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Ectoparasites 215

attaches itself to the hairs of the head and is best known
MACROSCOPIC DIAGNOSTIC for causing outbreaks in schoolchildren. This is a com-

FEATURE (REQUIRES mon occurrence in some crowded schools and the
organisms spread rapidly. Because the pubic, or crab,
MAGNIFYING GLASS IN SOME louse called P.hthirus pubis is most often sexually trans-
CASES) mitted, it prefers the environment of the moist and dark
areas found in regions of the body. The louse resembles a
miniature crab and causes intense itching in pubic areas,
General Classification—Louse
but it can also infect the eyebrows, eyelashes, and beards.
Organism Pediculus humanus The two species of lice that afflict humans are
var. corporis scavengers that feed on the skin and other debris found
Specimen Required Epidermal tissue or on the host’s body. But some species will also feed on
individual organism sebaceous (sweat gland) secretions and blood. Most are
Stage Organism and its nit, found only on specific types of animals, and in some
or egg, on hair cases, they are confined to only a specific part of the
Color & Appearance White-gray to brown body. Some animals are known to host up to 15 differ-
Size Egg is 0.8 mm, adult ent species simultaneously, although 1 to 3 is typical for
slightly larger mammals and often 2 to 6 may be commonly found on
(1.5 mm) birds. For example, in humans most of the different spe-
Shape Elongated, crablike cies of the louse inhabit the scalp and pubic hair. Lice
Motility No wings or ability generally cannot survive for long if removed from their
to jump; move by host as they are unable to live freely in the environment
crawling as is the case for some organisms. So cleaning living
quarters would be quite effective in preventing infesta-
P. humanus corporis organism tions and reinfestations.
Because lice live chiefly in the head hair and in the
pubic hair of the body, they are somewhat easy to control
through sanitation and medication. The louse’s color
varies from pale beige to dark gray, but when feeding on
blood the organism may become considerably darker
and therefore blends in well with the hair of a human.
This makes them all but invisible to the naked eye. Just
keeping the hair clean is not a deterrent to these lice as
they prefer clean hair to dirty hair. Female lice are usually
more common than males in most species, but some spe-
Delmar/Cengage Learning that they may self-fertilize themselves for reproduction.
cies are even known to be parthenogenetic, which means
A louse’s egg is commonly called a nit, commonly at-
taches to a hair shaft, and is how most infestations are
discovered as nits are easily seen (Figure 10-2).
As the nit is more readily visible, it is often the first
sign that a child may be infected with head lice even
Close contact with an infected person is required for before symptoms appear. Many lice attach their eggs to
transfer of the organism between humans and other their host’s hair with specialized saliva, which makes
mammals because lice cannot jump or fly to other vic- the bond very difficult to break without specialized
tims. The human body louse, called Pediculus humanus products such as shampoos designed to sever this bond
corporis, lives on the body and clothes of humans. The as well as to kill the organisms. More than one treat-
head louse, which is called Pediculus humanus capitis, ment is necessary as some of the reproductive stages