Source:  Roundworm    Tag:  pinworm disease
Roundworms are elongated, cylindrical individuals that may have evolved from flatworms. Roundworms or nematodes infect either the intestines or subcutaneous tissues.

Roundworms have a completed digestive tract.

The three most important roundworms that parasitize human beings are the Ascaris, the pinworm and the Trichinella worm.

The Ascaris lumbricoides is the most commonly encountered parasitic worm, infecting around 1.4 billion people worldwide.  It is a large roundworm, about the size of a large earthworm that lives in the intestinal tract.

Eggs lived in the soil and get into the body by human host swallowing infected food. They reenter the intestine, where they attach to the mucosa and suck blood for nourishment. Severe infections may cause intestinal bleeding, anemia or intestinal obstruction.

The small roundworm Enterobius vermicularis is usually called simply the pinworm because of its, small size which generally measures less than 1 cm in length.

Transmitted by the oral-fecal route, pinworms live in the intestine and usually cause no symptoms; however, in some patients the worm crawls onto perianal skin and causes intense itching.

Another small roundworm, Trichinella spiralis, causes a severe parasitic infection called trichinosis. The organism parasitizes not only humans but also a wide variety of animals.

Clinical appearance of these infections often lacks specific symptom and is rarely recognized by the infected person, even when causing significant health damage.

Intensity of infection, and thus morbidity is directly related to the number of worms harbored.