Enterobius vermicularis
Enterobius vermicularis, adult female
Enterobius vermicularis, the pinworm, is a nematode and the cause of enterobiasis. Humans are thought to be the only natural host. Children are classically infected from ingestion of embryonated eggs, especially in the day-care setting.
The adult female E. vermicularis is 8 to 13 millimeters long and has a slender pointed tail (from which the name "pinworm" comes). Both male and female worms have lateral alae that are most noticeable in the cephalic region. They also have a prominent bulbous esophagus. When seen in tape preparations, the female is generally gravid, containing numerous eggs.
Enterobius vermicularis, eggs, embryonated and hatching
These photos show the characteristic eggs of Enterobius vermicularis, commonly known as pinworm. They measure 50 to 60 micrometers in length, by 20 to 30 micrometers in width. Pinworm eggs are usually partially embryonated when laid, and become fully embryonated and infective within 4 to 6 hours. Note that you can see a developing larvae within each egg in these images, indicating that the eggs are now infective. Photos courtesy of Dr. Kara Levinson and Dr. Peter Gilligan. Shown here also are images of a hatching egg taken by Emily F. and Felicity in my lab. Fun!
Enterobius vermicularis, eggs, unembryonated
These photos show the characteristic eggs of Enterobius vermicularis, commonly known as pinworm. They measure 50 to 60 micrometers in length, by 20 to 30 micrometers in width. Pinworm eggs are unembryonated or partially embryonated when laid, and become fully embryonated and infective within 4 to 6 hours. These eggs are unembryonated/partially embryonated.
Enterobius vermicularis, adults in tissue
The adult worms can be found in the cecum, appendix, or colon where they mature over a 3–4-week period. The gravid female/s will travel to the anus during the nighttime and lay the partially embryonate eggs where they will fully embryonate and become infectious in approximately 4–6 hours. The female may also unintentionally wander ectopically to the appendix, biliary tree, or even the vagina, ending up in the uterus or fallopian tubes.
On histopathology, E. vermicularis can elicit inflammation, especially eosinophilic, and create small ulcers in the intestinal mucosa. A granulomatous response can result from dead/degenerating worms, even leading to lumen obstruction and appendicitis. The sectioned worms will display a thick cuticle with prominent lateral alae (arrows, labeled below). The musculature is platymyarian (wide and shallow) with 2–3 muscle cells per quadrant. If gravid females are present and sectioned, the characteristic eggs (asymmetric; flattened on one side) may be identifiable.
You can explore the WSI of Enterobius vermicularis in tissue HERE.
