Clinical_Parasitology,_A_Practical-16-26.pptx

1. 1
Copyright © 2013 by Saunders, an imprint of Elsevier Inc.
C H A PTE R
1
Introduction
Elizabeth Zeibig
L E A R N I N G O B J E C T I V E S
On completion of this chapter, the successful
learner will:
1-1. Define each of the following key terms and
phrases:
Accidental or incidental host (pl., hosts)
Animalia
Arthropod (pl., arthropods)
Artifact (pl., artifacts)
Carrier (pl., carriers)
Commensal
Commensalism
Confuser (pl., confusers)
Definitive host
Diagnostic stage (pl., stages)
Disease
Ectoparasite
Elephantiasis
Endoparasite
Epidemiology
Facultative parasite
Helminth (pl., helminthes or helminths)
Host (pl., hosts)
Infection
Infective stage
Infestation
Intermediate host (pl., hosts)
Metazoa
Micron (abbreviated as µ or µm;
pl., microns)
Mode of transmission (pl., modes of
transmission)
Mutualism
Obligatory parasite
O&P
Parasite (pl., parasites)
Parasitic
Parasitic life cycle
Parasitology
Parasitism
Pathogenic
Protozoa
Reservoir host
Symbiosis
Transport host
Vector (pl., vectors)
1-2. Identify and summarize the key discoveries
that have contributed to current knowledge
about parasites.
1-3. Select the areas in the world in which
parasitic infections are endemic and
the factors that contribute to their
occurrence.
W H A T ’ S A H E A D
Focusing In
Historical Perspective
Epidemiology
Parasite-Host Relationships
Parasitic Life Cycles
Disease Processes and
Symptoms
Treatment
Prevention and
Control
Specimen Processing and
Laboratory Diagnosis
Parasite Nomenclature and
Classification
Looking Back

2. CHAPTER 1 Introduction
2
1-17. Summarize, in general terms, the
components of the ova and parasite (O&P)
traditional parasite processing technique
performed on a variety of samples including
stool.
1-18. Give examples of newer parasite recovery
techniques.
1-19. State the name of each of the three
major groups of the clinically significant
parasites.
1-20. Differentiate Protozoa, Metazoa, and
Animalia in terms of definition and the
members of each group.
1-21. Analyze case studies with information
pertinent to this chapter, and:
A. Interpret and explain the information,
data and results provided.
B. Define and explain the parasite-
associated terms and processes
associated with the case.
C. Construct a generic parasite life
cycle.
D. Determine possible parasite-associated
epidemiology, generic, symptoms
and disease processes, treatment,
and prevention and control
measures.
E. Explain the parasite-related processes
going on in the case.
F. Propose subsequent actions to
be taken and/or solutions, with
justification.
G. Design an informational brochure that
contains generic information about all
or select aspects of parasites.
1-4. Identify and describe the main factors
that account for the increased prevalence
of parasites in nonendemic areas of
the world.
1-5. Choose populations of people at risk of
contracting a parasitic infection.
1-6. Identify and describe the primary modes of
parasitic transmission.
1-7. State the primary function of a host in a
parasite-host relationship.
1-8. Explain, in general terms, the parasite-host
relationship.
1-9. Give an example of a parasite defense
mechanism that serves to protect it from a
host’s immune system.
1-10. State the two common phases in the
parasitic life cycle and the significance
of each.
1-11. Identify and describe the key pieces of
information that may be extracted from
each of the two common phases in the
parasitic life cycle.
1-12. List the major body areas that may be
affected as the result of a parasitic
infection.
1-13. Name the most commonly observed
symptoms associated with parasitic
infections.
1-14. Cite examples of available treatment
therapies to combat parasitic
infections.
1-15. Outline possible parasite prevention and
control strategies.
1-16. Select the most commonly submitted
specimen type for parasitic study.
CASE STUDY 1-1 UNDER THE MICROSCOPE
Joe, a third-year medical student, presented to his physi- 2. Indicate where Joe might have come into contact with
cian complaining of severe diarrhea and abdominal pain parasites and identify the factors that likely
contributed and cramping. Patient history revealed that Joe recently to this contact.
(Objective 1-21D)
returned home after a 3-month medical missionary trip to 3. Name two other populations that are at risk of contract-
Haiti. Suspecting that Joe might be suffering from a para- ing parasitic infections. (Objective
1-21D)
sitic infection, his physician ordered a battery of tests, 4. Name two other symptoms associated with parasitic
including a stool sample for parasite examination using a infections that individuals like Joe may experience.
traditional O&P technique. (Objective 1-21D)
Questions and Issues for Consideration 5. What are the key components of a traditional O&P
1. What is a parasite? (Objective 1-21B) examination? (Objective 1-21B)

3. 3
CHAPTER 1 Introduction
important. Advances in other areas of medical
and biologic science, coupled with the discovery
of useful tools, such as microscopes, not only
expanded our knowledge of parasites and their
makeup, but also their relationships with hosts—
that is, plants, animals, and humans known to
harbor parasites.
Today, parasitologists and clinicians have a
wealth of parasite knowledge from which to
draw. The escalation of disease caused by the
presence of parasites (a concept known as para-
sitic) because of global travel tends to result in
higher parasite recovery rates. The increased
number and diversity of these organisms may
allow practitioners to gain high levels of exper-
tise in parasite identification and treatment.
Enhanced preservation of specimens now
allows parasites that otherwise might have been
destroyed to remain viable. A number of advances
in parasitology, particularly in the area of para-
site laboratory diagnosis, promise to be exciting.
Measures are also now in place that are designed
to protect the practitioner when handling samples
for parasite study.
FOCUSING IN
The purpose of this chapter is to introduce the
reader to the study of parasites, organisms that
live on and obtain their nutrients from another
organism, a field known as parasitology. A brief
historical perspective of this field is followed by
an introduction to epidemiology, the factors that
contribute to the frequency and distribution of
parasites, parasite-host relationships, and para-
sitic life cycles, defined as an examination of the
route a parasite follows throughout its life. An
introduction to disease processes and symptoms,
treatment, and prevention and control associated
with parasites are presented. Specifics of these
topics are discussed on an individual parasite
basis, as appropriate. Identification of the three
major groups of clinically significant parasites
follows a section that provides general informa-
tion regarding specimen processing and labora-
tory diagnosis of parasites, covered in more
detail in Chapter 2.
HISTORICAL PERSPECTIVE
The documentation of parasite existence by the
ancient Persians, Egyptians, and Greeks dates
back to prehistoric times. Just as the people of
that era were primitive, relatively speaking, so
too were parasites. Although underdeveloped
areas still exist, humans have progressed through
the years into an age of civilization. Parasites
have evolved as well.
A number of discoveries over the years has
contributed to our current knowledge of parasi-
tology. For example, as increased awareness that
parasites were becoming a problem and the real-
ization that they were responsible for invasion in
the body (infection), invasion on the body (infes-
tation), and disease, defined as a process with
characteristic symptoms, emerged, determining
an effective means of healing infected persons
became a priority. As more information was dis-
covered regarding parasitic life cycles, especially
the fact that transport carriers known as vectors
were frequently responsible for transmission,
parasite control and elimination also became
Quick Quiz! 1-1
Which of the following are key discoveries that
contributed to current knowledge about parasites?
(Objective 1-2)
A. Consistent status quo preservation of samples
B. Techniques that indicate only the presence or
absence of parasites
C. Modifications of traditional parasite identification
techniques
D. Decrease in parasite incidence because of global
travel
EPIDEMIOLOGY
Even though treatment, prevention, and control
measures are available, parasitic infections still
occur and thus it is important to study
and monitor their trends, a field known as epi-
demiology. Although they are distributed world-
wide, most parasitic infections are found in

4. CHAPTER 1 Introduction
4
on to an uninfected host, most often via a blood
meal (bite). Still others will drill their way
into the body via the skin through an unpro-
tected bare foot or when an unsuspecting human
is swimming in contaminated water. Sexual
transmission, mouth-to-mouth contact through
kissing, droplet contamination, and eye contact
with infected swimming water also serve as
routes for parasite transmission.
underdeveloped tropical and subtropical coun-
tries such as Haiti, Guatemala, and Myanmar
(Burma) and countries on the African continent.
Increased population density, poor sanitation,
marginal water sources, poor public health prac-
tices, and environmental changes affecting vector
breeding areas account for the prevalence of para-
sites. The habits and customs of the people living
in these regions are also contributing factors.
The increased prevalence of global travel
likely accounts for parasitic infections being
spread to areas other than where these infections
originated. Individuals who travel to endemic
areas are at risk of contracting parasitic infec-
tions. Refugees, immigrants, and foreign visitors
may bring parasites with them when entering a
nonendemic area.
Representative additional human populations
at risk of contracting a parasitic infection are
listed in Box 1-1. Historically, a dramatic increase
in parasite infection incidence occurred in the
homosexual population but it is now also occur-
ring more in the heterosexual population. More
recently, parasitic infections have become more
prevalent in underdeveloped countries, regard-
less of a person’s sexual orientation.
The means whereby a parasite gains entry into
an unsuspecting host, referred to as mode of
transmission, vary by specific parasite species
and those associated with the parasites covered
in this text are summarized in Box 1-2. Consum-
ing contaminated food or water and hand-to-
mouth transfer are common ways of transmitting
select parasites. Others require an insect (arthro-
pod) vector through which a parasite is passed
BOX 1-1 Populations at Risk for
Contracting Parasites
Individuals in underdeveloped areas and countries
Refugees
Immigrants
Visitors from foreign countries
Individuals who areimmunocompromised
Individuals living in close quarters (e.g.,prisons)
Children who attend day care centers
BOX 1-2 Modes of Parasite Transmission
Ingestion of contaminated food or drink (primarily water)
Hand-to-mouth transfer
Insect bite
Entry via drilling through the
skin Unprotected sexual
relations Mouth-to-mouth
contact
Droplet contamination
Eye contact with infected swimming water
Quick Quiz! 1-2
Which of the following people may be at risk for
contracting a parasitic infection? (Objective 1-5)
A. A toddler who attends an all-day preschool or day
care center
B. A 25-year-old man who lives on his own in an
apartment complex
C. A 37-year-old South American refugee
D. More than one of these:
(specify)
PARASITE-HOST RELATIONSHIPS
The study of parasite-host relationships is over
100 years old. The main focus of this research
has been threefold: (1) recognition of these rela-
tionships; (2) search for patterns of the relation-
ships; and (3) development of methodologies to
study these patterns. Table 1-1 lists the terms
associated with parasite-host relationships, along
with their definitions.
There are several types of parasites that may
be members of a parasite-host relationship. An

5. 5
CHAPTER 1 Introduction
the host’s immune system. Parasites alter their
antigenic makeup so that the host will not reco-
gnize the modified parasites as foreign, and thus
the initiation of an immune response does not
occur. A more in-depth study of parasite-host
relationships is beyond the scope of this chapter.
Where appropriate, further consideration of this
topic is discussed on an individual parasite basis.
organism may be an obligatory parasite or a
facultative parasite. It may be an endoparasite or
an ectoparasite. In the same manner, a number
of different hosts may be part of this parasite-
host relationship. These include accidental or
incidental hosts, definitive hosts, intermediate
hosts, reservoir hosts, transport hosts, and
carriers.
When a parasite infects a host, symbiosis
results. The primary function of the host is to
carry on the parasite’s life cycle. This newly
formed relationship may develop into commen-
salism, mutualism, or parasitism. Some of these
associations exist as commensal under certain
circumstances and pathogenic under others.
Parasites have an amazing capability to adapt
to their host surroundings. In addition to a
number of morphologic adaptations, parasites
are capable of protecting themselves from
Quick Quiz! 1-3
The primary function of a host in a parasite-host
relationship is to: (Objective 1-7)
A. Carry on the parasite’s life cycle.
B. Provide immunologic protection for the host.
C. Carry on the host’s life cycle.
D. Provide a food source for the host.
TABLE 1-1 Terms Associated with Parasite-Host Relationships
Parameter Definition or Description
Type of Parasite
Obligatory parasite Parasite that cannot survive outside of a host
Facultative parasite Parasite that is capable of existing independently of a host
Endoparasite Parasite that is established inside of a host
Ectoparasite Parasite that is established in or on the exterior surface of a host
Type of Host
Accidental or incidental
host
Host other than the normal one that is harboring a parasite
Definitive host Host in which the adult sexual phase of parasite development occurs
Intermediate host Host in which the larval asexual phase of parasite development occurs
Reservoir host Host harboring parasites that are parasitic for humans and from which humans may
become infected
Transport host Host responsible for transferring a parasite from one location to another
Carrier Parasite-harboring host that is not exhibiting any clinical symptoms but can infect
others
Parasite-Host Relationship Terms
Symbiosis Living together; the association of two living organisms, each of a different species
Commensalism Association of two different species of organisms that is beneficial to one and neutral to
the other
Mutualism Association of two different species of organisms that is beneficial to both
Parasitism Association of two different species of organisms that is beneficial to one at the other’s
expense
Commensal Relatingto commensalism; theassociation betweentwo different organisms in which
one benefits and has a neutral effect on the other
Pathogenic Parasite that has demonstrated the ability to cause disease

6. CHAPTER 1 Introduction
6
A parasitic life cycle consists of two common
phases (Fig. 1-1). One phase involves the route a
parasite follows when in or on the human body.
This information provides an understanding of
the symptomatology and pathology of the para-
site. Insights about the best the method of diag-
nosis and selection of appropriate antiparasitic
medication may also be determined. The other
phase, the route a parasite follows independently
of the human body, provides crucial information
pertinent to epidemiology,prevention,and control.
PARASITIC LIFE CYCLES
Although parasitic life cycles range from simple
to complex, they all have three common
components—a mode of transmission, a mor-
phologic form that invades humans, known as
the infective stage, and one (or more) forms that
can be detected via laboratory retrieval methods,
known as the diagnostic stage. Some parasites
require only a definitive host, whereas others also
require one or more intermediate hosts.
= Human = Food
FIGURE 1-1 Generic parasite life cycle.
+
Parasites
come in contact
with human
+
Parasites enter
and establish residence
in or on human
[Infective stage(s)]
Parasites multiply
and compete with
human for
nutritional needs
Parasites emerge
from human
(diagnostic stages)
Parasites
enter outside
environment
Key
= Parasite = Water = Representative
intern host
= Morphologic changes
occur as appropriate
Parasites come
in contact with
soil or water,
intermediate
food hosts
Parasites emerge
from water, food, soil,
intermediate hosts

7. 7
CHAPTER 1 Introduction
BOX 1-3 Symptoms Associated with
Parasitic Disease Processes
Diarrhe
a Fever
Chills
Abdominal pain
Abdominal
cramping
Elephantiasis
Anemia
Vitamin
deficiency
Bowel
obstruction
Edema
Enlargement of major
organs Skin lesions
Blindness
BOX 1-4 Parasite Treatment Options
Antiparasitic
medications Change
in diet
Vitamin
supplements
Fluid
replacement
Blood transfusion
Bed rest
Quick Quiz! 1-4
Which of the following key pieces of information may
be extracted from the portion of a parasite’s life cycle
that occurs outside the body? (Objective 1-11)
A. Parasitic disease symptoms and disease processes
B. Epidemiology and prevention and control
measures
C. Appropriate parasite diagnosis methodologies
D. Selection of appropriate antiparasitic medication
DISEASE PROCESSES
AND SYMPTOMS
A parasitic disease may affect the entire body or
any of its parts. The major body areas associated
with such processes include the following: (1) the
gastrointestinal (GI) and urogenital (UG) tracts;
(2) blood and tissue; (3) liver, lung, and other
major organs; and (4) miscellaneous locations,
such as cerebrospinal fluid (CSF), eye, skin, and
extremities.
A wide variety of representative symptoms,
summarized in Box 1-3, may occur when a para-
site infects a human host. Some persons remain
asymptomatic, whereas other parasites produce
severe symptoms and may result in death. The
most commonly observed symptoms include
diarrhea, fever, chills, abdominal pain, and
abdominal cramping. Other symptoms, such as
elephantiasis (an enlargement of areas such as
the breast, leg, and scrotum caused by a para-
site’s presence), anemia, vitamin deficiency, bowel
obstruction, edema, enlargement of major organs,
skin lesions, and blindness, may develop.
Quick Quiz! 1-5
Which of the following groups of symptoms repre-
sents those most commonly observed in parasitic
infections? (Objective 1-13)
A. Diarrhea, abdominal cramping, and anemia
B. Enlargement of the spleen, fever, and chills
C. Skin lesions, abdominal pain, and diarrhea
D. Abdominal cramping, abdominal pain, and
diarrhea
TREATMENT
There are several options for treating parasitic
infections. Examples of such measures are listed
in Box 1-4. There are a variety of antiparasitic
medications available. Many of these drugs are
toxic to the host and care should be exercised
when selecting the proper course of treatment.
Therapies such as a change in diet, vitamin
supplements, fluid replacement, blood transfu-
sion, and bed rest may be indicated solely or in
addition to chemotherapy. Treatment for non-
pathogenic parasitic infections is usually not
indicated.

8. CHAPTER 1 Introduction
8
SPECIMEN PROCESSING AND
LABORATORY DIAGNOSIS
Proper specimen selection and processing are
crucial to parasite recovery. There are a variety
of acceptable specimen types that may be exam-
ined for parasites. Stool is the most commonly
submitted sample for such studies. Typical stool
analysis consists of performing macroscopic and
microscopic techniques on a portion of unpre-
served sample when available. A process to
remove fecal debris, which often resembles
parasitic forms, is performed on a portion of
sample after a preservative is added to it. Micro-
scopic analysis of the resultant processed
sample follows. This traditional parasite recov-
ery method, often referred to as an O&P, in
which “ O ” stands for ova (eggs) and “P” stands
for parasites, is still widely used today.
Other specimens, including blood, tissue biop-
sies, CSF, sputum, urine, and genital material,
may also be examined for the presence of para-
sites. In some cases, the sample is basically pro-
cessed the same as for stool. Other specimens,
such as blood, are traditionally processed differ-
ently. For example, a Giemsa stain followed by
microscopic examination is the procedure of
choice for blood samples submitted for parasite
study.
A number of other traditional and new para-
site recovery techniques are available. Cello-
phane tape preparation, a methodology for
recovery of pinworm eggs, and the Enterotest
(string test) for recovery of several parasites are
PREVENTION AND CONTROL
Prevention and control measures may be taken
against every parasite infective to humans. Pre-
ventive measures designed to break the transmis-
sion cycle are crucial for successful parasite
eradication. Examples of such measures are listed
in Box 1-5 and include the following: education
programs, use of insecticides and other chemi-
cals, protective clothing, protective netting,
proper water treatment, good personal hygiene,
proper sanitation practices, proper handling and
preparation of food, and avoidance of unpro-
tected sexual relations. The vast capital expendi-
tures required to accomplish these measures are
not available in many endemic countries in the
world. The problem of eradicating parasites is an
ongoing process and is a key goal of interna-
tional health groups such as the World Health
Organization (WHO) and Doctors Without
Borders (Médecins Sans Frontières [MSF]).
BOX 1-5 Parasite Prevention and
Control Strategies
Development and implementation of parasite awareness
education programs
Use of insecticides and other
chemicals Use of protective
clothing
Use of protective
netting Proper water
treatment Good
personal hygiene
Proper sanitation
practices
Proper handling,cooking,and protection of food
Avoidance of unprotected sexual relations
Quick Quiz! 1-6
Which of the following represent examples of avail-
able treatment therapies to combat parasitic infec-
tions? (Objective 1-14)
A. Regulated exercise plan
B. Change in diet
C. Avoidance of vitamin supplements
D. More than one of these: (specify)
Quick Quiz! 1-7
Which of the following are examples of possible
parasite prevention and control measures?
(Objective 1-15)
A. Avoiding the use of insecticides
B. Practicing unprotected sex
C. Practicing proper sanitation practices
D. More than one of these:
(specify)

9. 9
CHAPTER 1 Introduction
nuclear structures, although very different on
further inspection, may often initially appear
almost identical. Plant cells, as another example,
resemble the Ascaris lumbricoides egg (see
Chapter 8 for details), a member of the subking-
dom Metazoa, which includes multicellular
organisms such as parasitic worms. Not only do
they share structural similarities, but both may
measure in the diameter range of 30 to 50 µm.
There are numerous artifacts and confusers (also
often referred to as pseudoparasites) that may be
present in samples submitted for parasite study.
Brief detailed descriptions of a select group of
commonly encountered artifacts and confusers
are discussed in Chapter 12.
among the traditional tests. Representative newer
methodologies are listed in Box 1-6. Details
regarding these various specimen processing
techniques are found in Chapter 2, “Specimen
Collection and Processing.” It is important to
note that Chapter 2 was designed to provide
representative examples of laboratory method-
ologies that may be used to recover parasites.
In some cases, Chapter 2 contains laboratory
methodologies that are not covered in the cor-
responding individual parasite laboratory diag-
nosis sections. Similarly, the laboratory diagnosis
section of select individual parasites mentions
additional possible laboratory techniques that
are not specifically identified as being associated
with these parasites or are not mentioned at all
in Chapter 2. Thus, examination and study of
the methods covered in Chapter 2 and those
identified in the individual parasite laboratory
diagnosis sections are required to understand
and appreciate fully the extent of laboratory
techniques available.
Careful and thorough microscopic examina-
tion of samples for parasites is essential to ensure
that accurate patient results are obtained and
ultimately reported. Suspicious forms that visu-
ally resemble parasites in terms of size and mor-
phology are commonly encountered and are
often referred to as artifacts and/or confusers.
For example, the Entamoeba histolytica cyst
(described in detail in Chapter 3), a single-celled
eukaryotic animal known as a protozoa, typi-
cally measures 12 to 18 microns (µm), a mea-
surement defined as one millionth of a meter
(10−6
m). Similarly, polymorphonuclear leuko-
cytes average 15 µm in size. In addition, the
BOX 1-6 Newer Parasite Laboratory
Diagnosis Techniques
Direct fluorescent antibody
(DFA) Enzyme immunoassay
(EIA) Indirect fluorescent
antibody (IFA) Latex
agglutination (LA)
Polymerase chain reaction
(PCR)
Rapid immunochromatography technique
Quick Quiz! 1-8
Which of the following specimen type is most often
submitted for parasite study? (Objective 1-16)
A. Blood
B. Sputum
C. Urine
D. Stool
PARASITE NOMENCLATURE AND
CLASSIFICATION
The scientific names of parasites are written in
italics and consist of two components, genus (pl.,
genera) and species. An example of a parasite
name is Giardia intestinalis (covered in detail
in Chapter 4), in which Giardia is the genus
name and intestinalis is the species name. When
a parasite name first appears in a document, the
entire parasite name is written out. Subsequent
references to a parasite are often abbreviated
by recording only the first letter of the genera
name followed by a period, followed by the
entire species name. Thus, the abbreviation of
our example parasite Giardia intestinalis is
G . intestinalis.
Variations of scientific genus names are used
to identify diseases and conditions associated
with their presence. The suffix -iasis is often used
to denote such diseases or conditions. For
example, giardiasis refers to the disease or

10. CHAPTER 1 Introduction
10
amebas (Chapter 3). When appropriate, refer-
ence to the amebas may be written in several
ways, such as amebic or ameboid.
There are several different parasite classifica-
tion systems, ranging from very basic to complex.
The system used in this text delineates three
major groups of clinically significant parasites:
1. Single-celled parasites—Protozoa (Fig. 1-2)
2. Multicellular worms—Metazoa helminths
(Fig. 1-3)
3. Arthropods (insects and their allies)—Anima-
lia (Fig. 1-4)
condition associated with Giardia intestinalis. In
some cases, a variation of a scientific genus name
may be used to refer to a genus of parasites. Here
is an example of this use of a genus name.
Chapter 5 of this text discusses two genera of
parasites, Leishmania and Trypanosoma. In
general, reference to infections with these two
genera is often written as leishmanial infections
and trypanosomal infections.
Along with specific parasite name variations,
variations of parasite category names are
common. An example of this terminology is the
FIGURE 1-2 Parasite classification—the protozoa.
Subkingdom
Protozoa
Phylum
Sarcomastigophora
Subphylum
Mastigophora
Phylum
Ciliophora
Phylum
Apicomplexa
Order
Blastocystida
Subphylum Class
Sarcodina Lobosea (amebas)
Class
Zoomastigophora
(flagellates/hemoflagellates)
Class
Kinetofragminophorea
(ciliates)
Class
Blastocystea
Class
Sporozoa
Species
See Chapter 2
Species
See Chapters 3 and 4
Species
See Chapters 5 and 6
Species
See Chapter 6
Species
See Chapter 6
FIGURE 1-3 Parasite classification—the helminths.
Subkingdom
Metazoa
Phylum
Nemathelminthes
Phylum
Platyhelminthes
Class
Nematoda
(roundworms)
Class
Filariae
(tissue roundworms)
Class
Cestoda
(tapeworms)
Class
Trematoda
(flukes)
Species
See Chapter 7
Species
See Chapter 8
Species
See Chapter 9
Species
See Chapter 10

11. 11
CHAPTER 1 Introduction
The groups of parasites in each classification
table are organized by kingdom and subking-
dom, phylum and subphylum, and class. The
individual species are classified in their respective
chapters.
Kingdom
Animalia
Phylum
Arthropoda
Class
Crustacea
(crabs, crayfish, etc.)
Class
Arachnida
(ticks, mites, etc.)
Class
Insecta
(insects)
Class
Chilopoda
(centipedes)
Class
Pentastomida
(tongueworms)
FIGURE 1-4 Parasite classification—the arthropods.
Species
See Chapter 12
Species
See Chapter 12
Quick Quiz! 1-9
Which of the following correctly represents the three
major groups of clinically significant parasites? (Objec-
tive 1-20)
A. Protozoa—worms; Metazoa—single-celled para-
sites; Arthropods—insects and their allies
B. Protozoa—insects and their allies; Metazoa—
worms; Arthropods—single-celled parasites
C. Protozoa—single-celled parasites; Metazoa—
worms; Arthropods—insects and their allies
D. Protozoa—single-celled parasites; Metazoa—
insects and their allies; Arthropods—worms
LOOKING BACK
Over the years, parasites once considered com-
mensal have evolved to become human patho-
gens. During thistime, wehavegained tremendous
knowledge of the epidemiology, parasite-host
relationships, life cycles, disease processes and
symptoms, treatment, and prevention and control
Column A Column B
A. Ectoparasite 1. The form of a
parasite that
enters a host
B. Obligatory
parasite
2. Two organisms of
different species
living together
of parasites. In addition, parasites are classified
based on their individual characteristics. Tradi-
tional as well as new methodologies for parasite
identification allow for accurate laboratory
diagnosis.
Parasitology is an interesting and exciting field
of the clinical laboratory sciences. The continued
development of high-tech, highly sensitive para-
site test methodologies provides the key to the
future of parasitology. Because it is highly
unlikely that parasites will totally be eradicated
in the near future, competent practitioners edu-
cated in the field of parasitology are essential to
ensure proper parasite identification.
TEST YOUR KNOWLEDGE!
1-1. Match each of the key terms (column A)
with its corresponding definition (column
B). (Objective 1-1)