Human infection with parasitic worms is more prevalent in the U.S. than many people realize, according to the Cleveland Clinic. Humans become infected with worms when soil contaminated with infected human or animal feces gets on food, hands or skin, or when infected undercooked meat or fish is consumed. Although some types of worms can only be seen under a microscope, others can grow to as long as a foot or more.
Gastrointestinal Discomfort
Although infection with parasitic worms does not always produce symptoms, gastrointestinal upset, including abdominal pain, nausea and diarrhea, may occur. Roundworms, or ascariasis, can grow to be the size of a pencil and cause mild abdominal pain that comes and goes. Heavy infestations can cause severe pain and vomiting if the worms block the intestines, according to the Cleveland Clinic. Nausea, vomiting, diarrhea and abdominal pain are among the first symptoms of trichinellosis, an infection that occurs after eating undercooked meat containing the larvae of the trichinella worm. As this infection progresses, many other symptoms can develop, including fever, chills, headache and muscle pain that results from larvae that migrate to muscle tissue and form cysts.
Signs of Anemia
Hookworms attach to the intestinal wall and suck blood, which can result in anemia from blood loss. Hookworm larvae enter the body through the skin of bare feet that come into contact with contaminated soil, the Cleveland Clinic explains. Fatigue, pale skin, shortness of breath and a rapid heart beat are some signs of anemia. Chronic, heavy hookworm infestation can cause severe anemia in children, pregnant women and people who are poorly nourished.
Itching
Pinworm also called seatworm, infects up to 30 percent of children worldwide, according to an article by Corry Jeb Kucik, LT, MC, USN and colleagues in the March 1, 2004 issue of the journal "American Family Physician." Although pinworm infection is rarely dangerous, a common symptom is intense anal and perineal itching that most commonly occurs at night. Itching results from the female worm traveling to the perineum to lay as many as 15,000 eggs. Itchy patches on the feet can occur after hookworm larvae enter through the skin.
Seizures
Tapeworms contracted from eating undercooked pork or beef can grow from 15 to 30 feet in length, according to Merck Manuals Home Edition. Certain types of undercooked freshwater fish can also harbor the infection. Although these ribbon-like worms commonly cause no symptoms, larvae can invade the intestinal wall and travel through the bloodstream to the brain, causing headaches, confusion and seizures.
