Sunday 13 June 2010

Enterobius vermicularis (Pinworm)

Parasite (Intestinal Nematode)

Your kids wake up each morning with an itchy butt?? Perhaps they have a Pinworm (Enterobius vermicularis) infection. Pinworm might be considered to be the world’s most common human parasitic infection. Thought to be more common in cool and temperate regions where the climate doesn’t necessitate as frequent bathing and changing of clothing.

Infection is initiated by ingestion of eggs which migrate to and hatch within the cecum where they develop into adult worms. It takes about a month for the female worm to mature and begin egg production of her own. After the female has been fertilized, the male worms die off and may be passed in the stool. Gravid females may almost entirely be filled with eggs (See Photos).
The females migrate down the colon and out of the anus where they deposit their eggs on the perineal and perianal skin. Still under controversy is whether the female worms are able to migrate back to the intestine. This migration and resulting irritation (pruritus) causes an almost irresistible desire to scratch. While pinworm infections may be asymptomatic, itchiness is the most prevalent symptom reported. Eosinophilia may result, tissue invasion has been reported in a few cases and in females heavy infections may invade the genital tract. In children, the desire to scratch along with less vigilant hygiene, can result in re-infection and the infection of playmates through the oral-fecal route.

Worm Morphology;
The female worm measures 8 to 13 mm in length by 0.3 to 0.5 mm in width while the smaller male worm measures about 2 to 5 mm in length and 0.1 to 0.2 mm in width. Both male and female worms have bodies that quickly taper to a point (hence the name pinworm) however the female’s tale is straight while the male is curved at the caudal end.

Egg Morphology;
Microscopically, eggs appear to be shaped as miniature grains of rice, flattened on one side and measure 50 to 60 mm long by about 20 to 30 mm wide.

Paediatric patients presenting with non-specific complaints such as irritability or insomnia coupled with anal itching, should be examined for pinworm infection. Infection can best be diagnosed by using Scotch Tape™ or commercially available sticky paddles on which eggs and worms can be securely trapped. The optimal time to sample is in the early morning upon waking and prior to washing up for the day.
In the laboratory, the sticky tape is placed sticky side down onto a glass microscope slide and scanned at lower powers for eggs (or plate microscope -best for worms). Finding characteristic eggs and/or worms confirms diagnosis.
Female worms migrate on a sporadic basis so several (4 to 6) attempts may be necessary for conformation or dismissing as negative.

Mebendazole and Pyrantal Pamoate are effective in treating pinworm infections.

Epidemiology & Prevention;
Because infection is so common and easy to acquire, breaking the oral-anal route is the most effective way of preventing the infection. Better hygiene, frequent changing of bed sheets and night clothes as well as disinfection of toys, furniture and objects in close contact with those infected, reduce the risk of spread. The laboratory technologist is also at risk if the diagnostic sample is not handled appropriately.
Ultra-violet light, dry heat and chlorinated pools will kill Enterobius vermicularis.

Straight Tail of Gravid Female Enterobius vermicularis Worm
(Single egg outside of worm clinging to tail)

Higher Magnification of Worm Body Filled With Eggs

Yet an even Higher Magnification, outer wall of worm where writing appears above.
(Worm body is so packed with overlapping & stacked eggs that it almost appears opaque)

Three relatively clear, flattened rice shaped eggs appear in photo

Pinworm Egg in Fecal Concentrate X400

New; March 14, 2011 Haematoxylin & Eosin Sections of appendix from young child containing pinworms. The following photos wore taken using the Leica DMD 108 microscope,

Above; Four worms in transverse section seen in lumen of appendix. (X100)
(click on photo to enlarge for better viewing)
  1. Lower left worm female showing ovaries containing developing pinworm eggs
  2. Central worm has ruptured wall
  3. All four worms have characteristic projections called 'alae' which on the worm furthest to the right I've highlighted with arrows.
  4. All four worms have darker purple structure which is the intestine. The lumen of the intestine appears somewhat as an X-shape.
(click on photo to enlarge for better viewing)
Above; Female worm in transverse section showing two ovaries with developing eggs. Single projection (alae) appears in frame of photo on right side of worm. Intestinal cross-section seen in lower right of worm's interior. (X400)

(click on photo to enlarge for better viewing)
Above; Worm cut in somewhat a longitudinal section. Most probably appears to be anterior end of worm showing structure of which I am unsure. This might be the esophagus or the median bulb cut somewhat at an angle. Two 'alae' are also seen at bottom left-of-center and top right-of-center of worm. (X400)

New; February 2012
I decided to add these photos here rather than place them in a new post as I had not photos showing the entire worm and though this might further add to the subject.

These pinworm specimens were obtained not from a adhesive tape prep from around the anus but rather taken during a colonoscopy on an adult male. The pinworm generally makes it's home in the large intestine and cecum.

Female Pinworm showing buccal cavity, esophagus and median bulb.
(Inset is the pointed tails of the female worm (thus the name 'pin'worm)
Nikon Camera 250X -(click on any photo to enlarge for better viewing)

As Above; Female with Buccal Cavity, Esophagus and Median Bulb visible.
Wet Preparation direct from colonoscopy material: (DMD-108 Microscope X250)

Female Pinworm (Entire) (Micron Scale Bar in upper right corner of photo)
Worm measured 2.65 cm in length & 180 µm at widest point of body
(Taken with DMD-108 Microscope X100)

Male Pinworm distinguished by it's curved caudal end/tale not all that convincing in this photo in which the worm is not straight but loops in the centre.
(DMD-108 Microscope X250)

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