[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

CHAPTER 13 The Arthropods
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(2) a chitinized exoskeleton (defined as a structure
on the outside of an arthropod body
composed of an insoluble polysaccharide that
provides support for corresponding internal
organs); and (3) a system of blood-containing
spaces present on the body of an arthropod
referred to as a hemocele. Other general arthropod
characteristics include bilateral symmetry;
often, more than one life stage is involved in
human interaction. The specific morphologic
forms and life cycle phases vary among the
arthropods discussed in this chapter and are
covered on an individual basis.
LABORATORY DIAGNOSIS
Although ectoparasites (parasites established in
or on the exterior of the body) can be examined
directly, it may be helpful to immerse them completely
in 70% ethanol as a preservative. Flying
insects may require inactivation with chloroform
or ether before immersion in alcohol. This
alcohol solution will maintain the morphology
and color until examined. Samples may also be
placed in 5% formalin or sterile saline solution.
Some arthropods may discolor after a few days
in formalin and sterile saline will not prevent
eventual decomposition. Berlese’s medium can be
used as a permanent method to kill and fix
specimens.
Although most of the arthropods in this
chapter are directly visible, some stages are
extremely small and microscopic examination is
necessary to discern specific features. Arthropods
may be diagnosed by placing them on a glass
slide and examining them under the microscope
or dissecting microscope. The distinguishing
arthropod morphology characteristics necessary
for identification are usually readily recognized
on examination.
The laboratory diagnostic techniques described
here basically apply to the identification of all the
arthropods in this chapter, thus eliminating the
need for individual laboratory diagnosis section
discussions. Readers may refer back to this
section for laboratory diagnosis information.
Quick Quiz! 13-1
All arthropods possess a hemocele at some point in
their life cycle. (Objective 13-6)
A. True
B. False
C. Unable to determine
ARTHROPOD-HUMAN
RELATIONSHIPS
Arthropods may affect humans in various ways.
They may take up residence as temporary or
permanent occupants of their human host or
they may cause the disease themselves. Arthropods
may also transmit disease as mechanical
transfer agents, such as house flies or cockroaches
transmitting bacteria that cause enteric diseases
(e.g., typhoid, cholera). Some arthropods are an
actual part of the parasite’s life cycle and are
involved in direct transmission via blood meals
or excrement contamination of bite wounds
(e.g., ticks, mosquitoes, kissing bugs). Other
arthropods such as lice or mites cause disease
directly through living and growing in or on the
skin or hair of their host (infestation). Finally,
some arthropods affect humans by injecting
venom during a bite (e.g., spiders, scorpions).
PATHOGENESIS AND CLINICAL
SYMPTOMS
There are two mechanisms through which arthropods
may cause clinical symptoms to occur.
Patients who have been bitten by or infested with
arthropods may exhibit symptoms related solely
to the bite itself or the presence of these arthropods.
In addition to these symptoms, patients
who contract a disease from the arthropod will
also present with symptoms relating to the invasion
of the specific pathogenic microorganism
transferred by the arthropod to the human.
Because the clinical symptoms for each parasite
studied have been noted in earlier chapters, only
those symptoms associated with the arthropod
itself will be discussed in this chapter.