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Intestinal Nematodes: Soil-Transmitted Helminths (STH) 91

Fig. 10.9 Hookworm
L3 larva (with pointed
tail)

pharynx. They are then swallowed and develop into adults in the lumen of the small
intestine in 1–2 months. The adult female deposits eggs which are excreted into the
faeces.
Both hookworms have similar life cycle. L3 larva is the infective stage (Fig. 10.9).
The lifespan of Necator is more than 4 years and Ancylostoma is 2–7 years.

Pathogenesis and Clinical Features
When the filariform larva penetrates the skin, it causes severe local itching called
ground itch. Erythematous papular rash develops when a large number of larvae
penetrate the skin.
Loeffler’s syndrome may occur in heavy larvae infection.
Hookworm infection is usually asymptomatic. Adult worms suck blood aided
by the anticoagulant that they secrete. The worms change feeding sites and the
old biting sites will continue to bleed. Stool may become black in colour
(malaena). Chronic infection can lead to iron deficiency anaemia. Patients may
present with features of anaemia such as exertional dyspnoea, tiredness, palpita-
tions and dizziness. Severe hookworm anaemia may lead to cardiac failure and
hypoalbuminaemia.

Diagnosis
1. Microscopic examination
Detection of characteristic hookworm eggs in faeces by direct wet micros-
copy or by concentration methods. Delayed examination of stool samples may
cause eggs to hatch and rhabditiform larvae may be present. These have to be
differentiated from Strongyloides larvae by doing stool culture. L3 of hookworm
has pointed tail whereas L3 of Strongyloides has notched tail.
2. Stool culture
Harada Mori method of stool culture is carried out to demonstrate third-stage
filariform larvae.