Hookworm: Introduction, Morphology, life cycle, mode of infection

Hookworm: Introduction, Morphology, life cycle, Mode of Infection, Pathogenecity, Lab Diagnosis and Treatment

Hookworm

Hookworm is intestinal, blood-feeding, roundworm parasite that causes types of infection known as helminthiases and which is a common infection in countries with poor access to adequate water, sanitation, and hygiene. In humans, hookworm infections are caused by two main species of roundworm belonging to the genera Ancylostoma and Necator.
Scientific classification

Kingdom: Animalia

Phylum: Nematoda

Class: Chromadorea

Order: Rhabditida

Family: Ancylostomatidae

Genus: Ancylostoma

Species: A. duodenale

Binomial name Ancylostoma duodenale

Scientific classification

Kingdom: Animalia

Phylum: Nematoda

Class: Secernentea

Order: Strongylida

Family: Ancylostomatidae

Genus: Necator

Species: N. americanus

Binomial name

Necator americanus

Geographical distribution of Hookworm

All tropical and subtropical countries (Europe, North Africa, India, China, America)Occurs in all places wherever humidity and temperature are favorable for the development of larva.

Habitat

Lives in the small intestine of man Jejunum (most) but also in the duodenum (less) and Ileum(rare).

Morphology of Hookworm

Adult hookworm

Male hookworm:

Size: Smaller ( 8-11 mm long ×0.45 mm)

Posterior end: Umbrella like expansion

Genital opening: Posteriorly opens with cloaca.

Female hookworm

Size: Larger ( 10-13 mm long ×0.6 mm)

Posterior end: Tapering no umbrella-like expansion

Genital opening: At the junction of the posterior and middle third of the body

Egg

Shape: oval or elliptical with flattened poles( one pole more often flattened than other), size: 65 X 40 um, color: colorless ( no bile stain), dark brown as stained with iodine. Shell: very thin transparent hyaline shell membrane, appears as a black line and contains: segmented ovum with 4 blastomeres, has a clear space between eggshell and segmented ovum. Float in saturated NaCl. Type: A( fresh stool) : 4 ,8, 16 grey granular cell clear blastomeres. Type: B( few hours old): a uniform mass of many grey granular cells. Type: C( 12-48 hr): the whole egg is filled with larva, embryonated.

Life cycle of Ancylostoma duodenale

Definitive host: Man No intermediate host

Stage 1: Passage of eggs from the infected host
Stage 2: Development in soil

From each egg, a rhabditiform larva (250um), feeding stage of larvae, hatches out in the soil in 48 hr, molt twice on 3rd and 5th day and develops into filariform larva. Filariform larva ( extremely motile nonfeeding stage of larvae,5 00 to 600 um) is an infective stage. The time taken for the development from eggs to filariform larvae is an average of 8 to 10 days.
Stage 3: Entrance into the new host: The larva cast off their sheath and gain entrance to the body by penetrating the skin.

Stage 4: Migration larva enter into lymphatics or small venules, pass into the venous circulation, and are carried into the right heart into pulmonary capillaries where they break through the capillary wall and enter into the alveolar spaces Migrate into bronchi, trachea, and larynx, crawl over the epiglottis to back of pharynx and ultimately swallowed. On the esophagus third molting takes. Period for migration: 10 days
Stage 5: Localization and laying of eggs. Four moltings in the small intestine. Buccal capsule with complete teeth is formed in 3 to 4 weeks and they are sexually matured and the fertilized female begins to lay eggs in the feces.

Mode of infection

Filariform larvae penetrate directly through the skin with which they come in contact. Site of entry: skin

Thin skin between toes

Dorsum of the feet

The inner side of the sole

Skin of hands

Pathogenicity of Ancylostoma duodenale

Ancylostoma dermatitis (ground itch)
Creeping eruption
Bronchitis and bronchopneumonia
Anemia due to – chronic blood loss may be due to parasite sucking blood or hemorrhage from sites of attachment of hookworms and nutritional deficiency

Clinical feature of hookworm anemia

Gastrointestinal manifestation: Duodenal ulcer, abnormal appetite, analysis of gastric acidity show hypo acidity; IDA cause low secretion of gastric acid, steatorrhea, constipated bowel ( less bowel movement)
Effects of Anemia: Pallor of the mucous membrane of eyes, lips tongue, and skin Edema of feet and ankle (pitting on pressure), Koilonychia ( spoon nail). The general appearance of the patient is a pale plump individual with a protuberant abdomen and dry lusterless hair.

Laboratory diagnosis of Hookworm

A direct microscopical examination of stool (wet mount preparation), concentration technique may be used. Duodenal intubation may reveal eggs or adult worms. Indirect method- Examination of blood: Eosinophilia, occult blood test: positive, serologic tests for hookworms, including ELISA and immunoblotting (Western blotting). Presence of Charcot-Leyden crystals in the stool.

Treatment

Treatment of Anemia with Iron first if Hb is below 30 percent.
Antihelmintic drugs-Thiabendazole, pyrantel pamoate, mebendazole, albendazole, levamisole, tetramisole, and bephenium hydroxynaphthoate.

Prophylaxis

Attack on adult parasite: treatment of carrier and diseased person.
Attack on larvae: prevention of soil pollution by proper control of sewage disposal.
Disinfection of feces or soil.
Personal protection: wearing of boots and gloves.

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