Internal parasites such as roundworms can infect the body in a variety of ways. The worms generally exist in warm, temperate climates. According to the Cleveland Clinic, initial roundworm infections are caused by unsanitary conditions, human carelessness and decreased hygiene levels. Pinworms and hookworms are a type of roundworm.
Pinworms
The most common worm infections in the United States are caused by pinworms, also known as Enterobius vermicularis. According to the Centers for Disease Control and Prevention, pinworms are transmitted to the human body through the fecal-oral route. A person might have feces on his hands and transfer the worms to the mouth while eating or drinking. Contaminated items such as food, clothing and other household items might also be touched and the worms can then be transported to the mouth and swallowed. The CDC reports pinworms can move from a person's anus and linger on household items for two to three weeks. The worms can also become airborne and breathed in. It takes about one month for pinworm larvae to grow into the size of adult worms.
Hookworms
Hookworms are a type of roundworm affecting nearly 740 million people worldwide, according to the World Health Organization. However, the condition remains largely controlled in the United States. Still, the most common type of U.S. hookworm is Necator americanus, reports the National Institute of Allergy and Infectious Diseases. Human feces pass hookworms onto the ground in unsanitary locations. During cool weather, the worms wiggle and wave their bodies in the air until contact and transmission with human skin is made. Hookworm infections are caused by transmission of larvae in the third growth stage through the soil. Larvae can enter directly into the skin through the feet, hands, arms or legs. While in the body, the worms can enter the lungs, are coughed up and swallowed. The hookworms enter the digestive tract, where eventually the worms stay in the lower intestine. Complications include severe blood loss and anemia.
Roundworms
All roundworms, or nematodes, are invertebrates. According to the Cleveland Clinic, some roundworms remain visible to the human eye while others can only be seen with a microscope. Additional roundworms include ascariasis, strongyloidiasis and trichinosis. Ascariasis spreads when infected human feces is mixed with soil. Children playing in dirt or fruits and vegetables covered with contaminated soil can cause infection. Strongyloidiasis infections occur directly through the skin, similar to hookworm infections. A person who ate raw or undercooked meat can suffer from trichinosis. The parasite can be found in pork, bear and other wild animals, according to MedlinePlus. Still, the disease is rare. Only about 40 cases of the disease occur annually.
