Enterobius vermicularis

Presented by Sandra Thorbus & Samantha Todd

HostsO Definitive Host: Humans

O Not associated with socioeconomic status

Geographical Distribution

O WorldwideO Most common worm infection in the

United States & Western Europe.O In the United States, a study by the

CDC reported incidence rate of 11.4% among all ages, 33% among children.

O Prevalence in children as high as 61% in India, 50% in England, 39% in Thailand, 37% in Sweden, and 29% in Denmark.

MorphologyO Egg has five membranesO Eggs are translucent and are covered in a

material that allows them to stick to environmental objectsO Membrane makes the eggs “itchy”O Eggs have a thick shell that is flattened on one

sideO The eggs small size (50-60 micrometers)O May contain an embryo or fully-developed

larvaO Larvae molt twice before hatching

Enterobius vermicularis eggs

Larvae Morphology

Larvae grow to 140-150 micrometers in length

Larvae are smaller and more coiled than the adults

Molt twice before becoming adults

Adult Morphology

White, small roundworm with

cylindrical body surrounded by 3 layered cuticle

The female has a sharply pointed posterior end

(8-13 mm long x 0.5 mm thick)

Have alae on anterior part of body wall

Can lay up to 15.000 eggs/day

Male has a curled posterior end

measuring 2 to 5 mm long x 0.2 mm thick

Both sexes have three lips

Alae on Female

TransmissionHuman-to-human contact by

ingesting infectious eggs

Eggs remain viable in moist environment for up to three

weeks

Once eggs are deposited near anus they can contaminate other surfaces such as:

Fingernails

HandsClothing and bed linensThen onto food, water, furniture, toys, bathroom fixtures and pets.

PreventionO Wash hands after using the

bathroom and before preparing food. O Wash bedding and underclothing

frequently, especially those of any affected family members.

Life CycleEggs are ingested

Hatch in S.I.

Larvae emerge and migrate through small intestine to

colon

Molt twice to become adults

Gravid female attaches to intestinal mucosa in ileum,

cecum, appendix or ascending colon

Ingest colon contents until entire body is filled with

eggs

Life CycleGravid females migrate through the

colon towards the rectum at a rate of 12-14 cm/hour

Female emerges from anus and deposits eggs by

contracting and expelling,

dying and degrading,

or bodily rupture due to the host scratching.

The female comes out of the anus

so the eggs can be exposed to oxygen to mature

After laying eggs, the female becomes opaque and dies.

Under optimal conditions larvae

within the eggs will develop within

4-6 hrs. after being laid making them extremely infective

PathogenesisO Causes EnterobiasisO Retroinfection-larvae migrate back

up the bowel to the G.I. tractO Pinworms as seen in colonoscopy

SymptomsO Intense itching in the anal region,

especially at nightO Restless sleepO Infection can migrate to the vagina and

cause vaginal dischargeO Itching leads to secondary bacterial skin

infectionO Abdominal pain and nausea are

associated with high populationO Some are asymptomatic

DiagnosisO Itching around perianal region is

indicative of infectionO Worms are visible in the anal region,

especially 2 to 3 hours after sleep,O Look like tiny pieces of white thread

O Eggs are rarely seen in stool samples

“Scotch Tape Test”

Most reliable method to detect eggs

Piece of cellophane tape is placed sticky side down to the skin around the anus

Pinworm eggs will stick to the tape and then the tape can be viewed under a microscope

Test should be done immediately after the person wakes up in the morning before washing, going to the bathroom, or getting dressed since eggs may be removed during these processes.

TreatmentMebendazole or Albendazole commonly prescribed for entire family

OTC Pyrantel Pamoate

1 dose is given immediately, then wait two weeks for another dose. The second dose is to kill any adult worms that may have hatched in the meantime

ReviewO How many times do pinworms molt?

O What is the tell tale sign of a pinworm infection?

O What is one method of diagnosis?

O Where do females lay their eggs?

O How can you prevent pinworm infection?

Works CitedO http://www.ncbi.nlm.nih.gov/pubmed

health/PMH0002137/

O http://en.wikipedia.org/wiki/Enterobius

O http://animaldiversity.ummz.umich.edu/site/accounts/information/Enterobius_vermicularis.html