Land leeches are common in South-east Asia, the Pacific islands, the Indian subcontinent and South America. Aquatic leeches have a worldwide distribution.

Leeches that attack humans have the following position in the animal kingdom:

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Gnathobdellida leeches are invertebrates, having a smooth cuticle, a mouth lacking a proboscis but with three jaws, two suckers (one surrounding the mouth, the other at the posterior end) and powerful muscles, circular and longitudinal. They attach themselves by the posterior sucker, the anterior end moving about freely. When unfed, they are usually about 2.5 cm long and 5 mm thick; some are bigger. When full of blood they are dark, bloated objects.

The muscular jaws are covered with chitin and produce a characteristic …