In this article we will discuss about Ancylostoma Duodenale:- 1. Habit and Habitat of Ancylostoma Duodenale 2. Geographical Distribution of Ancylostoma Duodenale 3. Structure 4. Digestive System 5. Reproductive Organs 6. Life Cycle 7. Diagnosis, Disease and Pathogenicity 8. Treatment and Prevention.
Contents:
- Habit and Habitat of Ancylostoma Duodenale
- Geographical Distribution of Ancylostoma Duodenale
- Structure of Ancylostoma Duodenale
- Digestive System of Ancylostoma Duodenale
- Reproductive Organs of Ancylostoma Duodenale
- Life Cycle of Ancylostoma Duodenale
- Diagnosis, Disease and Pathogenicity of Ancylostoma Duodenale
- Treatment and Prevention of Infection Caused by Ancylostoma Duodenale
1. Habit 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.
2. Geographical Distribution of Ancylostoma Duodenale:
Ancylostoma duodenale is widely distributed in all tropical and subtropical countries, occurring in places wherever humidity and temperature are favourable for the development of larvae in the soil.
It is found in Europe, North Africa (especially prevalent in Egypt), India (Punjab and Uttar Pradesh), Sri Lanka, Central and North China, Pacific Islands and Southern States of America. About one-half billion people or nearly 25 per cent of the world population are infected by the hookworm.
3. Structure of Ancylostoma Duodenale:
(i) Shape, Size and Colour:
Adult Ancylostoma duodenale are small and cylindrical in shape. Sexes are separate; the male is about 8 mm in length and 0.4 mm in diameter, while female is generally longer about 12.5 mm in length and 0.6 mm in diameter. When freshly passed, it has a reddish brown colour due to ingested blood in its intestinal tract.
(ii) External and Internal Structures:
The anterior end of the worms of both sexes is slightly bent dorsally (hence, the name hookworm) and has a large buccal capsule. The large and conspicuous buccal capsule is lined with a hard substance and is provided with 6 cutting plates or teeth, 4 hook-like on the ventral surface and 2 knob-like (triangular plates) or sharp lancets on the dorsal surface.
The buccal capsule helps in attachment with the intestinal wall of the host. The posterior end of female worm tapers bluntly in a short post-anal tail, while that of the male is expanded an umbrella-like. This expanded structure is called copulatory bursa which surrounds the cloaca.
The copulatory bursa has two lateral lobes with six muscular rays in each, and a small median dorsal lobe with one main dorsal ray which is divided only at the tip.
The arrangement of rays is remarkably constant and each ray is given a name, the main ray in the dorsal lobe is called a dorsal ray, in each lateral lobe beginning from the dorsal side the six rays are called externo-dorsal, postero-lateral, medio-lateral, externo-lateral, latero-ventral, ventro-ventral. The teeth in the buccal capsule and bursal rays are of taxonomic importance.
The body of Ancylostoma duodenale 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 organ systems.
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.
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. The mode of respiration, excretory system, nervous system and receptors are like those of Ascaris lumbricoides.
5. Reproductive Organs of Ancylostoma Duodenale:
Sexes are separate and sexual dimorphism is well distinct.
However, 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, sac-like seminal vesicle. The seminal vesicle soon tapers to form a narrow passage called the ejaculatory duct which opens into the cloaca.
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 to 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.
6. 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 and Fertilization:
Copulation occurs in the intestine of the host, during the process the copulatory bursa of male is applied on the vulva of female and sperms are transferred.
In fact, during copulation the worms (a male and a female) assume a Y-shaped figure owing to the position of the genital openings. The sperms, thus, transferred come to lie in the seminal receptacles where fertilisation takes places. The fertilised eggs are then pushed into the uteri for laying through vagina and gonopore.
Egg Laying:
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.
Eggs:
The eggs are oval or elliptical in shape measuring 65 pm in length by 40 pm 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.
Development in Soil:
Under favourable conditions of environment like moisture, oxygen and temperature (about 68-85°F), the embryo develops into a rhabditiform larva or first stage juvenile; it is about 250 µm in length. This larva hatches out of the egg in the soil in about 48 hours. This larva possesses the mouth, buccal capsule, elongated pharynx, bulb-like oesophagus and intestine.
It feeds on bacteria and other debris of the soil and moults twice, on the third day and the fifth day. It then develops into a filariform larva measuring about 500 to 600 pm in length. It is the infective stage of the parasite. This larva does not feed but remains infective and alive for several weeks under favourable conditions. The time taken for development from eggs to filiform larvae, is on an average 8 to 10 days.
Infection to New Host:
The filiform larvae are infective to man. The larvae cast off their sheaths and penetrate the skin of a human host. The anterior end of the larva is provided with oral spears by which it penetrates the soft skin of the feet and hands, generally through hair follicles.
Migration and Later Development:
On reaching the subcutaneous tissues, the larvae enter into the lymphatic’s 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 spaces.
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 final moult to become the adults. In about 3 to 4 weeks time they become sexually mature to repeat the life history again. The life span of the adult worm in human intestine has been estimated differently by different workers; generally it is believed to be 3 to 4 years.
7. Diagnosis, Disease and Pathogenicity of Ancylostoma Duodenale:
The infection of hookworm is easily diagnosed by the presence of its eggs in faecal smear from the patient. The disease caused by its infection is generally referred to as ancylostomiasis.
Pathogenicity of Ancylostoma Duodenale:
The hookworms are the most dangerous parasitic nematodes because they hold on to the intestinal villi and suck blood and body fluids of the host by their muscular pharynx, they also cut holes in the intestinal mucosa and leave bleeding wounds. It causes severe anaemia. In children, where incidence of infection is very great, they retard the physical and mental growth.
Some toxins secreted by the glands in the head region of worms cause stomachache, food fermentation, diarrhoea, constipation, dyspnea, palpitation of heart, eosinophilia, ill health and the patient may finally collapse.
During penetration of larvae in the skin, local irritation is caused resulting into inflammation of the surrounding tissues; these may result into tiny sores. The migratory larvae in lungs may cause haemorrhage and bronchial pneumonites.
8. Treatment and Prevention of Infection Caused by Ancylostoma Duodenale:
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 of Infection by Ancylostoma Duodenale:
The infection of Ancylostoma duodenale can be checked effectively by improving the sanitary conditions to avoid the contamination of faeces with the soil and other edibles, by protecting feet and hands from being touched with the soil. Children should be directed to keep their hands and nails clean.