Enterobius vermicularis, known as the pinworm or seatworm, is a roundworm parasite that has worldwide distribution and is commonly found in children. The adult female worm migrates out of the anus, usually at night, and deposits her eggs on the perianal area. The adult female (8 to 13 mm long) is occasionally found on the surface of a stool specimen or on the perianal skin. Since the eggs are usually deposited around the anus, they are not commonly found in feces and must be detected by other diagnostic techniques. Diagnosis of pinworm infection is usually based on the recovery of typical eggs, which are described as thick-shelled, football-shaped eggs with one slightly flattened side. Each egg often contains a fully developed embryo and will be infective within a few hours after being deposited.
The most striking symptom of this infection is pruritus, which is caused by the migration of the female worms from the anus onto the perianal skin before egg deposition. The sometimes intense itching results in scratching and occasional scarification. In most infected people, this may be the only symptom, and many individuals remain asymptomatic. Eosinophilia may or may not be present.
Infections tend to be more common in children and occur more often in females than in males. In heavily infected females, there may be a mucoid vaginal discharge, with subsequent migration of the worms into the vagina, uterus, fallopian tubes, appendix, or other body sites including the urinary tract, where they become encapsulated (1–8). Although tissue invasion has been attributed to the pinworm, these cases are not numerous. Symptoms that have been attributed to the pinworm infection, particularly in children, include nervousness, insomnia, nightmares, and even convulsions. In some cases, perianal granulomas may result (3).
In one report, a homosexual man presented with severe abdominal pain and hemorrhagic colitis, eosinophilic inflammation of the ileum and colon, and numerous unidentifiable larval nematodes in the stool. Using morphologic characteristics and molecular cloning of nematode rRNA genes, the parasites were identified as larvae of E. vermicularis; these larvae are rarely seen and are not thought to cause disease. The authors stated that occult enterobiasis is widely prevalent and may be a cause of unexplained eosinophilic enterocolitis (9).
The most widely used diagnostic procedure for pinworm infection is the cellulose tape (adhesive cellophane tape) method (5, 10–14) (Fig. 5.1 to 5.3). Several commercial collection procedures are also available. Specimens should be obtained in the morning before the patient bathes or goes to the bathroom. At least four to six consecutive negative slides should be observed before the patient is considered free of infection. Occasionally adult female pinworms are seen on the tapes or swabs.
Figure 5.1 Collection of Enterobius vermicularis eggs by the cellulose tape method. (Illustration by Sharon Belkin.) doi:10.1128/9781555819002.ch5.f1
Figure 5.2 Diagram of a commercial kit (Evergreen Scientific) for use in sampling the perianal area for the presence of pinworm (E. vermicularis) eggs. On the left is the vial containing the sampler, which has sticky tape around the end. Once this is applied to the perianal area and eggs are picked up on the tape, the label area is placed at one end of the slide. The sticky tape is rolled down the slide and attaches to the glass. This device is easy to use and provides an area sufficient for adequate sampling. A minimum of four to six consecutive negative tapes are required to rule out a pinworm infection; most laboratories are accepting four rather than requesting the full six. (Illustration by Sharon Belkin.) doi:10.1128/9781555819002.ch5.f2
Figure 5.3 (Top) Enterobius vermicularis (pinworm) eggs seen in a Scotch tape preparation; note the football-shaped eggs with one side a bit flatter than the other. In some preparations, eggs are seen that contain fully developed larvae; such eggs are infective. (Middle) Adult female pinworm found on a collection device. Note the large, round esophageal bulb. (Bottom) Adult female pinworm, enlarged anterior end. Note the cephalic expansions around the end of the head, as well as the large, round esophageal bulb. doi:10.1128/9781555819002.ch5.f3
Collection of the Specimen
1. Place a strip of cellulose tape on a microscope slide, starting 1/2 in. (1 in. = 2.54 cm) from one end and running toward the same end, continuing around this end lengthwise; tear off the strip flush with the other end of the slide. Place a strip of paper, 1/2 by 1 in., between the slide and the tape at the end where the tape is torn flush.
2. To obtain the sample from the perianal area, peel back the tape by gripping the label, and with the tape looped (adhesive side outward) over a wooden tongue depressor held against the slide and extended about 1 in. beyond it, press the tape firmly against the right and left perianal folds.
3. Spread the tape back on the slide, adhesive side down.
4. Write the name and date on the label.
Note Do not use Magic transparent tape; use regular clear cellulose tape. If Magic tape is submitted, a drop of immersion oil can be placed on top of the tape to facilitate clearing.
Examination
Lift one side of the tape, apply 1 small drop of toluene or xylene, and press the tape down on the glass slide. The preparation will then be cleared, and the eggs will be visible. Examine the slide with low power and low illumination.
The anal swab technique (15) is also available for the detection of pinworm infections; however, most laboratories use the cellulose tape method because it eliminates the necessity for preparing and storing swabs. At least four to six consecutive negative swabs should be obtained before the patient is considered free of infection.
Collection