Parasitic roundworms can infect humans, causing numerous health problems. Differences in the route of infection and life cycle of each roundworm produce a different set of symptoms when the worms infect their host. Six of the most common parasitic roundworms that infect humans include Enterobius vermicularis (pinworm), Ascaris lumbricoides, hookworms, whipworms, Strongyloides stercoralis, and Trichinella spiralis.
Pinworms
Pinworms (Enterobius vermicularis) are the most common parasitic infection found in the United States and are most common in the warmer southern states. Pinworms are tiny threadlike roundworms that infect the colon and are easily spread among children due to poor hygiene habits. Infection can cause vaginal or anal itching that may be severe enough to interfere with sleep.
Ascaris lumbricoides
Ascaris lumbricoides is the largest parasitic roundworm, similar in size and shape to the common earthworm. The earliest symptoms may be mild abdominal pain, and sometimes you may see the worm in feces or vomit. Depending on the number of worms in the intestines, symptoms may be mild to severe. With heavy infection, the intestines can become blocked, causing severe pain and vomiting. Because the early part of the Ascaris life cycle occurs in lung tissue, pneumonia-like symptoms, such as difficulty breathing and coughing, can occur.
Hookworms
Hookworms can be picked up from the ground and can penetrate the skin on the soles of the feet, causing an itchy area at the entry site, sometimes called "ground itch." Common early symptoms of hookworm infestation include diarrhea, intestinal pain, cramping and nausea. As its name implies, the hookworm hooks into and attaches itself to the intestines to feed on intestinal blood. If the hookworm infection is severe enough, bleeding from this intestinal feeding can result in anemia, another symptom of hookworm infection.
Whipworms
Whipworms have a thin, whiplike shape. If the host is infected with a relatively low number of whipworms, symptoms of infection can be mild and the infection may be well-tolerated by the host. Heavier infections can cause more alarming gastrointestinal symptoms such as stomach pain, blood in the stool and poor nutrient absorption causing unintended weight loss. Young children are at risk for more severe symptoms, including bloody diarrhea and, in extreme cases, collapse of the rectum (rectal prolapse).
Strongyloides Stercoralis
A mild infection with the parasitic roundworm Strongyloides stercoralis may not cause any symptoms. More severe infection can cause burning pain in the abdomen and alternating cycles of diarrhea and constipation. In severe cases, symptoms may progress to weight loss, recurrent diarrhea and anemia from blood loss. In patients with a suppressed immune system, a condition called disseminated strongyloidiasis can occur if the worm is able to directly infect the intestines, which can result in severe pneumonia-like symptoms and possibly death.
Trichinella spiralis
Trichinella spiralis, the roundworm that causes trichinosis, can infect the muscles of meat-eating animals. Humans most often get trichinosis from eating undercooked infected pork. Unlike other roundworms, Trichinella spiralis encysts itself in the muscle, not the intestine of the host. Early signs of heavy Trichinella spiralis worm infection may mimic food poisoning but then progress to severe muscle and joint pain, sometimes referred to as "muscular rheumatism."
