Enterobius Vermicularis Life Cycle

In the subject of biology, we study about worms and germs. You may have heard about Pinworms, threadworms, or seat worms. In biology, the classification is based on scientific names. So, the pinworm scientific name is Enterobius vermicularis. These worms fall under the family Oxyuridae and order Ascaridida. These worms are popular as human worms.  Primarily, they are parasites found in the intestines of human beings. You can find them more in children. Other than human beings, these worms are also found in some vertebrates. Here, we shall study about pinworm life cycle and the infections caused by these worms.

Enterobius vermicularis or pinworm is one of the most prevalent nematode infections in the world. The original name of E. vermicularis was Oxyuris vermicularis. Human beings are the natural host for this infection. Children are more prone to such infestations. The eggs of worms pass into the human body through the transmission. Transmissions occur commonly in people who live in crowded environments. It is noteworthy that transmission occurs within families.

In appearance, the worms are tiny, thread-like and whitish. The worm got its name after its typical pin-like tail present on the posterior part of the female worms. One point of differentiation between the pinworm genders is that the female pinworms are physically longer than male pinworms. Female pinworms may measure almost 13 mm, while male pinworms measure up to 5 mm in size. (Ref.Fig.1). According to the name, an infection caused by pinworms is sometimes referred to as Oxyuriasis; otherwise, it is known as enterobiasis.  

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Infective Stage of Enterobius Vermicularis

Before we move to the lifecycle section, it is essential to know how pinworms enter our system. The eggs of pinworms are ingested through person-to-person transmission. Now, this transmission happens due to the handling of contaminated surfaces such as clothing, linen, curtains, and carpets. It may also occur that airborne eggs find their way through inhalation. Sometimes, self-infection may occur if eggs are transferred to the mouth by fingers that have scratched the perianal area.

It is essential to note that the complete life cycle of pinworm infective stages takes place in the gastrointestinal tract of human beings.  The process starts with the ingestion of pinworm eggs. Let us have a look at the different stages in the life cycle of pinworm up to the final infection.

1 – Ingestion Stage

The life cycle within a human body begins for this parasite when eggs are ingested. After ingestion, larvae hatch from the eggs in the small intestine. The adults then migrate to the organ known as the colon. Adults mate in the colon. The males die after mating. This ingestion is through not-so hygienic conditions. School-going children and pre-school children are the most likely to get pinworm infection.

2 – Migration Stage

After the eggs of the pinworm are ingested and the larvae hatch, they travel through the stomach to the large intestines.  Along this route, the larvae grow further and reach sexual maturity. Adult female pinworms then move from the intestines to the anal area. Here, the females lay more eggs. It is essential to note that the egg-laying process typically happens in the middle of the night or early in the morning.

3 – Infection Stage

Female pinworms migrate to the anus in the night and deposit eggs in the perianal area. The females die after laying their eggs. The period from ingestion of infective eggs to the deposition of eggs by females takes approximately one month. The larvae develop, and the eggs become an infection in 4 - 6 hours.

Retro - Infection

Note that an adult pinworm lives for around two months. The entire lifecycle of pinworms exists inside the human body as they are parasites. The eggs are ingested from anywhere and by any source. They develop and reproduce inside the intestines of human beings. Sometimes, newly hatched larvae may migrate back into the anus, and this act is known as retro-infection.

Retro-infection happens with the deposition of eggs on the perianal skin or the rim of the anus. The juvenile pinworms crawl back into the anus and mature into adults. This way, the process repeats itself. In this case, it takes 6 hours for these eggs to grow and become infective.