Figure 1-11. Life cycle of the louse.
a. The Body Louse, Pediculus humanus humanus. The body louse (see
figure 1-12) is the common clothing louse and is the vector of epidemic louse-borne
typhus, as well as epidemic relapsing fever. In World War I, soldiers referred to the
body louse as a "cootie" or "grayback." Body Iice are most common where the clothes
are in close contact with the body. Eggs are laid in the seams of clothing where it
comes in close contact with the body, for example, underwear, the crotch of the
trousers, the waistline, etc. Depending on where the eggs are laid, incubation of eggs
requires 5 to 10 or more days. After hatching, the young Iice start to suck blood at
once; throughout their development, they feed frequently, particularly at times when the
host is quiet. The total development time averages about 3 weeks, from egg to adult.
At maturity, the female begins to lay from four to as many as 10 eggs per day. She can
Iive from 20 to 30 days, and can lay up to 300 eggs in her Iifetime. Body Iice thrive best
in areas of the world where heavy to moderately heavy clothing is worn. Of the three
species of human Iice, body Iice survive the longest away from the host (up to 10 days),
and are the most active. They are well known to leave a feverish host or one that has
grown cold in death. It is easy to see why they are a problem in times of war.
b. The Head Louse, Pediculus humanus capitis. This species is generally
restricted to the head, where it commonly concentrates around the ears and at the base
of the hair Iine near the neck. The head louse is similar in appearance to body louse
(see figure 1-12), but is smaller. It is apparently of no importance in the spread of
disease. In severe infestations, the hair may become matted with eggs and exudates
from the pustules that originate from the louse bite. The female cements her eggs to
the base of the hair, near the scalp. The cement is very persistent, and cannot be
dissolved without harming the hair or the scalp. The empty eggshell thus remains in the
hair long after the young louse has emerged, and does indicate an active infestation.
Eggs have an incubation period of about 8 to 9 days, for a total development period of
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