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Pinworms
(Pinworm Infection in Children and Adults, Enterobiasis)

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Medical Author:

Charles Patrick Davis, MD, PhD

Charles Patrick Davis, MD, PhD

Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

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Medical Editor:

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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Medical Editor:

Jay W. Marks, MD

Jay W. Marks, MD

Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

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What is pinworm infection?

Pinworm infection is an infection of the large intestine and anal area by a small, white parasite that resembles a "worm." The medical name for the parasite is Enterobius vermicularis, but it is commonly termed a pinworm in both the lay and medical literature. These parasites are also termed seatworms or threadworms, and the infections is medically termed enterobiasis or helminthiasis. Pinworms and other parasitic worms (as a group are termed helminths) feed off of the host animal by adsorbing nutrients from the host animal. Pinworm infections are the most common helminth infection that occurs in the US. The US Centers for Disease Control and Prevention (CDC) estimates about 40 million people are infected with pinworms currently in the US.

Who is at risk for getting pinworms?

Pinworm is the most common worm infection in the United States, and the majority of pinworm infections worldwide occur in temperate climates.

Pinworms in children

School-age children have the highest rates of pinworm infection. They are followed by preschoolers. Institutional settings including day care facilities often harbor cases of pinworm infection. Sometimes, nearly half of the children may be infected.

Pinworms in adults

Pinworm infection often occurs in more than one family member. Adults are less likely to have pinworm infection, except for mothers of infected children. However, adult sexual partners can transfer the eggs to each other.

What do pinworms look like (pinworm pictures)?

The pinworms are white, can be seen with the naked eye (no magnification) and are about the length of a staple (about 8-13 mm for female and 2-5mm for male worms). The eggs that are laid by the female worms are not visible as they are about 55 micrometers in diameter and are translucent (see Figure 1).

The male and female worms live for the most part within the rectum of humans but have a life cycle in humans that involves rectal/oral transmission (see Figure 2).

While an infected person is asleep, female pinworms leave the intestines through the anus and deposit eggs on the skin around the anus. This causes itching and irritation of the surrounding area; children especially will scratch the rectal/anal area, get eggs on their fingers or underneath their fingernails and transport the infective eggs to bedding, toys, other humans, or back to themselves. The eggs hatch into larval forms in the small intestines and then progress to the large intestine where they mature, mate, and progress to the rectal/anal area where females deposit about 10 to 15 thousand eggs.

Figure 1, picture of pinworm and pinworm eggs (magnified); (image courtesy of CDC.gov)

What does the lifecycle of a pinworm look like?

Figure 2, picture of the lifecycle of a pinworm (image courtesy of CDC.gov)

How is pinworm infection spread?

Pinworm infection is spread person-to-person. Within a few hours of being deposited on the skin around the anus, pinworm eggs become infective (capable of infecting another person). They can survive up to two weeks on clothing, bedding, or other objects. Infection is acquired when these eggs are accidentally swallowed, usually due to inadequate hand washing by the parents and children. However, eggs on bedding or other objects that are touched while the eggs are still viable can cause infection or reinfection of people.