Question

Which of these may feature auto infection?

• A. Ancylostoma
• B. Enterobius
• C. Ascaris
• D. Paragonimus

Hint:

Enterobius (pinworm) causes perianal itching, and scratching plus hand to mouth contact lets the same person reinfect themselves.

Answer 1

The Correct Option is B

Auto infection means the parasite completes a fresh cycle inside the very same person who is already infected, without needing to mature outside the body first. Let's check each worm listed.

1. Ancylostoma: Hookworm eggs must hatch and develop into infective larvae in soil over several days before they can penetrate skin, so the same host cannot reinfect themselves right away.
2. Enterobius: The female pinworm lays eggs around the anus at night, causing itching. Scratching carries eggs to the fingers and then to the mouth, and eggs can also hatch on the perianal skin and crawl back inside. Both routes reinfect the same host directly, so this fits auto infection.
3. Ascaris: Eggs passed in stool need two to three weeks in soil to become infective, so there is a mandatory external maturation step before reinfection.
4. Paragonimus: This lung fluke needs a snail and then a crab as intermediate hosts, and humans get infected only by eating undercooked crab, so it cannot cycle back inside the same person directly.

The correct option is Enterobius, since its eggs can reinfect the same host either through hand to mouth spread or through retro infection, without any outside maturation step.

Let's summarize:

• Auto infection needs no outside soil or intermediate host step, the parasite cycles straight back into the same person.
• Hookworm, Ascaris and Paragonimus all need an outside maturation or intermediate host step, so they cannot do this.

So Enterobius vermicularis is the worm that may feature auto infection.