What are the causes and symptoms of threadworm infection?
Threadworm infection is caused by Strongyloides stercoralis, a roundworm that lives in soil and can survive there for several generations. Mature threadworms may grow as long as 1–2 in (2.5–5 cm). The larvae have two stages in their life cycle: a rod-shaped (rhabdoid) first stage, which is not infective; and a threadlike (filariform) stage, in which the larvae can penetrate intact human skin and internal tissues. The infection is most commonly transmitted when a person comes into contact–usually by walking barefoot–with soil containing S. stercoralis larvae in their filariform stage. The threadlike larvae penetrate the skin, enter the lymphatic system, and are carried by the blood to the lungs. Once in the lungs, the larvae burst out of the capillaries into the patient’s main respiratory system. They migrate upwards–usually without symptoms–to the patient’s throat, where they are swallowed and carried down into the digestive tract. The filariform larvae settle in the small intestin
