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Enterobius vermicularis include worms like threadworms, pinworms, and seat worms. The pinworm, Enterobius vermicularis, is one of the most common nematode infections on the planet. Oxyuris vermicularis was the original name for E. vermicularis. The natural host for this virus is humans. They are found in some vertebrates, in addition to humans. Female pinworms are physically longer than male pinworms, which is one way to distinguish between the genders of pinworms.
Also, read: Ringworm
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Key Terms: Transmission, Infestation, gastrointestinal tract, Retro - Infection, oviposition, vermiform appendix, submucosa layer, Tadpole
Habitat
Adult worms (gravid females) dwell in the human caecum and vermiform appendix, where they stay until the eggs hatch. They usually stay on the mucosa's surface, but they might infrequently encyst in the submucosa layer. The pinworm dwells in the upper section of the colon and the lower part of the small intestine.
It is distributed throughout the world and causes the human infection enterobiasis. The pinworm, unlike many other intestinal parasites, seldom enters the circulation or any other organs other than the intestines. Disoriented pinworms can be detected in the vagina, and even more rarely in the uterus, fallopian tubes, liver, and peritoneum; however, the worms cannot survive in these locations for long.
Morphology
- The adult worm is small, white in color, spindle-shaped, and looks like a strand of thread.
- They can be seen with the naked eye.
- There is no true buccal capsule.
- The anterior extremity consists of a pair of cervical alae (wing-like extensions).
- A distinctive feature of this worm is that the posterior end of the esophagus is dilated into a prominent globular bulb/a double-bulb esophagus.
- The oral end features three lips and a cuticle that expands dorso-ventral like a bladder.
Male Worm
- Adult males have a length of 2-4 mm and a width of 0.1-0.2 mm.
- The body's posterior portion is bent, shorter, and has an exposed terminal copulatory spicule.
- Because the male worm dies shortly after fertilizing the females, it is rarely seen.
Female Worm
- The adult female is larger, with a length of 8-12mm and a width of 0.3-0.5mm.
- The worm's back end is exceptionally straight and draws out into a long, tapering, sharply pointed tail that is 1/3rd its length.
- Female reproductive organs are T-shaped and are paired.
- The uterus of the gravid female has a vast number of eggs, with an average of 11,105 eggs, which fill the female worm's entire body.
- After laying eggs, the gravid female dies within 2-3 weeks.
Eggs of Enterobius Vermicularis
- Humans are infected by embryonated eggs.
- The eggs are whitish and have a length of 50-60 meters and a width of 20-32 meters.
- Typically, they are plane convex, with one flattened side and one convex side.
- A thin, hyaline, transparent shell consisting of two layers of chitin surrounds the eggs.
- A coiled tadpole-like larva is contained within the egg.
- In a saturated salt solution, an egg may float.
- After 6 hours of exposure to ambient oxygen, the egg becomes infectious and more resistant to antiseptics.
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Life Cycle of Enterobius Vermicularis
It's critical to understand how pinworms enter our system before moving on to the lifespan phase. Pinworm eggs are spread through person-to-person transfer. This is now transmitted through the handling of infected surfaces like clothing, linen, curtains, and carpets. It's also possible that airborne eggs make their way into the body through inhalation. When eggs are transmitted to the mouth by fingers that have scraped the perianal area, self-infection can ensue.
It's important to remember that the entire life cycle of pinworm infective stages takes place in the human gastrointestinal tract. The eating of pinworm eggs is the first step in the process. Let's have a look at the various stages of the pinworm's life cycle, from conception through infection.
Life Cycle of Enterobius Vermicularis
Stage 1 – The Egg
The female pinworm lays eggs on the perianal skin, which is the border of the anus, after fertilization. Eggs are generally introduced through the mouth by hands that have scraped the perianal area. This pinworm produces irritation in the perianal area when it moves there. Infection can also arise if eggs come into contact with contaminated clothing, bedding, or other surfaces.
Stage 2 - The Larvae
Humans' tiny intestines are where the eggs hatch after they have been consumed. The larvae inside the eggs grow in 4 to 6 hours, depending on the climate, and the eggs become infective after that. The adult worms subsequently established themselves in the colon.
Stage 3 – The Adult
A month passes between the swallowing of eggs and the oviposition of adult females. Gravid (pregnant) females move outside the anus at night and oviposit while crawling on the anus's perianal skin. The Enterobius Vermicularis life cycle continues.
Retro - Infection
It's worth noting that an adult pinworm only lives for around two months. Pinworms live their whole life cycle as parasites inside the human body. The eggs are consumed from any source. Human intestines are where they grow and reproduce. Retro-infection occurs when newly born larvae travel back into the anus after hatching.
The deposition of eggs on the perianal skin or the rim of the anus causes retro-infection. The young pinworms mature into adults by crawling back into the anus. The process then repeats itself. It takes 6 hours for these eggs to develop and become infective in this situation.
Also, read: Human Health and Diseases
Modes of Transmission
- The only source of infection is infected, humans. There is no known extra-human reserve.
- Ingestion of eggs from contaminated fingers, which is regularly seen in youngsters, is one mechanism of transmission.
- Handling the children's contaminated nightwear.
- Airborne eggs included in the dust are inhaled.
- Infection with a retrovirus is mostly encountered in adults.
Things to Remember
- People can get sick by ingesting the embryonated eggs attached to their nails during perianal scratching.
- The female commonly dies after oviposition.
- The whole life-cycle completes within 2-13 weeks.
- Because air stimulates egg-laying, females exclusively lay eggs on the perineum.
- During copulation, males employ spicules to hold females in place. After fertilizing the female, the male dies immediately.
Sample Questions
Ques. Does Enterobius Vermicularis have a direct life cycle? (2 Marks)
Ans. Pinworms have a direct life cycle that involves the oral consumption of eggs that carry infective larvae. Humans are the only known host for Enterobius vermicularis, which has a simple one-host life cycle. Adults reside in the large intestine lumen. Gravid females move to the anal orifice at night and deposit semi-embryonated eggs in the perianal folds.
Ques. What is the lifespan of a pinworm? (2 Marks)
Ans. Pinworms have a lifespan of up to 13 weeks. Scratching an infected area might result in inadvertent ingestion, which can result in reinfection and a re-start of the pinworm life cycle. When pinworm larvae emerge from eggs on the anus, they might reinfect the gut from which they came.
Ques. What are the Symptoms of Pinworm Infection? (3 Marks)
Ans. The adult female goes down the intestines and exits the body through the anus four weeks after ingestion to deposit eggs. This now occurs at night. Once the task is completed, the worm dies and is thrown out by natural means. Itching may occur as a result of egg deposition, especially at night.
Pinworm infection normally has no symptoms, but the following are some markers of pinworm infection: Itching in the bottom of the foot at night, a loss of appetite, a moderate sense of unwellness, vaginal irritation, impatience, and behavioral changes are all symptoms to look out for. Worms and eggs can be seen in the feces and near the anus.
Ques. What is the infective stage of Enterobius vermicularis? (2 Marks)
Ans. Females travel out of the body at night and deposit eggs on the perianal skin. Within a few hours, the eggs become infective, and the life cycle is completed when the eggs are eaten and hatch, releasing the worm's larval form into the host's small intestine.
Ques. Why is perianal itching significant in the life cycle of pinworms? (2 Marks)
Ans. Anal pruritus is caused by sticky eggs and the presence of migratory pinworms. The eggs become highly infectious within hours and are spread when an infected individual scratches their perianal area. The eggs stick to your fingers and fingernails easily.
Ques. Who is prone to pinworm infection? (2 Marks)
Ans. Thumb-sucking babies, school-aged children, and their family members are all at risk of contracting pinworm illness. Pinworm infection is most common in children under the age of 18, persons who care for affected youngsters, and people who are institutionalised. The prevalence in these populations can be as high as 50%. The most frequent worm infection in the United States is pinworm.
Ques. Where are pinworms found in the body? (2 Marks)
Ans. Pinworms are white, round-shaped worms that live in the human colon and rectum. The eggs hatch later in the body's small intestine under favorable conditions. Pinworms are parasitic white worms that can survive in the human large intestine. They measure around a half-inch in length. Female pinworms leave the intestinal tract and lay their eggs on the skin around the anus as the infected person sleeps.
Ques. How do you test for pinworms? (2 Marks)
Ans. As soon as the person you believe has pinworms awakens, place the adhesive side of a piece of transparent tape to the skin surrounding the anus of the person you suspect has pinworms. The eggs adhere to the masking tape. You then bring the tape to your visit so that the doctor can examine it under a microscope for pinworms or eggs.
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