Page 236 - parasitology for medical and clinical laboratoryprofessionals

216 CHAPTER 10

are less sensitive to the special shampoo than others
and repeat applications will kill the next stage as it ma-
tures. Lice inhabiting birds, however, may simply leave
their eggs in parts of the body that are inaccessible to
preening, such as the interior of feather shafts. Lice that
almost exclusively inhabit birds may briefly infest hu-
mans but will not survive for a sufficient period of time
for reproduction.
Source: Centers for Disease Control and Prevention (CDC) life cycle because they are born as small adults called
Living lice eggs tend to be pale white, whereas
dead lice eggs are yellowish in color. Lice have a simple

nymphs, and as they molt, or shed, their skin they
become larger in size as they progress toward adulthood.
Organisms that reproduce in this manner are known as
being hemimetabolous. After three sequences of molt-
ing, the lice are in the final adult form, which usually
occurs within a month of hatching from the egg. Lice

bedding, clothing, and furniture (Figure 10-3).
FIGURE 10-2 The nit, or louse, eggs are glued to are transmitted through close contact and from infested
hairs of a host
OTHER COMMON ECTOPARASITES

Although not as common as the lice previously discussed,
the following are some other common ectoparasites that
may not be as common as the previous three. However,
they may sometimes be found in endemic proportions.

Mites
A number of members of the order Acarina are called
mites and are nuisances to both humans and animals in
some cases. Mites are minute arthropods, some of which
are parasitic and cause a variety of conditions in humans
and in domestic animals (Figure 10-4). In addition, a
Source: Centers for Disease Control and Prevention (CDC) diseases. In some cases they may also serve as the inter-
few serve as vectors of disease organisms such as viruses
and bacteria that contribute greatly to somewhat serious

mediate host for some species of cestodes, commonly
known as tapeworms, and therefore transmit other
microorganisms. Asthma may be caused, or exacerbated,
by mites.
Although similar to ticks, mites differ considerably

to their minute size. The fact that they may be either al-
most clear (transparent) or they may be semi-transparent
makes it more difficult to visualize them. Colloquially,
FIGURE 10-3 Body lice are parasitic insects that live on in size as they are quite small and are difficult to see due
the body and in the clothing or bedding of infested humans they are sometimes called either chiggers or redbugs.