ANCYLOSTOMIASIS (HOOKWORM)

The hookworms
most infections by adult worms are due to:

1. Ancylostoma duodenale

2. Necator americanus.

ANCYLOSTOMIASIS (HOOKWORM) 

Epidemiology, MORPHOLOGY AND LIFE CYCLE:

Ancylostomiasis is caused by parasitisation of the small intestine with Ancylostoma duodenale or Necator americanus. It is one of the main causes of anaemia in the tropics. In the early stages of infection eosinophilia is common. The adult hookworm is 1 cm long and lives in the duodenum and upper jejunum. Eggs are passed in the faeces. In warm, moist, shady soil the larvae develop into the filariform infective stage; they then penetrate human skin and are carried to the lungs. After entering the alveoli they ascend the bronchi, are swallowed and mature in the small intestine, reaching maturity 4-7 weeks after infection.  Hookworm infection is widespread in the tropics and subtropics. A. duodenale is endemic in the Far East and Mediterranean coastal regions and is also present in Africa, while N. americanus is endemic in West, East and Central Africa and Central and South America, as well as in the Far East.

The larvae may cause allergic inflammation at the site of entry through the skin. When infection is heavy, the passage through the lungs may cause pulmonary eosinophilia. The worms attach themselves to the mucosa of the small intestine by their buccal capsule and withdraw blood. The mean daily loss of blood from one A. duodenale is 0.15 ml and from N. americanus 0.03 ml.

The degree of iron and protein deficiency which develops depends not only on the load of worms but also on the nutrition of the patient and especially on the iron stores. In a light infection there may be no anaemia.

Clinical features:

Dermatitis, usually on the feet (ground itch), may be experienced at the time of infection. The passage of the larvae through the lungs in a heavy infection causes a paroxysmal cough with blood-stained sputum, associated with patchy pulmonary consolidation. When the worms have reached the small intestine, vomiting and epigastric pain resembling peptic ulcer disease may occur. Sometimes frequent loose stools are passed. Iron deficiency anaemia, protein-losing enteropathy and hypoproteinaemia may develop in the undernourished. High-output cardiac failure may result from the chronic iron deficiency anaemia. The mental and physical development of children may be retarded. A well-nourished person with a light infection may be asymptomatic.

Investigations 

There is eosinophilia. The characteristic ovum can be recognised in the stool. If hookworms are present in numbers sufficient to cause anaemia, faecal occult blood testing will be positive and many ova will be present. 

Management 

Mebendazole 100 mg 12-hourly for 3 days is preferred, but for single-dose treatment albendazole (400 mg) is the best choice. Anaemia associated with hookworm infection responds well to oral iron. The management of anaemic heart disease is best accomplished by treatment with anthelmintics and iron. Blood transfusion should only be used with great care in very severely anemic patients (< 40 g/l).