Helminths causing infection of large intestine

Question 1

Habitat of Enterobius vermicularis adult worm

Answer 1

in the caecum and adjacent portion of ascending colon

Question 2

State all the common other names for E. vermicularis

Answer 2

Pinworm & Seatworm

formerly called Oxyuris vermicularis

Question 3

E. vermicularis affects which age group mostly?

Answer 3

Children

Question 4

Disease of E. vermicularis

Answer 4

Enterobiasis (Pinworm infection)

Question 5

Adult morphology in Enterobius vermicularis

Answer 5

• The adults are short, white, fusiform worms with pointed ends
• The mouth is surrounded by 3 wing-like cuticular expansions (cervical alae), which are transversely striated

Question 6

Female worm morphology in E. vermicularis

Answer 6

• The female is 8–13 mm long and 0.3–0.5 mm thick
• Its posterior third is drawn into a thin pointed pin-like tail
• The worm is oviparous

Question 7

Male worm morphology in E.vermicularis

Answer 7

• The male worm is 2–5 mm long and 0.1–0.2 mm thick

* Its posterior end is tightly curved ventrally and carries a prominent copulatory spicule

Question 8

The structure of egg in E.vermicularis

Answer 8

• Colorless and not bile-stained
• Planoconvex shape, being flattened on one side and convex on the other
• Measuring 50–60 μm by 20–30 μm
• Egg shell is double layered
• Outer albuminous layer makes the eggs sticky
• It contains a coiled embryo, which is fully formed and infectious few hours after being deposited on the skin

Question 9

Natural host in E.vermicularis is ?

Answer 9

Human

Question 10

Infective form in E.vermicularis

Answer 10

Embryonated eggs

Question 11

Mode of infection in E.vermucalaris

Answer 11

Man acquires infection by ingesting embryonated eggs containing larva by means of:

1. Contaminated fingers
2. Autoinfection

Question 12

Life cycle of E.vermuclaris

Answer 12

• Eggs laid on perianal skin are swallowed and hatch out in the intestine.
• It takes from 2 weeks to 2 months to develop the gravid female.
• The gravid female migrates down the colon to the rectum.
• At night, when the host is in bed, the worm comes out through the anus and crawls about on the perianal and perineal skin to lay its sticky eggs.
• The female worm may wander into the vulva, vagina and even into the uterus and fallopian tubes, sometimes reaching the peritoneum.
• The male usually dies after mating and is passed in the feces.
• The eggs are infrequently found in feces, as the female worm lays eggs in the perianal area and not the rectum.

Question 13

Auto infection in E. vermicularis

Answer 13

• Ingestion of eggs due to scratching of perianal area with fingers leading to deposition of eggs under the nails.
• Common in children.
• This mode of infection occurs from anus to mouth

Question 14

Retro infection in E. vermicularis

Answer 14

• The eggs laid on the perianal skin immediately hatch into the infective stage larva and migrate through the anus to develop into worms in the colon
• This mode of infection occurs from anus to colon

Question 15

Pathogenecity of E.vermicularis

Answer 15

• Crawling of the gravid female worm leads to perineal pruritus (pruritis ani).
• As the worm migrates out at night, it disturbs sleep.
• Nocturnal enuresis is sometimes seen.
• The worm crawling into the vulva and vagina causes irritation and a mucoid discharge.
• It may migrate up to the uterus, fallopian tubes and into the peritoneum. This may cause symptoms of chronic salpingitis, cervicitis, peritiontis and recurrent urinary tract infections.
• The worm is sometimes found in surgically removed appendix and may be responsible for some cases of appendicitis

Question 16

Laboratory diagnosis of E.vermicularis

Answer 16

• Pinworm infestation can be suspected from the history of perianal pruritus
  1. Stool examination
  2. Perianal swabs

Question 17

How stool examination is done for E.vermicularis ?

Answer 17

• Stool examination is not useful in diagnosis

* The adult worms may sometimes be noticed on the surface of stools

Question 18

Explain the Perianal swabs procedure?

Answer 18

• Collected early morning, before going to the toilet or bathing are most often positive.
• Scotch (cellophane) Tape Method:

1. Adhesive transparent cellophane tape held sticky side out, on a wooden tongue depressor.
2. The mounted tape is firmly pressed against the anal margin, covering all sides.
3. The tape is transferred to a glass slide, sticky side down, with a drop of toluene for clearing and examined under the microscope.

• Eggs and female adults can be detected.

Question 19

Adult worm morphology in Trichuris trichiura

Answer 19

• The male worm is 30–45 mm long, while the female is slightly larger, about 40–50 mm
• The worm is flesh-colored
• It resembles a whip, with the anterior three fifth thread-like thin and the posterior two fifth fleshy thick like the handle of a whip
• The posterior end of the male is coiled ventrally, while of the female is straight

Question 20

Structure of Egg in Trichuris trichiura

Answer 20

• It is brown in color being bile-stained
• It is barrel-shaped and about 50 μm long and 25 μm wide in the middle, with a projecting mucus plug at each pole.
• The plugs are colorless
• It contains an unsegmented ovum
• At this stage, it is not infective for humans

Question 21

Habitat of T.trichiura

Answer 21

Large intestine

Question 22

Common name for T.trichiura

Answer 22

Whipworm

Question 23

Who is the natural hoat in Trichuris trichiura ?

Answer 23

Human

Question 24

Invective form of T.trichiura

Answer 24

Embryonated eggs contaning Rhabditiform larva

Question 25

Life cycle of Trichuris trichiura

Answer 25

• Adult female worm lives in large intestine with the thread-like anterior portion piercing the mucosa and the thick posterior end projecting out
• Eggs which are discharged in feces
• The egg undergoes development in soil, then infective rhabditiform larva develops within the egg “embryonated eggs” which are now infective to man
• Mode of Transmission: Ingestion of infective stage “embryonated eggs” in contaminated food or water
• The eggs hatch in the small intestine and the larva and pass down to the caecum to become mature adults

Question 26

Pathogenicity of T. trichiura

Answer 26

• Infection with T. trichiura is asymptomatic, except when the worm load is heavy
• Mucus diarrhea, chronic dysentery and abdominal pain, and weight loss are frequently seen in such cases
• Microcytic anemia even though the worm is not a blood feeder, oozing of blood may occur at the sites of attachment
• Acute appendicitis from the mechanical blockage of the appendix lumen by masses of whipworms
• Rectal prolapse in some patients, particularly young children

Question 27

Laboratory diagnosis of T. trichiura

Answer 27

1. Stool Examination
   * The characteristic barrel-shaped eggs are found in stools.
2. Sigmoidoscopy
   * In heavy infection, white worms hanging from inflamed mucosa “coconut cake rectum”