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13
Ectoparasites of Medical Importance

General Characteristics of Mites and Lice

The parasitic mites and lice are mainly ectoparasites. Mite is of the order Acarina.
Louse is of the order Anoplura (sucking louse).

Sarcoptes scabiei

Distribution
This mite has a cosmopolitan distribution especially in crowded environment.
It causes scabies and its infestation is more common in slumps, jails and
orphanages.

Habitat
Skin of human.
Morphology
Sarcoptes scabiei is a small, oval, dorsally convex, ventrally flattened mite. The male
measures 200–250 μm and the female measures 330–450 μm. It has 4 pairs of legs.
The first 2 pairs of legs terminate in long tubular processes, each with a bell-shaped
sucker (Fig. 13.1). The posterior 2 pairs of legs end in long bristles, but in males, the
fourth pair have suckers. The dorsal surface bears spines, scales and bristles.

Life Cycle
The mites live in serpiginous cutaneous burrows. Both male and female mites bur-
row into the corneous layer of the skin. The female deposits up to 40–50 eggs in the
burrow during its lifespan of 4–5 weeks. Hexapod larvae emerge from the eggs in
3–10 days. The larva develops into an eight-legged nymph which later matures into
adult stage. The life cycle is completed in 8–15 days.
Scabies is transmitted by close personal contact with an infected person.

© Springer International Publishing AG 2017 151
R. Mahmud et al., Medical Parasitology,
https://doi.org/10.1007/978-3-319-68795-7_13