Threadworms are highly contagious. They are easily spread by their tiny eggs being swallowed. The eggs can be transmitted through the air and breathed in. They can be picked off surfaces, such as door handles. They are then swallowed later when the fingers are placed in the mouth. The eggs stick together with a "glue" like substance which causes the itching sensation. When the infected area is scratched the eggs are transferred to the fingernails, then back to the mouth, continuing the cycle. There are often no symptoms but the common signs of threadworm infestation are persistant scratching of the bottom, restless sleep, loss of appetite and irritability.