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Hookworm Infection (Ancylostomiasis): Morphology, Life Cycle And Clinical Presentations

Updated on April 1, 2014

Diagrammatic Representation Of Hookworms And Whipworms



Hookworm infection is prevalent in hot damp areas throughout the tropics and subtropics. Two species of hookworms- Ancylostoma duodenale and Necator americanus are seen to parasitize the small intestine of man. Ancylostoma is more harmful than Necator because it is more persistent in the environment and causes heavier blood loss. Ancylostoma is seen in the tropical and temperate zones whereas Necator is more widespread in the tropics.

In the rural communities in Africa, the prevalence for hookworm in adults ranges from 15 to 40%. In children with increasing age, the prevalence rates also increase being 2% at 1 year of age to 10% in the 12th year. In 60 to 70% of affected persons, Ascaris lumbricoids and Trichuris trichura may also be present. In almost all parts of India, Far east, Africa and South America, both types of hookworms are seen. In South India, N. americanus predominates.

Morphology And habitat: Man is the natural host. The adults remain in the small intestine. Eggs are passed in feces.

Adult worm of Ancylosioma duedenale is 8 to 13 mm long and is thread-like in thickness. The buccal cavity has four pointed hooklike teeth. Necator americanus is smaller than A. duodenale. The buccal cavity contains two chitinous cutting plates. The worms attach to the intestinal villi of the jejunum and duodenum by their mouth parts. They produce bleeding points from which the blood passes through the alimentary canal of the worm continuously. This blood is required for the nutritive and respiratory functions of the worm.

The loss of blood caused by a single ancylostome is estimated to be 0.1 to 0.2 ml/day. Necator causes a blood loss of 0.01 to 0.03ml. The fertilized female lays about 20,000 eggs a day. The eggs measure 40 to 60u and are embryonated when passed. Necator americanus lays fewer eggs than A. duodenale. The eggs are larger (60 to 70u).

Rarely, two other specieis of hookworms- A.cyclonicum and A. braciliense- may affect man. Ancylostoma cyclonicum is a hookworm of cat found in the far east, which occasionally reaches maturity in humans. Ancylostoma braxiliensis is a hookworm of dogs and cats which may also infect but does not reach maturity.

The Hookworm Foot Manifestation


The Life Cycle Of Hookworms

Eggs are passed in feces and in 5 days, they hatch in warm moist soil. The rhabditiform larvae come out and they moult twice on the third and fifth days and develop into filariform larvae which develop a sheath. These are infective to man. The larvae can persist in the soil for two months, feeding on bacteria and other organic matter. On coming into contact with the skin of man, the sheath is shed and the larvae penetrate into the subcutaneous tissues and enter the lymphatics and venules.

Within three days of entry into the skin, the larvae pass through the right side of the heart and the pulmonary capillaries to enter alveolar spaces. Foci of inflammation develop in the lungs. Then they enter the bronchi and pass up the trachea, larynx and back of the pharynx to be swallowed. In the esophagus, a third moulting occurs and a terminal buccal capsule is formed. In the small intestine, they attach to the villi and grow into adults in 3 to 5 weeks. Average lifespan of the worm is 2 years, but sometimes it may exceed 10 years.

Hookworm Infection On The Foot


Clinical Manifestations Of Ancylostomiasis

Skin: The site of entry of the larvae becomes itchy and sudden. It ulcerates and becomes secondarily infected (ground itch). Common site for this lesion is the web of the toes. Larval migration through the lungs may lead to allergic symptoms, malaise, eosinophilia, dyspnea, cough and hemoptysis.

Intestinal tract: Mild infections are usually asymptomatic. When the worm load is heavy, considerable blood loss occurs from the intestine. This leads to iron deficiency anemia which is aggravated by coexistent malnutrition. Vague abdominal symptoms like pain resembling peptic ulcer or chronic intestinal amoebiasis may develop.

Heavy infection also leads to severe anemia, stunted growth, apathy, reduction of learning abilities in children, frequent absence from work and school, diminished productivity, impairment of immune responses, frequent respiratory infections and increased susceptibility to tuberculosis.

© 2014 Funom Theophilus Makama


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