A threadworm infection is usually passed from person to person as a result of poor personal hygiene.
A female threadworm can lay thousands of tiny eggs around the anus or vagina. While laying eggs, the female threadworm also releases a mucus that causes itching.
Scratching the anus or vagina, or wiping them after going to the toilet, can result in the eggs becoming stuck on your fingertips or under your fingernails.
The eggs can then be transferred to your mouth or onto food or objects, such as toys and kitchen utensils. If someone else eats the contaminated food or touches the contaminated object and then touches their mouth, they will become infected.
After the eggs have been swallowed they will pass into a person's intestine, where they will hatch. After about two weeks, the threadworms will have grown into adults, will reproduce and the cycle of infection will start again.
Transferring eggs
Threadworm eggs can be transferred from your anus (or vagina) to anything that you touch including:
- bed sheets and bed clothes
- flannels and towels
- children’s toys
- kitchen utensils
- toothbrushes
- furniture
- kitchen or bathroom surfaces
Threadworm eggs can survive on surfaces for up to three weeks.
They can be swallowed after touching contaminated surfaces and they can also be breathed in and then swallowed. This can happen if the eggs become airborne, if, for example, you shake a contaminated towel or bed sheet.
Poor hygiene
Threadworm infections are common in young children because they often forget to wash their hands after going to the toilet.
Children can also have prolonged threadworm infections by swallowing new eggs. Because they come into contact with other children and share toys, it's easy to become re-infected.
Threadworms are often found in families, particularly in crowded conditions. The risk of transmission between family members can be as high as 75%.
Animals and pets
Threadworms only infect humans and can't be caught from animals. However, there's a small risk that threadworms can be caught from household pets if the animal’s fur becomes contaminated with eggs during petting or stroking from an infected person. The eggs could then be passed to another human if they touch the animal’s fur.
