ENTEROBIUS VERMICULARIS  


Phylum:- Nemathelminthes
Class:- Nematoda 
Common Name:- Pinworm, Threadworm. 

HABITAT:

The adult worm lives in the caecum, appendix, and cotton of human beings where they remain until the eggs are developed.

MORPHOLOGY:-  

Adult Worm:-

  • It is small and white in color.
  • It is spindle-shaped and as a short piece of thread.
  • Wing like expansion cervical alae are present at the anterior end. There is no buccal cavity. 
  • The posterior end of the esophagus dilated into the globular bulb.
  • The presence of a double bulb esophagus is a characteristic feature of the worm.

Male:

  • It measures 2-5mm in length and 0.1-0.2 mm in breadth.
  • Posterior a third of the body is curved and contains a copulatory bursa.
  • It usually dies after fertilizing a female. 


Female:

  • It measures 8-12 mm and 0.3-0.5mm in breadth. 
  • The posterior third of the body is pointed like a pin is called pinworm.
  • The female is oviparous and the grand female after oviposition dies with 2-3 weeks.


Eggs:-

  • The eggs are colorless and plano-convex in shape. 
  • Measurement :- 50-60um in length and 30 um in width. 
  • It is surrounded by a clear cell. 
  • The egg contains coiled tadpole-like larva.


LIFE CYCLE:

Humans are only reservoirs of E. vermicularis and no intermediate is lost is required.
Each of the egg newly laid on the perineal skin containing a tadpole-like larva.
It completes its development in the 24-36 hours in the presence of oxygen. 

Infection occurred by the ingestion of eggs.
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The egg cells are dissolved by the digestive juices and larva skip In the small intestine where they developed into an adult worm.
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After the worms become sexually mature, the adult male and female worm fertilized. 
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The gravid female than migrate from small intestine down to the caecum and colon and remain there until the eggs developed.
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The fertilized female then goes down to the rectum and works it way out of the anus during the night to deposit eggs on the perianal skin. 
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The life cycle is thus repeated again. It requires 2-4 weeks time to complete the Total life Cycle. 

MODE OF INFECTION:- 

  • Children's are usual victims and familiar infection is common.
  • Transmission is effected from one person to another by the ingestion of eggs.
  • The first infection is either contagious from close association.
  • Due to contaminated food and drinks.
  • The person handling the nightclothes of the infected patient contract the infection.
  • Auto infection maybe occur.
  • There is also a possibility of infection being airborne especially in an infected place.
  • Retroinfection- In retrograde infection the larva hatch out in parental skin and migrate back through the anus to caecum to develop there.


PATHOGENESIS / CLINICAL FEATURES:- 

  • The infection of pinworm is known as Enterobiasis. It causes- 
  • Perianal pruritus: It is related to the egglaying activity of the womb.
  • Nocturnal enuresis.
  • Pinworm rarely invades the female genital tract and causes bulbogenitis, salpingitis and pelvis granuloma. 
  • It may cause appendicitis.


LAB DIAGNOSIS:- 

1. Stool Examination.

  • Eggs maybe found as feces.
  • Adult females worm may be found in Faeces. 


2. Inspection of the anal region at the time of itching may reveal gravid female.

3. Perianal swab method/cellophane tape test:-

It is used for egg examination. It is advised to take swabs in the morning. Egg deposited in perineal region is determined by applying cellulose acetate tape. The egg stick to the cellophane tape. This tape is placed on a microscope slide examination.  

TREATMENT:

Mebendazole.
Pyrantel pamoate.

PREVENTION:

  • Health education on personal and community hygiene controls the spread of pinworm infection. 
  • Children should keep fingers nails short.
  • Bed linens & towels should be washed.