Ancylostoma Duonale, Necator Americanus and Enterobius Vermicularis

The Hookworms

Hookworms are parasitic round worms that lives in the small intestine of its host, which may be a mammal such as a dog, cat, or human.

Two species of hookworms which are pathogenic to human are

Ancylostoma duodenale

Necator americanus

Ancylostoma duodenale

Are small grayish white or pink with the head slightly bent in relation to the rest of the body.

This curvature forms a definitive hook shape at the anterior end for which hookworms are named.

They possess well developed mouths with two pairs of ventral teeth.

Males measure approximately 1cm by 0.5 mm the females are often longer and stouter.

Additionally, males can be distinguished from females based on the presence of a prominent posterior copulatory bursa.

Is very similar in morphology to Ancylostoma duodenale.

Is generally smaller than Ancylostoma duodenale with males usually 5 to 9 mm long and females about 1 cm long.

Possesses a pair of semi lunar cutting plates in the buccal capsule.

Additionally, the hook shape is much more defined in Necator than in Ancylostoma

The eggs are oval or elliptical, measuring 60 μm by 40 μm, colorless, not bile stained with a single thin transparent hyaline shell membrane.

When released by the worm in the intestine, the egg contains an unsegmented ovum.

During its passage down the intestine, the ovum develops.

As the eggs of both Ancylostoma and Necator (and most other hookworm species) are indistinguishable, to identify the genus, they must be cultured in the lab to allow larvae to hatch out.

Mouth parts (teeth)

of Ancylostoma

duodenale

Mouth parts

(cutting plates) of

Necator

americanus

Rhabditiform larva of hookworm

Hookworm ova

Through skin penetration of infective filariform larvae (third stage larvae or L3) contained in the soil. In addition, infection by A. duodenale may probably also occur by the oral route.

Eggs are passed in the stool and under favorable conditions (moisture, warmth, shade), larvae hatch in 1 to 2 days.

The released rhabditiform larvae grow in the faeces or the soil.

The rhabditiform larvae are active and feed on dead organic matter in the soil.

After 5 to 10 days (after two molts) they become filariform (third-stage) larvae that are infective. The filariform larvae are not active and do not feed, They can survive 3 to 4 weeks in favorable environmental conditions in the soil.

Upon contact with the human host, the larvae penetrate the skin, invade the blood capillaries and are carried through the blood vessels to the heart and then to the lungs.

They break from the blood capillaries and appear into the pulmonary alveoli, ascend the inverted bronchial tree to the pharynx, and are swallowed.

The larvae reach the small intestine, where they reside and mature into adults. Adult worms live in the lumen of the small intestine, where they attach to the intestinal wall.

The life span of adult worms in the small intestines is about 1 to 2 years.

Diseases Caused

Ground itch at the time of skin penetration: irritating vesicular rash limited to the site of invasion, usually in the sole of feet or hands.

Both species causes ancylostomiasis and necatoriasis respectively

Severe anemia

Stunted growth

Malnutrition and general body debility

Diagnosis

Specimen

Stool

Microscopy

Wet mount and concentration technique to detect ova.

Culture

(Kato Katz technique) for recovery of rhabditiform larvae (but not routine)

Drug of choice

Albendazole

Mebendazole

Pyrantel pamoate

Female

They are small, 9-12 mm x 0.4 mm

Has a cervical alae (wing like expansion) at the anterior end

There is a buccal cavity that terminates into a prominent oesophageal bulb

Has a long-pointed tail

Male

2-5 mm with a curved tail and a single spicule

Males are seldom seen

Egg

50-54 x 20-27 μm with characteristic shape – flattened on one side. Almost colourless with bean-shaped double contour shell

Eggs of Enterobius vermicularis in wet mount

Eggs of Enterobius vermicularis in cellulose preparation

Ingestion of eggs from contaminated fingers, bedding and formites

Inhalation of eggs from dust

Autoinfection

Retroinfection

Eggs are deposited on perianal area. Self-infection occurs by transferring infective eggs to the mouth with hands that have scratched the perianal area (Autoinfection).

The ingested eggs hatch in the small intestine to produce larva.

The larva matures and become adult in the large intestine where the male fertilizes the female.

The female migrates to the perianal folds where deposit eggs on perianal skin fold.

These would be swallowed and follow the same development

Sometimes eggs hatch at the perianal area and the larva migrates to the caecum where they mature to become adults and fertilization takes place (Retro infection)

Under optimal conditions, it takes 4 to 6 hours for the eggs become infective.

The time interval from ingestion of infective eggs to oviposition by the adult females is about one month.

The life span of the adults is about two months.

Disease they Cause

Pruritus ani is the main symptom and varies from mild itching to acute pain which occurs mainly at night.

The pruritus provides scratching of the perianal region resulting in excoriation and secondary infection.

Vulvitis may be caused by pinworms entering the vulva causing a mucoid discharge and pruritus vulvae.

Specimen

Scotch tape swab

Stool

Technique

Microscopy

Wet mount and concentration technique to detect ova

Examination of the tape swab for ova

Drugs of Choice

Albendazole

Mebendazole

Hookworm and Enterobius vermicularis are intestinal small round worms

Hookworm follows heart lung migration in its life cycle while Enterobius vermicularis follows direct life cycle without heart lung migration.

Hookworm is transmitted through skin penetration by filariform larvae in the soil

Enterobius vermicluaris is transmitted through

Ingestion of eggs from contaminated fingers, bedding, and formites

Autoinfection

Retroinfection

What is the mode of transmission of hookworm?

Mention the most common complication of hookworm infection.

Mention drugs of choice for enterobiasis and hookworms.