• Hookworms are parasitic nematode that lives in the small intestine of mammalian host such as dog, cat or humans.
• They are characterized by their presence of well-defined buccal capsules bearing clotting plates and teeth.
• Two species of hookworms, commonly infect humans:
  • Ancylostoma duodenale
  • Necator americanus
• Ancylostoma duodenale, also known as the old hookworm is a common hookworm of human.
•  It causes ancylostomiasis in humans, characterized by non-deficiency anemia and hypoalbuminemia.
• Necator americanus also known as the New World hookworm is another cause of hookworm disease in humans.
•  Necatoriasis is the term for the condition of being host to an infestation of a species of Necator.

Habitat:

• The adult worm lives in the small intestine of a man particularly in the jejunum, less often in the duodenum and rarely in the ileum.

Morphology: Ancyclostoma duodenale

Adult worm:

• It is small greyish white, cylindrical worm.
• When freshly passed the worm has a reddish-brown color due to the ingested blood in intestinal tract.
• The anterior end of the worm is bent slightly in the same direction of the body curve resembling a hook, hence they are called hookworms.
• The large and conspicuous buccal capsule is lined with a hard substance
• The buccal capsule is provided with 6 teeth, 4-hook like on the ventral surface and had a pair of knob-like (triangular plates) on the dorsal surface.
• There are five glands connected with the digestive system:
  • one of them called the esophageal gland, secretes a ferment which prevents the clotting of blood.
• The sexes are easily differentiated by their size, the shape of the tail and position of the genital opening.
• Male:
  • shorter, measuring 8mm in length, the posterior end is expanded in an umbrella like fashion (copulatory bursa).
  • -Genital opening is present posteriorly and opens with the cloaca.
• Female:
  • longer than males, measuring 12.5 mm in length.
  • The posterior end is tapering and possess no bursa.
  • The genital pore is present at the junction of posterior and middle third of the body.
  • Owing to the position of the genital opening, the worm assumes the Y-shaped figure during copulation.
• Copulatory bursa in males is characteristic bell shaped used to catch and hold the female nematode during mating.
• – It is membranous, asymmetrical and consists of 13 fingers like rays in 3 lobes: 1 dorsal and 2 lateral.
• -Dorsal lobe consists 3 (1 single dorsal ray and 2 external dorsal rays: the two lateral lobes contain 1/3 pairs of lateral rays and 2 pairs of ventral rays).

Eggs:

• Eggs are oval in shape.
• 60 mm in length and 40 mm in breadth colorless.
• They are surrounded by a transparent hyaline shell-membrane.
• Eggs contain an un-segmented ovum usually with 4 blastomeres.
• A clear space is present between the egg shell and segmented ovum.
• These eggs floats in saturated solution of common salt.
• The eggs of Necator is slightly smaller than Ancylostoma.
• The female Ancylostoma produces 10,000-20,000 eggs per day whereas N. americanus produce less eggs i.e. 3000-6000 per day.

Filariform larva:

• It is the non-feeding form of the worm and is the infective form of the parasite.

Life cycle:

• The life cycle of the two species of hook worm are same.
• The only difference is the morphology of filariform larva.
• Life cycle is completed in a single host, the man. No other intermediate host is required.
• The following are the various stages of the life cycle:
• Stage 1: Passage of eggs from the infected host
  • The eggs containing segmented oval with 4 blastomeres, are passed out in the feces of human host.
• Stage 2: Development in soil
  • Eggs under the favorable conditions (damp, warm, well-oxygenated soil) hatch to rhabditiform larva (250mm in length) i.e. L1 larva within 48 hours.
  • The rhabditiform larva moults twice, on the 3^rd and 5^th day to develop into a filariform larva (500—600 mm in length), the infective stage of the parasite.
  • The time taken for development from eggs to filariform larva is on an average 8-10 days.
• Stage 3: Entrance to new host
  • The L3 larva cast of their sheath and gain entrance into the body by penetrating the skin, through the epidermis to dermis and subcutaneous tissue.
• Stage4: Migration
  • On reaching the subcutaneous tissue, the larva enters into the lymphatic small vessels.
  • They pass through the lymph-vascular system into the venom circulation and carried via the right heart into the pulmonary capillaries.
  • They break the lung capillaries and enter into the alveolar spaces.
  • They then ascend upward the bronchial tree to trachea and larynx, crawl up over the epiglottis to the back of pharynx and ultimately swallowed.
  • During migration or entering the esophagus, the larva undergoes a third moult to form fourth stage (L4 larva) equipped with a buccal capsule allowing adherence to the gut wall.
• Stage5:  Localization and laying of eggs
  • The growing larva settle down in the small intestine, undergo a fourth moult to develop into an adolescent worm.
  •  At this stage, the provisional toothless buccal capsule formed is cast off and definitive buccal capsule complete with teeth is formed.
  •  During 4-5 weeks, the adults who remain attached to mucosa of the small intestine becomes sexually mature.
  • The fertilized females begin to lay eggs which are excreted out in the feces.
  • The cycle is thus repeated.
  • The interval between the time of skin infection and the first appearance of eggs in feces is about 6 weeks.

Mode of transmission:

• Human feces are the only source of infection.
•  The route of infection transmission:
  • Cutaneous route: Penetration of the skin by infective filariform larva
  • Oral route: Ingestion of L3 larva present in the soil, occurs less frequency. Larva in mouth develops directly into adult worms.
  • Transmammary transmission: Breast feeding by mothers to infants.
  • Very rarely, trans-parental transmission.

Pathogenesis:

Pathogenicity of adult worm:

• The major pathological changes in ancyclostomiasis are caused by the attachment of adult worms to the intestinal walls by their buccal capsule.
• The common site of infection is the upper small intestine.
• The attachment of parasite leads to mechanical disruption of intestinal mucosa of the resulting ‘mucosal plug’ lodged within the worm’s buccal capsule.
• These parasites penetrate the blood vessels with their mouth parts and suck the blood to get the nutrition.
• These worms cause considerable loss of blood and tissue.
• The adult Ancylostoma can suck about 0.2 ml blood a day while smaller Necator suck about 0.03 ml per day.
• The secretions of the site may continue for sometimes, this add to blood loss.
• Excessive blood loss caused by heavy and prolonged worm infection leads to hypochromic microcytic anemia.

Pathogenicity of infective larva:

• The infective filariform larva at the site of the penetration of the skin, produce a local reaction called ground itch.
•  This allergic manifestation is more severe in Necator infection
•  In previously sensitized host, it can lead to secondary bacterial infections.
• The migration of large no. of larva, through the lung produces minute hemorrhage and infiltration of leucocytes resulting in the entrapment of the larva in lung tissue.
• Both eosinophilia and leukocytosis occur at this stage.

Clinical manifestation:

The clinical symptoms depend on the site where the worms are present and their burden.

1. Skin infection:

• Hookworm related cutaneous larva migrans (HrCLM) is a parasitic skin disease caused by migration of hookworm larva in the epidermis.
• Ground itch is the early clinical manifestation during the penetration of L3 larva on the skin. It is believed to be due to allergic components of the larva.
• Lesions are characteristically seen in and around feet particularly between the toes.
• It is associated with intense itching, edema and erythema and rash.
• The associated secondary bacterial infection is more common during this stage.

2. Pulmonary infection:

• It is associated with low grade fever, mild cough dizziness and hemolysis.
• Pneumonia with pulmonary consolidation is seen in persons with severe infection.

3. Intestinal infection:

• Acute intestinal symptoms such as abdominal pain, nausea, vomiting and hemorrhagic diarrhea are observed.
• Chronic hook worm disease is characterized by blood loss and Ion-deficiency anemia and is associated with fatigue, pallor, tachycardia and dyspnea on exertion.
• Hypoproteinemia may cause edema and there can be sign of malabsorption and malnutrition.
• In children there may also be adverse effects on physical growth and intellectual growth.
• The severity of the disease varies with the worm burden and the amount of blood lost heavy infections can be fatal, particularly in infants.

Laboratory diagnosis:

• Specimen:
  • Stool, duodenal content obtained by the duodenal intubation (Ryles tube) may sometimes reveal either egg or the adult worms.

 1. Stool microscopy:

• A specific diagnosis of hookworm infection is based on the microscopic identification of eggs.
• This is carried out by examination of a direct wet mount of the stool.
• In case of light hook worm infection, detection of eggs can be done using concentration methods-formalin ether concentration technique or simple salt floatation technique.
• Kato-Katz is a useful method for quantitation estimation of hook worm eggs present in the stool.
• The intensity of the infection is determined by counting the no. of eggs in a measured volume of feces.

2. Stool culture:

• Harada- mori method of culture of stool is carried out to demonstrate L3 larva.
• The eggs present in the stool are smeared in moist filter paper, after an incubation of 5-7 days at room temperature, L3 larva hatch out of eggs.

3. Imaging methods:

• On chest X-ray a patchy infiltrate may be demonstrated in the migratory phase of larva in the lungs.

4. Blood test:

• This is carried out to ascertain the nature of anemia and the presence of eosinophilia.

5. Occult blood test:

• occult blood in the stool gives a position reaction in case of hookworm infection
• Charcot-Leyden crystals are often found in the stool.

Treatment:

• Mebendazole is a drug of choice- oral, 100 mg twice daily for 3 days
• Others anti parasitic drugs are- pyrantel pamoate, thiabendazole, Albendazole, levamisole
• Treatment of iron deficiency anemia with replacement iron therapy.

Prevention:

• Sanitary disposal of human feces
• Treatment of infected persons.
• Use of sanitary latrines, use of foot wears.
• Health education with improved nutrition supplemented with the dietary iron.

Epidemiology:

• Hookworm infections are the second most common helminthic infection next to ascariasis.
• The infection in worldwide is distribution more commonly in areas with warm and moist climate.
•  Approx. 1200 million people are infected worldwide.
• Ancylostoma is found in Europe around the Mediterranean, on the west of South America and in parts of China, India and Nepal.
• Necator is found much over of the western Hemisphere, Africa and South East Asia.

Hookworm infection: life cycle, transmission, pathogenesis, diagnosis and treatment

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