Trichuris and Enterobius
On this page
Direct answer
Trichuris trichiura and Enterobius vermicularis are intestinal nematodes, the whipworm and the pinworm respectively. Trichuris is acquired by ingesting embryonated eggs and can cause rectal prolapse in heavy infection, while Enterobius causes perianal itching at night. The classic exam facts are the barrel-shaped whipworm egg with polar plugs and the cellophane tape test used to detect pinworm eggs.
What you must remember
- Trichuris egg: The barrel-shaped egg has a prominent polar plug at each end and is passed unembryonated in stool.
- Rectal prolapse: Heavy whipworm infection, mainly in children, can cause rectal prolapse because adult worms embed in the colonic mucosa.
- Enterobius eggs: Asymmetrically flattened eggs are laid on the perianal skin rather than passed in stool.
- Cellophane tape test: Sticky tape pressed to the perianal skin in the early morning collects eggs for microscopy.
- Pruritus ani: Nocturnal perianal itching is the classic symptom of enterobiasis, caused by female migration.
- Autoinfection: Eggs carried on fingers return to the mouth, which causes reinfection, so hand hygiene matters.
- Treatment: Albendazole or mebendazole treats both helminths, and a repeat dose after about two weeks is advised for Enterobius.
- Egg size: Trichuris and Enterobius eggs are of similar length, about 50 to 55 micrometres, so shape rather than size separates them.
Two worms, one hand-to-mouth route, different damage
Both worms are acquired by swallowing eggs, but they settle in different parts of the bowel. Their symptoms and diagnostic methods differ accordingly, which is why the pathway below separates the two worms at the stage of egg output.
- Ingestion: Trichuris eggs swallowed with contaminated food mature in soil before becoming infective. Enterobius eggs are swallowed after fingers touch perianal skin where the eggs were laid, so they can infect the same person quickly.
- Settlement: Trichuris adults embed their thin anterior ends in the caecum and colon, while Enterobius adults live mainly in the caecum and appendix.
- Damage: Heavy Trichuris infection can cause anaemia, dysentery and rectal prolapse, while Enterobius mainly causes itching and sleep disturbance with rare complications.
- Egg output: Trichuris eggs appear in stool, but Enterobius females migrate out of the anus at night to lay eggs on the perianal skin.
- Diagnosis: Stool microscopy detects Trichuris eggs, and the morning cellophane tape test detects Enterobius eggs.
- Treatment: Albendazole or mebendazole treats both, and the Enterobius cure needs a repeat dose after about two weeks to clear newly hatched worms.
Where the exam tries to catch you
Most mistakes come from using the stool for pinworm and mixing up the egg shapes of the three common nematodes.
- Trap: Using a stool sample to diagnose pinworm Correct: Enterobius eggs are laid on perianal skin, so the cellophane tape test is the right method.
- Trap: Calling Trichuris eggs like the mammillated Ascaris egg Correct: Trichuris eggs are barrel-shaped with polar plugs and are distinct from Ascaris eggs.
- Trap: Assuming rectal prolapse always comes from Trichuris Correct: whipworm is a classic cause in children, but prolapse also arises from chronic straining and other causes.
- Trap: Treating only the affected child for pinworm Correct: pinworm spreads among close contacts, so the whole household is treated together.
Frequently asked questions
Which egg shape identifies Trichuris trichiura?
Trichuris trichiura eggs are barrel-shaped with a prominent polar plug at each end and are passed unembryonated in stool. This shape separates them from Ascaris and hookworm eggs.
Which test detects Enterobius vermicularis eggs?
The cellophane tape test detects Enterobius vermicularis eggs, and it is usually performed early in the morning before bathing or defaecation. Stool examination is often negative because the eggs are laid on the perianal skin.
What causes rectal prolapse in trichuriasis?
Rectal prolapse in trichuriasis results from heavy infection, in which many whipworms embed in the rectal mucosa and cause chronic straining. It is most often seen in children with severe infection.
Which drug treats both Trichuris and Enterobius infections?
Albendazole and mebendazole treat both Trichuris trichiura and Enterobius vermicularis. Enterobius infection needs a repeat dose after about two weeks to clear reinfection from newly hatched worms.
Why are household members treated for pinworm?
Household members are treated because Enterobius eggs spread easily through bedding, clothing and fingers. Treating everyone together prevents the treated person from being reinfected by a relative who still carries worms.