Enterobius vermicularis

Due to its long-pointed tail, which resembles a straight pin in the adult worm, Enterobius vermicularis is called a pinworm. It is also known as ‘Seatworm’. It was originally called Oxyuris vermicularis, discovered by Linnaeus in 1758, and the condition was for several years referred to as oxyuriasis. In ancient Egyptian mummified human remains and in DNA samples from ancient human coprolite remains from North and South America, it is known to be the oldest parasite identified and was recently discovered.


It can be found all over the world, but it is more common in temperate climates. In the United States, E. vermicularis is the most prevalent helminth infection. It is a contagious infection that is particularly prevalent in children.


The female worm is larger than the male and can exceed a length of 7 to 13 mm as a typical trait in nematodes, making the adult females clearly visible from an infected individual in the stools. Since they are so tiny, the adult males can be largely overlooked. The egg of the species on one side is oval but flattened. It has a thick and colorless shell and is 20 to 30 μm wide and weighs 50 to 60 μm in weight. Owing to the colorless shell of the embryonized eggs, larvae may be visible within the egg.

Morphology of Pinworm Ova


  • Enterobiasis
  • Pinworm or seatworm infection

Disease Sign and Symptoms

Most forms of enterobiasis are asymptomatic; perianal or perineal pruritus, however, is the most frequent sign. From slight scratching to acute pain, this varies. Symptoms tend to be the most problematic at night, and affected people often experience sleep disorders, restlessness, and insomnia as a result. The secondary bacterial infection of excoriated skin is the most frequent complication of infection. Folliculitis in adults with enterobiasis has been seen.

The movement of the gravid female out of the anus to lay her eggs in the perianal field at night is linked with other symptoms. While enterobiasis has been described in eosinophilic colitis, eosinophilia is rare in infected individuals. The naked eye will see eggs sticking to the skin around the anus. Pinworms do not lead to abdominal pain, but since they have been detected in tissue samples such as the appendix, they have, possibly erroneously, been linked to cases of appendicitis.

Severe lesions, which are typically limited to minute ulcers and moderate inflammation of the intestine, are rarely caused by the disease. About half of all patients experience stomach distress. In certain cases, the skin can break down and progress to a secondary bacterial infection with extreme scratching of the anus.

Life Cycle

The eggs hatch to release larvae when ingested by infected hands, food or drink. The larvae develop and grow in the upper small intestine within 5 to 6 weeks without any further migration into other cavities of the body i.e. the lungs). Male and female variants also occur. The female is 8-13 mm long and up to 0.6 mm in diameter, while the smaller male is 2-5 mm in length and 0.3 mm in diameter. In the distal small bowel, copulation occurs and the adult females stay in the large intestine where they can survive for up to 13 weeks (males live for only 7 weeks). Roughly 11,000 eggs can be produced by the adult female. To lay her eggs, a gravid female will migrate out of the anus.

The adult female will pass down the digestive system roughly 1 month after infestation of the gut and will leave the body via the anus. There she lays on the skin covering the anus a batch of several hundred eggs, usually during the night or early in the morning before light reaches the bedroom.

Extreme itching, particularly at night, often accompanies the laying of the eggs. In this way, by soiling their fingers and even collecting eggs from the bed linen on the fingers and under the nails, children will reinfect themselves. A constant source of contamination maintains the period of replication by moving the eggs to the mouth where they are swallowed again. Even if the conditions are appropriate, the eggs can remain viable for up to several days.

Enterobius vermicularis ova microscopic image

Disease Transmission

The infection is spread by ingestion or inhalation of embryonated ova through the fecal-oral pathway. Fomites (inanimate items that are infected by organisms) and from soiled fingertips, filthy bed linens, toilet seats, and clothes may also spread the disease. The disorder is present globally and travels widely through families and communities in direct contact with each other, such as in early childhood day care centers.

Laboratory Diagnosis

Pinworm infestations are diagnosed by identifying dead adult worms or their distinctive ova. The adult female worm appears in the perianal region as a tiny white “thread fragment.” The most effective diagnostic method is “Scotch tape” or “cellophane tape.” This is best done right after the individual defecates or bathes in the morning. The buttocks are extended and a small sheet of transparent or cellulose acetate tape is rubbed against the anal or perianal tissue several times. The strip is then put on a microscope slide with the adhesive side down. The tissue of the worms is striated transversely and is transparent and white.

Typically, stool monitoring for eggs is not beneficial, since only 5-15% of affected people would have good outcomes. In special occasions, E. Vermicularis eggs were found in cervical specimens (done for regular Pap smears), in urine sediments, or during colonoscopy, worms were observed.


Several anthelmintic therapies are effective against E. vermicularis, with a cure rate of more than 90%. Efficient regimens include mebendazole (100 mg), albendazole (400 mg), and pyrantel pamoate (11 mg/kg of base) administered as a single dose and then repeated after 14 days. Pinworm can quickly spread within a home, so the sick person’s whole family should be handled. Both bedding and clothes should be washed completely. When a pinworm disease is discovered, the same law can be extended to organisations.

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