Hookworm infestation

Hookworm infestation

1. Hookworm
Introduction
• Widely distributed in tropical and sub tropical countries
• One of small intestine nematodes
• Important cause of Iron deficiency anaemia
• Named so – anterior end of adult worm is bent
• Belongs to family Ancylostomatidae
• 2 important human Species: Ancylostoma duodenale, Necator americanus

Ancylostoma duodenale
• Also called old world hookworm
• Causes ancylostomiasis
• Dubini in 1843 described the parasite
• Arthur Loss in 1896 described pathogenesis and mode of infection

Epidemiology
• Globally 900 million people infected. Necator- 835 million & Ancylostoma- 135 million • Hookworm
infection is prevalent in the tropics and subtropical countries – Asia, Africa, America, China and Southern
Europe
• In India – prevalent in Punjab, Uttar Pradesh and Bihar
• Males & young adults commonly affected
• Anaemia severe in children & pregnant women

Morphology
Adult worm
Adult Worm:
• Life span adult worm in human intestine: 3 to 4 years



Egg
• Egg floats in saturated salt solution
• Single female worm- lays about 25 000 to 30 000 eggs/day
• Eggs are excreted in faeces 4-7 weeks after infection

Life cycle of Hookworm
• Definite host: man

In small intestines: Adult worm inhabit small intestine of man
• Attachment to mucous membrane by help of mouth parts
• Eggs contain segmented ova with 4 blastomeres- passed out in faces of infected person (non-infective)

In soil: rhabditiform larva hatches from each egg (24- 48 hours)
• size: 250 µm x 17 µm.

2. • moults twice on 3rd and 5th day
• develops into filariform larva.
→ size: 500-700 µm long
→ is the infective form- penetrates unbroken skin (of toes, dorsum of foot and medial aspect of sole)
→ Remains infective up to 6 weeks

People at risk:
• Walking barefoot on soil containing filariform larva
• Farm workers: larva penetrates skin of hands

• reaches subcutaneous tissues and enters lymphatics or small venules
• Lymph to venous circulation into right heart
• into pulmonary capillaries- break through and enters alveolar spaces
• migrates to bronchi, trachea and larynx- crawl over the epiglottis to pharynx → gets swallowed
• During migration through oesophagus → undergo 3rd moulting
• Settles in small intestines → undergo 4th moulting and develop into adult worms.
• Attach to small intestine by their mouth parts
• After 6 weeks- mature sexually
• Fertilization occurs
• Female begin to lay eggs in faeces → cycle repeats

Pathogenesis and clinical manifestations
• Infective form: filariform larva
• Portal of entry- skin
• Worm causes hookworm disease- characterized by anaemia.
• Effects are due to –migrating larva or adult worm

• Migrating larva lesions:
→ Ancylostoma dermatitis or ground itch
→ Creeping eruption or cutaneous larva migrans
→ Lesions in lungs

Ancylostoma dermatitis/ground itch
• Occurs at site of entry
• Entry of filariform in skin cause dermatitis
• Leads to intense itching and burning
• Followed by erythema and oedema of the area
• Develop into papular and vesicular eruptions
• Disappears within 1 to 2 weeks.
• Common in N. americanus

Creeping eruption/cutaneous larva migrans
• Condition where filariform larva wander about the skin
- producing reddish itchy papule along path traversed by the worm Seen mostly in animal (cats, dogs
and others)
- Animal filariform cannot penetrate below level of stratum germinativum and stratum corneum

Animal agents:
- Ancylostoma braziliense (dogs and cats)
- A. caninum (dog hookworm)
- Uncinaria stenocephalia (dog hookworm)
- Bunostomum phlebotomum (cattle hookworm)
- Gnathostoma sp.

3. • Human- infected by walking barefoot → contacting moist soil contaminated with animal faeces
• Creeping eruptions may occur occasionally by A. duodenale and N. americanus.

Lesions in the lungs
• Bronchitis and bronchopneumonia
• Marked eosinophilia occurs
• Caused by adult worm
• Disease= hookworm disease
• Features:- microcytic hypochromic anaemia
• Hookworm ingest blood
• Other features: cough, dyspnoea

Intestinal manifestations
• Attach to mucosa of small intestines
• Adult worm of A. duodenale sucks more blood (0.2 ml/day) than for N. americanus.
• Worm migrate to another site leaving small bleeding points
• Worm secretions possess anticoagulant activity → bleeding from sites continue for sometimes.
• These leads to iron deficiency anaemia of microcytic, hypochromic type
• Degree of anaemia depends on: number of worms, body iron store, dietary iron
• Development of low grade fever, epigastric pain, dyspepsia, vomiting and diarrhoea.
• Stool: reddish to black
• Symptoms and signs of anaemia present.

Laboratory Diagnosis
Direct Methods:
• Stool examination: to find the adult worm or characteristic hookworm eggs
• Stool concentration: required to detect light infections
• Larva- seen if stool is kept at room temperature after 24 hours (not preserved)
• May resemble Strongyloides larvae
•Adult female hookworm- produce 2500 to 5000 eggs/day.
- Stool egg count: indicates number of adult hookworms present
• Indicates severity of infection
- Duodenal contents- reveals eggs or adult worms.

Indirect methods:
• Blood examination: reveals microcytic, hypochromic anaemia and eosinophilia
• Stool exam: shows occult blood and Charcot-Leyden crystals

Stool culture:
• Eggs hatch out and develop into filariform larva (L3) stage
• Takes place in 5-7 days

Culture techniques used:
• Harada Mori filter paper tube method
• Petridish (slant culture) technique - Baermann funnel technique - Charcoal culture method - Agar plate
technique (more sensitive) Other findings: hypochromic microcytic anaemia Chest x-ray- show patchy
infiltration of lungs

Necator americanus
• Has similar life cycle, pathogenesis and lab diagnosis like for A. duodenale.
• Adult worm- slightly smaller than Ancylostoma
• Eggs of Ancylostoma and Necator are similar and hence can be differentiated by morphological study of
adult worms and larvae

4. Epidemiology
• Western world- Africa and America
• In India – all except in Punjab, Uttar Pradesh

Treatment
• Mebendazole- 100 mg twice daily for 3 days
• Albendazole- 400 mg single dose
• Pyrantal pamoate – 11 mg/kg for 3 days
• Mild iron-deficiency anaemia- oral iron
• Severe infections with protein loss and malabsorption: nutritional support and oral or parenteral iron
replacement

Prevention
• Personal care:
- improved personal hygiene
- proper disposal of faeces
- improved nutrition with dietary iron
- treatment of infected persons
• Prophylaxis: experimental animal vaccines: using larval or adult stage antigen.
• Human trials: targeting Ancylostoma secreted proteins (ASP).