Section XI. LOUSE-BORNE DISEASES
Louse-borne diseases have always been a threat to fighting forces. Lice
are particularly associated with cold weather, and, while they are also
present in the higher altitudes of the tropics, they are found more
commonly in temperate and subarctic areas where clothing is heavy and is
worn in several layers. Three species of lice are of medical importance:
the body louse, the head louse, and the crab louse. All go through the life cycle
depicted in Figure 5-18.
Figure 5-18. Life cycle of lice (Pediculus humanus corporis).
a. The Body Louse. The body louse (Pediculus humanus) is the vector of
epidemic (louse-borne) typhus and epidemic relapsing fever.
(1) Nits. The body louse attaches its eggs to the fibers of clothing, especially
along the seams, and rarely to body hairs. The eggs (nits) are white in color, oval in
shape, have a lid on one end, and are about the size of the period at the end of a
sentence. At temperatures of from 86 to 90 F, eggs will hatch into nymphs in about 8
days; but at lower temperatures the hatching process may take 2 weeks or more.
(2) Nymphs. Nymphs are similar to the adult, except that they are much
smaller (pinhead size). Unless they obtain a meal of blood within 24 to 48 hours after
hatching, the nymphs will die. The nymphal stage lasts about 9 days, after which the
louse is a mature adult.
(3) Adult louse. Adult females begin to lay eggs 4 days after maturity, at the
rate of from 5 to 10 eggs a day. Under favorable conditions, they will continue the