Threadworm infection is spread when the eggs are swallowed by uninfected individuals. The threadworms lay eggs around the anus at night, which results in intense itching. When scratching the eggs can become stuck beneath the fingernails.
From there the eggs may be transferred upon touch to other surfaces including bedsheets, other peoples hands, food and clothing. As the eggs can stay alive for 2 weeks on other surfaces outside of the body they can easily be picked up by other individuals who then swallow them and become infected.
People can also get threadworms again after they have been treated if they scratch the anus and then transfer the eggs into their mouth. This is known as reinfection and is why it is very important to regularly wash hands following threadworm infection.
