Enterobius vermicularis - Introduction, Classification, History, Habitat, Morphology

Introduction to Enterobius vermicularis

Enterobius vermicularis is a common intestinal parasitic nematode (roundworm) that causes pinworm infection or enterobiasis. It is also known as threadworm, pinworm, or seatworm. This infection is most common in children and is transmitted via the fecal-oral route.

Although the parasite occurs exclusively in humans, infections have been reported from bonnet macaque.

Classification of Enterobius vermicularis

The classification of Enterobius vermicularis is as follows:

Kingdom: Animalia

Phylum: Nematoda

Class: Chromadorea

Order: Rhabditida

Family: Oxyuridae

Genus: Enterobius

Species: vermicularis

History of Enterobius vermicularis

The life cycle of the Enterobius vermicularis parasite was first described in 1865 by Leuckart.

Habitat of Enterobius vermicularis

The gravid female Enterobius vermicularis reside in the large intestine. The pinworm remains attached to the vermiform appendix, mucosa of the caecum, and adjacent parts of the large intestine.

Morphology of Enterobius vermicularis

The significant morphological forms of Enterobius vermicularis include:

• Adult worm

• Egg (infective form)

Adult worm

• adult Enterobius vermicularis worms are white, small, spindle-shaped and thread-like

• visible to the naked eye

• absence of true buccal capsule

• has a pair of wing-like expansions called cervical alae at the anterior end

• presence of a conspicuous double-bulb esophagus

Male

• adult Enterobius vermicularis male measures 2 to 5 mm long and 0.2 mm thick

• has a sharply curved but blunt posterior end with a conspicuous terminal copulatory spicule

• die immediately after fertilizing females, so rarely seen in samples

Female

• adult Enterobius vermicularis female measures 8 to 13 mm long, and 0.5 mm thick

• straight with a sharply pointed posterior end

• presence of paired and T-shaped reproductive organs

• uteri fill up the entire length of the female parasite

• each gravid female’s uteri can contain 4,600 to 16,900 eggs with an average of 11,000

• lives upto 2 months

Infective form

Eggs

• eggs of Enterobius vermicularis are an infective form of the parasite

• are translucent and non-bile stained

• measures 50 μm to 60 μm in length and 20 μm to 32 μm in breadth

• typically planoconvex – with one side convex and the other side flattened

• the eggshell is transparent and hyaline

• each egg encases a coiled larva or a developing embryo

• small size and transparency of the eggs make them invisible to the naked eye except if eggs are clumped into thousands