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Term Paper on Ancylostoma Duodenale (Hookworm)
Term Paper Contents:
- Term Paper on the Geographical Distribution of Ancylostoma Duodenale
- Term Paper on the Habits and Habitat of Ancylostoma Duodenale
- Term Paper on the Morphology of Ancylostoma Duodenale
- Term Paper on the Digestive System of Ancylostoma Duodenale
- Term Paper on the Excretory System and Nervous System of Ancylostoma Duodenale
- Term Paper on the Reproductive System in Ancylostoma Duodenale
- Term Paper on the Life History of Ancylostoma Duodenale
- Term Paper on the Diagnosis and Pathogenesis of Ancylostoma Duodenale
- Term Paper on the Treatment and Prevention of Ancylostoma Duodenale
Term Paper # 1. Geographical Distribution of Ancylostoma Duodenale:
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Ancylostoma, the common hookworm of man, was first discovered in 1838 by an Italian physician Dubini. The pathogenesis and mode of entrance of the larvae into man was worked out by Looss in 1898. However, Ancylostoma doudenale or Old World hookworm parasitizes the intestine of man. Another related genus Necator americanus, the American hookworm or the New World hookworm is most common in Sri Lanka and India.
About one-half billion people or nearly 25% of the world population are infected by the hookworms. Ancylostoma duodenale, commonly known as the “old world hookworm”, is the common hookworm of man in tropical, subtropical and temperate regions of Asia, Africa, Europe, Pacific Islands and South America. However, the incidence is greater in Europe and Asia. Some other species of Ancylostoma, namely A. caninum and A. braziliense, both in dogs and cats, and A. malayanum in bears, are also common.
Term Paper # 2. Habits and Habitat of Ancylostoma Duodenale:
The adult worms of Ancylostoma duodenale are endoparasites and live in the intestine of man particularly in the jejunum, less often in the duodenum and rarely in the ileum. The infective juveniles find their way in the human host percutaneously from the soil contaminated by the faeces in which they live. Hookworms flourish under primitive conditions where people move barefoot, modern sanitary conditions do not exist and human faeces are deposited in the ground.
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Term Paper # 3. Morphology of Ancylostoma Duodenale:
Shape, Size and Colour:
Ancylostoma duodenale is cylindrical in form and white or grey in colour. The male is about 8 to 11 mm long and the female is 10 to 13 mm long.
Structure:
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The anterior end of male and female are similar. It is bent dorsally and has a large buccal capsule. It possesses two ventro-lateral cutting plates, each bears two large teeth, and a dorsal cutting plate. The dorsal cutting plate bears two small teeth and a deep median cleft which encloses the dorsal gland. Deep in the buccal capsule is present a pair of saw-like internal teeth. Ducts of cephalic glands open on the ventro-lateral sides of the capsule. Their secretion dissolves the intestinal mucosa of the host.
At the posterior end of male is present an umbrella-like copulatory bursa supported by fleshy bursal rays. The bursa surrounds the cloaca. The posterior end of female terminates in a caudal spine. In female the gonopore and anus are separate, while in male gonopore and anus open in the cloaca.
The body of Ancylostoma is covered externally by cuticle, it is followed internally by the epidermis and musculature which is directed longitudinally. Its body cavity is the pseudocoel surrounding the various organs systems.
Copulatory Bursa:
The posterior end of female is somewhat tapes, bluntly rounded in the form of a cone and terminates into a minute spine. The posterior end of male is broad and with an umbrella like structure called bursa. The bursa is supported by fleshy bursal rays of definite arrangement.
Musculature:
The somatic muscles consist of a single layer of cells underlying a hypodermis and arranged into four longitudinal groups. These four groups are interrupted by four longitudinal quadratal chords located on the dorsoventral and lateral axes. Because muscle cells are limited to two in each sectioned quadrant the worms are called meromyarial. They almost complete lack of transverse muscle cells.
Term Paper # 4. Digestive System of Ancylostoma Duodenale:
It is tubular and very simple. It consists of the mouth, buccal capsule, muscular pharynx having a triradiate lumen lined by cuticle, oesophageal bulb, intestine, rectum and cloaca in male but an anus in female. There are five glands connected with the digestive system; one of them, called the oesophageal gland, secretes a ferment which prevents the clotting of blood so that the worm can suck blood from the host.
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In fact, its food consists of intestinal mucous membrane and blood. In the process the tiny teeth and cutting plates of the buccal capsule make small wounds in the intestinal mucosa through which the food and body fluid is sucked by the suctorial action of the pharynx. After feeding it leaves a bleeding wound and moves to another location. An adult worm is said to suck nearly 0.8 ml of blood in a day from the host causing severe anaemia. Digestion is, however, completed in the intestine.
Term Paper # 5. Excretory System and Nervous System of Ancylostoma Duodenale:
Excretory System:
The excretory system is rather complicated. Flame cells are absent in nematodes. The excretory system consists of two excretory canals embedded in the lateral chords and an isthmus in the pharyngeal region. Surrounding or adjacent to the isthmus, are other excretory structures including an excretory sinus into which tributaries from the lateral canals open and from which ventrally is given off a short, cuticulae, terminal duct.
The duct opens at a ventral excretory pore. From the excretory sinus two large, sub-ventral glands of uncertain function arise posteriorly. The tributary canals emerge from sub-ventral glands and penetrate the lateral chords where they join the lateral canal. These lateral canals extend from the region of buccal capsule to the posterior end of the body where they end blindly.
Nervous System:
Encircling the pharynx, in front of the excretory pore, is a nerve ring. From a large ganglion located on the ventral portion of the nerve ring, a large nerve runs in the ventral chords to the posterior end, and smaller nerves run in the lateral chords anteriorly and posteriorly. Four small nerves run forward from the ring to supply anterior end. These main nerve trunks are connected in a complicated Fashion by nerve commissures.
Term Paper # 6. Reproductive System in Ancylostoma Duodenale:
The sexes are separate and sexual dimorphism is well distinct.
1. Male Reproductive Organs:
The male reproductive organs comprise a single, tubular, thread-like testis twisted around the intestine in the middle of the body. Testis continues posteriorly in a vas deferens which finally opens into an elongated, swollen, saclike seminal vesicle. The seminal vesicle soon tapers to form a narrow passage called the ejaculatory duct which opens into the cloaca.
2. Female Reproductive Organs:
The female reproductive organs comprise two much highly twisted tubules, the ovaries. One ovarian tubule is placed anteriorly and other posteriorly from a little behind the middle of the body. Both the ovarian tubules continue into the oviducts and, thus, the two oviducts open into elongated and dilated seminal receptacles, each continues into muscular uterus.
Thus, the two uteri (one from anterior and other from posterior) meet a little behind the middle of the body of form a short tubular vagina which opens out by vulva or the gonopore situated at the junction of the posterior and middle third of the body.
Term Paper # 7. Life History of Ancylostoma Duodenale:
The life history of Ancylostoma duodenale is monogenetic as no intermediate host is required; man is the only main host for ancylostoma duodenale.
Copulation:
It occurs in the host intestine. The copulatory bursa of male enters the female gonopore and thus, sperms are transferred into the vagina of female.
Fertilization:
The female produces thousands of eggs per day. Fertilization of eggs takes place in the uterus. The fertilized egg passes out with the host faeces.
Eggs:
The eggs are oval or elliptical in shape measuring 65µm in length by 40µm in breadth, colourless and protected by a transparent hyaline shell-membrane. An egg that comes out of the host body possesses an embryo up to 4-celled or 8- celled stage. The eggs, which passed out with the faeces are not infective to man.
The female worm lays eggs in the intestine of the host which pass out with faeces. On an average nearly 9,000 eggs are laid per day by a female.
Larval Development:
Under favourable environmental conditions of moisture, oxygen supply and temperature (58- 85°F), the embryo develops into the first stage juvenile of rhabditiform larva which hatches out within 24 to 48 hours.
The newly hatched larva has a mouth a buccal capsule, an elongated pharynx with an oesophageal bulb and an intestine. It feeds on the bacteria of the faeces or other organic debris of the soil for 4 to 5 days and moults twice to form a third stage juvenile or the filariform larva. This juvenile is about 0.5 mm long and infective for man. It has a non-patent mouth and therefore does not feed. But, it may remain alive and infective for several weeks under favourable conditions.
Infection of a New Host:
The filariform larva infects a new host (man) by chance contact with the skin. Its anterior end is equipped with oral spears which enable the larva to penetrate the skin of a potential human host. The larvae may bore through the skin in any part of the body.
Most generally they penetrate the soft skin on the sides of the feet and hands, through hair follicles. Their penetration is generally accompanied by a serve dermatitis called “ground itch”, characterized by ulceration of skin about wounds. Besides percutaneous entrance, infection is also possible through ingestion of contaminated food and water.
Migration and Later Development:
On reaching the subcutaneous tissues the larvae enter into the lymphatics and small venules. They pass through the lymphatic-vascular system into the venous circulation and are carried through the right heart into the pulmonary capillaries, where they break through the capillary walls to enter into the alveolar space.
They then migrate on the bronchi → trachea → larynx, and crawl over the epiglottis to the back of the pharynx and are finally swallowed. During its migration, when it reaches to oesophagus, its third moulting occurs and a terminal buccal capsule is formed. The time taken in this migration is about 10 days.
Thus, finally the growing larvae settle down in the small intestine and undergo fourth and finally moult to become the adults. In about 3 to 4 weeks’ time they become sexually mature to repeat the life history again.
Term Paper # 8. Diagnosis and Pathogenesis of Ancylostoma Duodenale:
Diagnosis:
Hookworm infection is diagnosed by the observation of the hyaline “eggs” in a faecal smear from the infected person.
Pathogenesis:
Pathogenicity is fairly extensive involving skin, lungs and small intestine. The penetrating larvae cause characteristic tiny and irritating sores, called dew sores or ground itching, and inflammation of skin. In lungs, the migratory larvae cause petechial haemorrhages and bronchial pneumonites.
But the greatest damage occurs in the small intestine by the adult worms. Here, the punctured wounds continue to bleed for some time so that more blood is lost than the worms can consume. This result in severe anaemia, decrease in general immunity and bloody stools. Intestinal wounds may lead to various forms of detrimental infections.
Deleterious toxins secreted by glands in the head region of worms cause stomach pain, food fermentation, diarrhoea, constipation, dyspnea, palpitation of heart, eosinophilia, loss of health and collapse. Mental and physical growth is retarded in children and growing youth. The patient tries to ease the epigastric pain by eating, even dirt, hence the term “dirt eaters”. Unchecked infection may lead to fatty degeneration of the heart, liver and kidneys, ending in death.
Term Paper # 9. Treatment and Prevention of Ancylostoma Duodenale:
Treatment:
Drugs like carbon tetrachloride, thymol, oil of chenopodium, hexylresorcinol, etc., are used effectively to control the infection of Ancylostoma. Some other anti-helminth drugs like tetrachloroethylene and blephenium are found to be more effective and are safe to be used.
Prevention:
The hookworm disease is responsible for considerable economic loss as well as poor health. Important prophylactic or preventive measures include wearing shoes and sanitary disposal of human faeces in affected areas so that soil may not be polluted.