Enterobius vermicularis
Enterobius vermicularis is a small white worm with thread-like appearance. The worm causes enterobiasis. Infection is common in children.
Morphology
Male: The male measures 5 cm in length. The posterior end is curved and carries a single copulatory spicule.
Female: The female measures 13 cm in length. The posterior end is straight.
Infective stage
Infection is by ingestion of eggs containing larvae with contaminated raw vegetables.
Mode of infection
- By direct infection from a patient (Fecal-oral route).
- Autoinfection: the eggs are infective as soon as they are passed by the female worm. If the hands of the patient get contaminated with these eggs, he/she will infect him/herself again and again.
- Aerosol inhalation from contaminated sheets and dust.
Life cycle
Adult worm lives in the large intestine. After fertilization, the male dies and the female moves out through the anus to glue its eggs on the peri-anal skin. This takes place by night. The egg is 50x25 microns, plano-convex and contains larva. When the eggs are swallowed, they hatch in the small intestine and the larvae migrate to the large intestine to become adult.
Clinical presentation
The migration of the worms causes allergic reactions around the anus and during night it causes nocturnal itching (pruritus ani) and enuresis. The worms may obstruct the appendix causing appendicitis.
Diagnosis
- Eggs in stool: Examination of the stool by direct saline smear to detect the egg: this is positive in about 5% of cases because the eggs are glued to the peri-anal skin.
- Peri-anal swab: The peri-anal region is swabbed with a piece of adhesive tape (cellotape) hold over a tongue depressor. The adhesive tape is placed on a glass slide and examined for eggs. The swab should be done in the early morning before bathing and defecation.
INSTAGRAM
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