[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

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CHAPTER 13 The Arthropods
Quick Quiz! 13-2
Arthropods that live in or on human skin are referred
to as which of the following? (Objective 13-1)
A. Larvae
B. Pronotal ctenidia
C. Ectoparasites
D. Pupae
TREATMENT
Topical lotions or ointments are available for the
treatment of arthropod bites. Treatment of ectoparasite
infestations requires the removal of the
arthropod from the skin. Additional treatment
regimens are also required for patients who contract
a disease from an arthropod. As with clinical
symptoms, specific treatments for parasitic
infections have been discussed elsewhere in this
text and will not be repeated in this chapter. The
treatment of arthropod bites and infestations
will, however, be briefly discussed and individually
noted in this chapter.
PREVENTION AND CONTROL
Complete eradication of arthropods is almost
impossible. It is essential to know the geographic
distribution and life cycles of the arthropod, and
the disease it carries, as well as their environmental
reservoirs and the diseases that these may
transmit. Some arthropods can transmit the
microorganism they carry to their offspring, a
process known as vertical transmission, creating
a permanent reservoir in the environment and
making the disease more difficult to contain.
Although chemical sprays and insecticides are
available, they are often not financially feasible
or physically possible to distribute over vast
areas. In addition, many species of arthropods
have adapted to commonly used chemicals,
becoming resistant and surviving after chemical
spray contact. There is also concern that chemical
sprays and insecticides may harm the
environment. Other potential control measures
include the destruction of arthropod breeding
grounds, increasing natural predators, and the
use of protective clothing and arthropod repellents,
when appropriate, to prevent exposure.
ARTHROPOD CLASSIFICATION
The phylum Arthropoda contains five classes of
medically significant arthropods (Fig. 13-1).
Although members of each of these arthropod
classes are shown in this figure, only the most
common organisms will be discussed in this
chapter—those belonging to the class Arachnida
(e.g., ticks, mites, spiders, scorpions) and class
Insecta (e.g., fleas, flies, lice, mosquitoes, bugs).
An in-depth study of all the arthropods is beyond
the scope of this text. Readers interested in
arthropods other than those described here are
encouraged to review the Bibliography located at
the end of this text (Appendix E).
Ticks
Quick Quiz! 13-3
Vertical transmission occurs when an arthropod does
which of the following? (Objective 13-1)
A. Bites a unsuspecting human
B. Ingests human blood
C. Passes infective agents to offspring
D. Comes in contact with insecticides
Morphology
Adult ticks, like all arachnids, characteristically
have four pairs of legs, two pairs of mouth parts,
and no antennae (Fig. 13-2; Table 13-1). Ticks
are of the order Ixodida, which contains the
family Ixodidae (hard body) and the family
Argasidae (soft body) ticks. Both types of ticks
are somewhat oval in shape. The head, thorax,
and abdominal regions are meshed together and
appear as a single structure. Ticks have four pairs
of legs and lack antennae and a head region.
Sexes are separate.
There are two major morphologic differences
between hard and soft ticks. Both types of ticks
have an anterior capitulum, an umbrella term referring
to the mouthparts of ticks and mites. This