The intestines are part of the human digestive system that connect the stomach to the anus. The main function of the intestines is the absorption of food products. This makes them susceptible to attack by parasites, organisms that grow and feed upon a host. The two main types of intestinal parasites are helminthes (multicellular worms) and protozoa (one-celled organisms). Approximately one-third of the world's population is infected with an intestinal parasite, according to statistics provided by the Centers for Disease Control and Prevention. Although many of the infections produce no symptoms, some can induce serious and chronic illness.
Pinworm
The pinworm (scientific name E. vermicularis) is a helminthes commonly found in the United States. Humans are the only host to the worm, so infections are common; approximately 30 percent of children worldwide are infected, according to American Family Physician. These small worms live in the large intestine and the adult females migrate to the perineum--the area between the anus and the genitals--to lay their eggs. The eggs are then transmitted from person to person through the fecal-oral route, meaning that food or water is contaminated with infected feces.
Pinworm infection can cause itching in the anal and genital region that can result in sleep disturbances. More serious disease can occur with symptoms including weight loss, urinary tract infection and appendicitis.
Giardia
Giardia--a protozoa named G. lamblia--is the most common intestinal parasite worldwide, according to American Family Physicians. Giardia is found in natural water sources, such as mountain streams, that have been contaminated with infected feces. Giardiasis, the illness caused by giardia, is often referred to as "backpacker's diarrhea" or "bever fever."
Humans are not the only host for giardia. This parasite can infect other animals, including beaver, cattle, dogs, rodents and sheep. Giardia, like pinworm, is transmitted through the fecal-oral route and can be a food-borne illness caused by contaminated food products.
Infection with giardia causes nausea, vomiting, diarrhea, malaise, gas, cramping and weight loss. In rare cases, giardia can cause reactive arthritis (inflammation of the joints) and rashes.
Hookworms
There are two different species of hookworms that use humans as hosts. A. duodenale is found in Europe, Africa, China, India and Japan; N. americanus is found in the United States and the Caribbean. Hookworms lay their eggs in the soil, and the larvae enter their hosts through open pores, skin and hair follicles. The larvae travel through the bloodstream to the lungs, where they climb up the bronchial tubes and are swallowed. The adult worms attach to the walls of the small intestines, where they feed on blood and produce more eggs.
Hookworm infections usually don't cause any symptoms, but they do cause a significant blood loss that can cause anemia, a low level of red blood cells and hemoglobin in the blood. In small children, a prolonged hookworm infection may result in mental retardation.
