Roundworms, also known as nematodes, are a common cause of human parasitic infestations worldwide. Pinworms are the only common roundworm infestation in the U.S. Other roundworms including hookworms, threadworms, whipworms, Ascaris and Trichinella occur most often in people who have traveled to locations where these worms are common. The severity of illnesses caused by parasitic roundworms ranges from mild to life-threatening.
Pinworms
Enterobius vermicularis, or pinworms, live in the lower region of the large intestine. During sleep, the female worms crawl out of the rectum and deposit their eggs on the skin near the anus causing itching. Pinworms spread from person to person by accidentally ingesting worm eggs and most commonly affect young children.
Ascaris
Although uncommon in the U.S., the Centers for Disease Control and Prevention (CDC) reports Ascaris lumbricoides is the most common type of parasitic worm infestation worldwide. Ascaris worms live in the small intestine. Inadvertent ingestion of worm eggs from fecal contamination of your hands or food causes infestation. Stool from an infected person is the source of the eggs. Heavy infestation may cause abdominal pain or intestinal blockage, especially in children.
Hookworms
Two hookworms, Ancylostoma duodenale and Necator americanus, cause human infestation. Hookworms are transmitted through soil contamination rather than worm egg ingestion. The immature form of the worm, the larva, burrows into the skin of the foot and travels to the lungs. It migrates to the throat where it is swallowed. Hookworms attach to the wall of the small intestine where they mature and feed on blood from the intestinal wall. Heavy infestation may cause weight loss, protein deficiency and iron-deficiency anemia. While rare in the U.S., the CDC reports the estimated number of hookworm infections worldwide in 2002 was 1.3 billion.
Whipworms
Whipworms, Trichuris trichiura, inhabit the large intestine. Accidental ingestion of the worm eggs through fecal contamination of food or your hands leads to infection. The adult worms attach to the intestinal wall where they feed. Mild infestations are often asymptomatic. Heavy infestations may cause abdominal pain, anemia and diarrhea. A complication known as rectal prolapse--the lowest part of the large intestine protrudes out from the anus--may occur. Children most often develop this complication.
Threadworms
Threadworms, Strongyloides stercoralis, enter the body in the same manner as hookworms. The immature larval worms burrow through the skin, migrate to the lungs and throat and are swallowed. Threadworms live in the upper part of the small intestine. Threadworms are unusual in that they can repeatedly infect the same person, a process called autoinfection . Threadworm autoinfection can cause a heavy infestation called a hyperinfection wherein the worms migrate to organs outside the intestine including the liver, heart and brain. Threadworm infection symptoms include abdominal pain, nausea, vomiting, diarrhea and weight loss. Hyperinfection can cause intestinal blockage, bleeding, cough and shortness of breath.
Trichinella
The Trichinella spiralis roundworm is contracted from eating raw or undercooked meat from an infected pig. Horse, wild boar and bear meat are other sources of infection. Adult Trichinella worms reproduce in the small intestine giving rise to immature larval worms. The larval worms burrow through the intestinal wall and migrate to muscle tissue where they form cysts. Symptoms are most common as the larval worms migrate to muscle tissue causing fever, headache, abdominal pain, nausea and diarrhea. Muscle invasion may cause achiness and weakness. These symptoms often resolve as the larval worms are walled off in cysts within the muscle tissue.
References
- "Principles and Practice of Infectious Diseases, Sixth Edition"; Gerald L. Mandell, M.D., et al, Editors; 2004
- Merck Manual: Pinworm Infestation
- U.S. Centers for Disease Control and Prevention: Pinworm Infection
- Merck Manual: Ascariasis
- U.S. Centers for Disease Control and Prevention: Ascaris Infection
