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Ancylostoma duodenale1
1. Ancylostoma duodenale
Introduction
Common name: The old world hookworm. The parasite was first discovered in 1838 by
an Italian physician Angelo Dubini.
Geographical distribution:
It is widely distributed in all tropical and sub-tropical countries.
It is found in Europe, North Africa, India (Punjab and U.P).
Habitat: The adult worm lives in the small intestine of man, particularly in the jejunum.
Morphology:
Adult
It is small, greyish white, cylindrical worm.
It appears reddish brown when freshly passed in faeces due to ingested blood in its
intestinal tract.
The anterior end of the worm is bent slightly dorsally, hence the name hookworm.
The buccal cavity is armed with two pairs of teeth and two knob like plates.
It has both digestive and excretory system.
There are 5 glands connected with the digestive system, one of them called an
oesophageal gland, secretes a ferment which prevents the clotting of blood from the site
of bite.
Male
Size: Smaller, 8mm in length.
Shape of tail: Expanded in an umbrella like fashion (copulatory bursa).
Genital opening: Posteriorly opens with cloaca.
Female
Size: Longer than male, 12.5mm in length.
Shape of tail: Tapering, no expanded bursa.
Genital opening: middle third of the body.
Eggs
Oval or elliptical in shape measuring 65x40um.
Colourless.
Surrounded by a transparent hyaline shell membrane.
Contains a segmented ovum usually with 4 blastomeres ; has a clear space between the
egg shell and segmented ovum.
Floats in saturated solution of common salt.
The eggs when passed out in faeces, are not infective to man.
3. Life Cycle
No intermediate host is required. Man is only the definitive host for A. duodenale.
The various stages of life cycle are as follows:
Stage I: Passage of eggs from infected host:
The eggs containing segmented ova with 4 blastomeres, are passed out in the
faeces of the human host.
Stage II: Development in soil:
From each egg a Rhabditiform larva (250um in length) hatches out in the soil in about 48
hours.
The Rhabditiform larva moults twice (3rd and 5th day)
Later it then develops into a filariform larva (500- 600um) in length, the infective stage
of the parasite.
The time taken for development from egg to filariform larvae is 8-10 days.
Stage III: Entrance into a new host:
The filariform larva are infective to man. The larvae gain entrance to the body by
penetrating the skin.
Stage IV: Migration:
The larvae penetrate the skin and enter into the lymphatics or small venules.
It is then carried to the heart and lungs.
In the lungs, it breaks the capillaries and enters the alveoli.
They then migrate on to the bronchi, trachea and larynx, crawl over the epiglottis to the
back of the pharynx and are ultimately swallowed.
On entering the oesophagus, a 3rd moulting takes place and a terminal
buccal capsule is formed.
Stage V: Localisation and Laying of eggs:
The larvae settle down in the small intestine .
The larvae with the help of buccal capsule, attach to the intestinal mucosa and grows into
an adult worm.
In about a months they are sexually mature and eggs are laid by the female. The eggs are
passed in stool and then the cycle is repeated.
4. Pathogenicity and Clinical features
The worm causes hookworm disease or ancylostomiasis in man.
Mode of infection:
This occurs when man walks bare foot on the faecally contaminated soil.
The filariform larvae penetrate directly through the skin with which they come in contact.
The most common sites of their entry are
the thin skin between the toes.
the dorsum of the feet.
the inner side of the soles.
The larvae can penetrate any part of the skin which is sufficiently thin.
Infection may also occur by the accidental drinking of water contaminated with filariform
larvae.
Infecting agent: Filariform larvae
Migration: through lungs.
Portal of entry: skin
Site of localisation : small intestine.
5. Pathogenic effects: These may be considered
under two heads.
1. Pathogenic effect caused by Ancylostoma larvae.
2. Pathogenic effect caused by Adult worms.
Pathogenic effect caused by Ancylostoma larvae.
Lesions in the skin:
i) Ancylostome dermatitis(ground itch)
ii) Creeping eruption.
Ground itch: occurs at the site of entry disappears in 1-2 weeks.
Creeping eruption:
It is a condition in which filariform larvae wander about through the skin for several
weeks and months (upto 2 yrs) producing a reddish itchy papule.
Lesions in the lungs:
Bronchitis and bronchopneumonia may occur when the larvae break through the
pulmonary capillaries and enter alveolar space
marked eosinophilia occurs at this stage.
Pathogenic effect caused by adult worms:
The adult worm inhabit the small intestine (jejunum of man , attaching
themselves to the mucous membrane by means of their powerful buccal.
Anemia of microcytic hypochromic type develops.
Causes of anemia:
i) chronic blood loss: A duodenalae sucks about 260ul ( 0.2ml ) blood per day, but a
greater amount of blood is lost by bleeding from the site of bite. It is facilitiated by an
anticoagulant like substance secreted by the oesophageal gland.
ii) Nutritional defects: deficiency of the available iron and haemopoietic substances in
the diet. - with iron deficiency a microcytic hypochromic anemia.
- with deficiency of folic acid and vitB12 a macrocytic type of anemia.
Clinical features:
This may be considered under two heads;
Gestrointestinal manifestation:
duodenal ulcer
abnormal appetite
hypoacidity
Achlorhydria
Effects of Anaemia:
The skin assumes a swallow appearance (light yellow color).
The mucous membrane of the eye, lips and tongue show extreme pallor (lack of color).
6. Prevention
Prevention of soil pollution by proper control of sewage disposal.
Personal protection – wearing of boots and gloves.
