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

Step 1: Understanding the Question:
Auto infection means a person keeps reinfecting themselves with a parasite without the eggs or larvae having to leave the body and mature outside first. We need to pick the parasite among the options where this can happen.

Step 2: Key Concept:
Enterobius vermicularis, the pinworm, is the classic example of auto infection among the common intestinal worms. The gravid female migrates out through the anus at night to lay her eggs on the perianal skin, and this causes intense itching.

Step 3: Detailed Explanation:
When the child or adult scratches the itchy perianal area, the sticky eggs get caught under the fingernails.
If the hands then touch the mouth, or food is handled with unwashed hands, the eggs are swallowed again, completing a new cycle inside the same host, this is hand to mouth auto infection.
A second route also exists called retro infection, where eggs hatch right on the perianal skin and the newly hatched larvae crawl back up through the anus into the rectum to mature there, without ever leaving the host.
Because of this, Enterobius infection tends to persist and spread easily within a household even with treatment, unless hygiene measures are also followed.

Step 4: Why the other options are wrong:
Ancylostoma, the hookworm, has infective filariform larvae that must develop in warm moist soil for days before they can penetrate human skin, so there is no way for a freshly passed egg to reinfect the same person directly.
Ascaris eggs passed in stool need about two to three weeks of development in soil to become infective, so they cannot cause auto infection either.
Paragonimus, the lung fluke, has a complex life cycle needing a snail and then a crab or crayfish as intermediate hosts before humans can get infected by eating undercooked crab meat, so direct auto infection in the same host is not possible.

Step 4: Final Answer:
Enterobius vermicularis is the correct answer, since both hand to mouth spread and retro infection allow it to reinfect the same host repeatedly.