Page 160 - Medical Parasitology_ A Textbook ( PDFDrive )

General Characteristics of Mites and Lice 153

4. Ivermectin, oral drug is used for patients with altered immune systems, crusted
scabies, or those who do not respond to the prescription lotions and creams (not
for children below 5 years old).

The cream/lotion should be applied to all skin surfaces for 8–12 h and then
washed off. Treatment should be repeated in a week if infestation is still pres-
ent. Secondary bacterial infection in scabies has to be treated with antibiotics.

Prevention and Control
1. Treatment of infected individuals
2. Sterilization of garments and beddings
3. Personal cleanliness

Lice

Distribution
Lice are exclusively human parasites and have a worldwide distribution.

Habitat
The parasitic lice of humans include 3 species:

1. Pediculus humanus capitis (head louse)
2. Pediculus humanus humanus (body louse)
3. Phthirus pubis (crab louse/pubic louse)

Morphology
Lice are small, dorsoventrally flattened, wingless insects. The insect has a head, tho-
rax and abdomen. The thorax has 3 segments and each segment bears a pair of strong
legs that terminate in a single hook-like claw. Both body and head lice are identical,
and they measure 2–3 mm in length (Fig. 13.2). The body louse is more robust.
The crab louse is small, measuring 0.8–1.2 mm, oblong with rectangular head,
short-segmented abdomen and 3 pairs of legs with big claws arising from the thorax
(Fig. 13.3).
The eggs (nits) are operculated, white in colour, measuring 0.6–0.8 mm and are
deposited and firmly attached to the hairs (head louse and crab louse) or to the fibres
of clothing (body louse).

Life Cycle
After eggs are deposited by the female louse, they hatch in 5–11 days. The nymph
develops within the egg case and emerges through the opened operculum. It under-
goes 3 moults within 2 weeks. The life cycle of body/head louse takes 18 days and
that of crab louse 15 days. The lifespan of the adult is about 1 month.
The lice are readily transmitted from host to host through close contact. The head
louse is easily transmitted by brushes, combs and hats. It is most prevalent in school