Enterobius vermicularis - pinworms

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Enterobius vermicularis (pinworms)

Taxonomy, Common Name, Disease

 

* CLASS: SECERNENTEA

* SUBCLASS: RHABDITIA

* ORDER: RHABDITIDA

* SUBORDER: RHABDITINA

* SUPERFAMILY: OXYUROIDEA

* FAMILY: OXYURIDAE

 

Scientific name - Enterobius vermicularis

 

Common name - pinworm

Historical

The common name was derived from the typically slender, sharp-pointed

tails, especially of females.

Hosts

Humans are the only common host of E. vermicularis. Dogs and cats are

not hosts of pin worm. Other species of pinworm infect horses, mules,

zebra, sheep, goat, antelope, rabbits, rodents, elephant, and primates.

Distribution

Pin worm infections are common in humans throughout the world, but

survive best in the temperate zones.

Life Cycle

The adult worms feed on the mucosa of the large intestine. When

females are fully gravid they migrate from the anus and deposit fully

embryonated eggs in the perianal region. These eggs are the infective

stage and when ingested by man pass through the stomach to the

duodenum where they hatch. The immature worms remain in the small

intestine undergoing 2 molts. On becoming adults they migrate to the

large intestine where the females attach to the mucosa until they are

fully gravid. A single female may contain up to 20,000 fully

embryonated eggs (eggs with fully developed juveniles); the average is

about 10,000.

Symptoms-Pathogenicity

Ordinary infections cause relatively mild symptoms, usually intense

itching in the perianal region. Vaginitis may be caused by pin worm in

young girls. Massive infections may cause intestinal blockage but this

is rare. In children loss of appetite, insomnia and restlessness are

the usual symptoms associated with pin worm infections. Egg laying

begins about 50 days after infection.

Management

Prevention - Humans become infected by ingesting eggs from

contaminated fingers, food, or inhaling eggs in dust. Infections are

more common in members of the same family or in crowded living groups.

Good sanitation and personal cleanliness. Clothing and bedding should

be thoroughly laundered.

 

Treatment of Host - Vermox or Pyrantyl Pamoate are the drugs of

choice. Treating all members of a family should be considered when

control by drugs is undertaken.

 

Diagnosis - is by the use of the " NIH " swab. Eggs and worms adhere to

the sticky surface of the swab when it is applied to the perianal region.

Importance

In the United States it is estimated that infections in children

average about 35%. In some European countries it may reach 60%. The

rates of infection are lower in tropical areas. Worldwide it is

estimated that 500 million people are infected.

Characteristics

All pinworms have a conspicuous muscular bulb on the posterior end of

the esophagus. Both sexes of E. vermicularis have three lips

surrounding the mouth, followed by a cuticular inflation of the head.

Males have a single spicule which is 100 to 141 um long. Males are 1

to 4 mm long and have the posterior ends strongly curved ventrad. The

conspicuous caudal alae are supported by papillae. Females measure 8

to 13 mm long and have the posterior end extended into a long, slender

point. The vulva opens between the first and second thirds of the

body. When gravid, the two uteri contain thousands of eggs, which are

elongate-oval and flattened on one side, measuring 50 to 60 um by 20

to 30 um

References

 

1. Schmidt, G.S., and L.S. Roberts. 1989. Chapter 28. Order

Oxyurata: Pinworms. in Foundations of Parasitology. Times Mirror/Mosby

College Publishing. St. Louis. 750 pages.

2. Cox, F.E.G. 1993. Chapter 2. Parasitic Helminths. in Modern

Parasitology. Blackwell Scientific Publications, UK. 276 pages.

3. Levine, N.D. 1968. Nematode Parasites of Domestic Animals and of

Man. Burgess Publishing Company. Minneapolis. 600 pages.