of allergic reactions to their antigenic coating. Frequent scratching results in transfer to the hands and areas under the fingernails. Eggs are frequently transferred to clothing, bedding, toys, and dust, where they can survive for several weeks. Through hand-to-mouth transmission, the eggs are ingested and hatch in the duodenum. Larvae released from eggs reside in the cecum and reach adult stage in about a month. Infections are acute, generally lasting 4–8 weeks. Considering the relatively short duration of a single infection, chronic enterobiasis is caused by reinfection.

APPROACH TO THE SUSPECTED Enterobius INFECTION

Objectives

1. Learn the life cycle of E. vermicularis and the epidemiology and clinical course of infection.

2. Be able to describe three basic aspects of infection: transmission, diagnosis, and treatment/prevention.

Definitions

Pinworm: Common name for Enterobius vermicularis.

Cervical alae: An extension of a lateral cuticular protuberance or lateral line on the body surface of the pinworm that extends to the head region and appears microscopically as a “flared” region or collar. Adult worms are identified, in part, by the presence of cervical alae which are prominent structures when examined microscopically.

Nocturnal migration: Refers to the tendency of pinworms to migrate at night from the colon, out the anus, to the perianal and perineal regions to deposit eggs.

Larvated egg: Refers to eggs that contain a larval stage and are deposited by pinworms on the skin.

DISCUSSION

Characteristics of Enterobiasis That Impact Transmission

A patient acquires infection by ingesting the pinworm eggs containing infective larvae. Ingested eggs hatch in the small intestine releasing larvae that migrate to the cecal area and mature into adult male and female worms that are free or insecurely attached to the mucosa. The period between ingestion of eggs to maturation takes approximately 3–4 weeks. Following copulation, the female pinworms produce eggs. Rather than release eggs in the bowel, the female worms migrate out the anus onto the surrounding skin and release eggs. Worm migration usually occurs at night. Each female will lay thousands of microscopic, larvated eggs. Pinworm eggs are infective within a few hours after being deposited on the skin. They can survive up to 2 weeks on clothing, bedding, or other objects. Individuals can become infected after accidentally swallowing infective pinworm eggs from contaminated surfaces or fingers. The duration of a single infection is 4–8 weeks.

Diagnosis

Although Enterobius is an intestinal parasite, eggs are rarely found during laboratory examinations of stools. If a person is suspected of having pinworms, the so-called “scotch tape test” should be used to identify the parasite. Transparent adhesive tape, sometime attached to the end of tongue depressor or “pinworm paddle,” is pressed in the anal region. This procedure involves the help of a patient or parents of suspected children. The tape is then transferred to a glass slide, sticky side down. The slide should then be examined microscopically for eggs. Pinworm eggs are approximately 20 × 50 μm characteristically flattened on one side and usually contain an active larva. Because bathing or having a bowel movement may remove eggs, the scotch tape impression should be made on awakening in the morning. In children, samples taken from under the fingernails may also contain eggs because scratching of the anal area is common.

A definitive diagnosis may also be made on recovery and identification of adult worms seen directly in bedclothes or around the anal area. The female pinworm has a sharply pointed tail and anterior alae that form a collar-like structure around the mouth. The female worm is about 1 cm long with a diameter approximately 0.5 mm. In female worms that are gravid, the uterus filled with easily identifiable eggs is a common feature.

Treatment and Prevention

Highly effective drugs in the treatment of enterobiasis are pyrantel pamoate and mebendazole, given as a single dose, with a repeat dose administered 2 weeks later. Mebendazole is a broad spectrum antinematode agent that has a high therapeutic index. Close family contacts of infected individuals should be treated as well. If reinfection occurs, the source of the infection should be identified. Therefore, playmates, schoolmates, close contacts outside the house, and household members should be considered. Each infected person should receive the two-dose treatment and, if necessary, more than two doses. In short, the importance of determining infection in the entire family or contacts should be explained in terms of the life cycle of the worm and personal, and group hygiene should be stressed.

Synopsis

The synopsis of enterobiasis is presented in Table 47-1.

Table 47-1

COMPREHENSION QUESTIONS

[47.1] In which of the following life cycle stages is enterobiasis transmitted?

A. Larva

B. Egg

C. Adult

D. Cyst

E. Oocyst

[47.2] Which of the following is the drug of choice in treating enterobiasis?

A. Mebendazole

B. Metronidazole

C. Piperazine

D. Praziquantel

E. Chloroquine

[47.3] A parent of a child suffering from disturbed sleep and restlessness calls the family physician and states that her child is once again infected with pinworms and asks if she can administer the same medicine that was used to cure an earlier infection. After the physician is convinced that the pinworm infection is the problem, she advises on giving the same treatment and provides direction on how to clean up the environment to prevent further reinfection. The physician should have been convinced by which of the following facts?

A. The parent knew that reinfection was a possibility.

B. The parent had collected worms from bed linen and accurately described them.

C. The parent described symptoms of enterobiasis.

D. The parent had the child’s stool examined by her veterinarian who identified telltale eggs.

E. The parent noted that the family’s pet cat continued to sleep on the child’s bed.

Answers

[47.1] B. The egg stage is the stage transmitted from person to person. A larval form (A) is found inside the egg but does not escape to initiate infection until the egg is ingested. Adult forms (C) live in the intestine but are not the stage directly responsible for transmission of the infection. Cyst (D) and oocyst (D) stages are not a part of the life cycle of E. vermicularis.

[47.2] A. Mebendazole is the most appropriate of several available benzimidazole compounds to treat enterobiasis. This drug of choice is a highly effective, broad-spectrum antihelminthic. Metronidazole (B) is used to treat various protozoan infections, but is not efficacious in treating pinworms. Piperazine (C) is an anthelminthic that was used prior to the discovery of mebendazole to treat enterobiasis and is less effective, and its dose regimens are more complicated. Praziquantel (D) is effective in treating tapeworm and fluke (flatworms) infections but is not useful against pinworms or other nematodes. Chloroquine is a potent antimalarial drug but of no use against helminths.

[47.3] B. Finding and identifying adult pinworms is one way to make a definitive diagnosis. Reinfection (A) is a definite possibility but not convincing evidence that the child is actually infected. Symptoms described (C) are associated with enterobiasis but are only presumptive, not definitive, evidence of infection. A stool exam (D) is not an appropriate or effective method to diagnose enterobiasis. Cats (E) are in no way associated with transmission of infection.

MICROBIOLOGY PEARLS ❖ The egg (larvated) is the infective stage. ❖ The life cycle is direct, meaning that the adults develop from larvae without leaving the gastrointestinal tract. Adult worms are the primary cause of pathology. ❖ Pamental pamoate and mebendazole, a broad spectrum antihelminthic, are drugs of choice.

REFERENCES

Centers for Disease Control. DPDx. Laboratory identification of parasites of public concern. Enterobiasis. 2007. http://www.dpd.cdc.gov/dpdx/HTML/ Enterobiasis.htm. 

Centers for Disease Control. DPDx. Laboratory identification of parasites of public concern. Image Library. Enterobiasis. 2007. http://www.dpd.cdc.gov/dpdx/ HTML/ImageLibrary/Enterobiasis_il.htm. 

Medical Letter on Drugs and Therapeutics. Drugs for parasitic infections. New Rochelle, NY. 2004. http://www.medletter.com/freedocs/parasitic.pdf. This reference has been updated and “superseded by the special report Drugs for Parasitic Infections, which can be purchased (on-line) for $25.” This reference has been provided because it is a comprehensive and clinically useful reference that is regularly updated and could be of value to those who are involved in treating parasitic infections.

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