The Hemoflagellates

MORPHOLOGY AND LIFE
CYCLE NOTES
Morphology
Amastigotes. The average roundish to oval
amastigote measures 5 by 3 ?m in size (Figs. 5-1
and 5-2; Table 5-1). The amastigote contains a
nucleus, a basal body structure (called a blepharoplast),
and a small parabasal body. The large
single nucleus is typically located off-center,
sometimes present more toward the edge of the
CASE STUDY 5-1 UNDER THE MICROSCOPE
Nine-year-old Charles, an African boy, recently emigrated
to the United States from Kenya with his family. He began
complaining of chills and diarrhea 2 weeks prior to the
office visit. After taking his temperature, which revealed a
fever, his mother took him into his pediatrician’s office.
During the examination, the doctor found a skin lesion on
his right arm and marked hepatosplenomegaly. A complete
blood count (CBC) was ordered, which revealed that
Charles was anemic. The doctor, afraid that the child
was experiencing dum dum fever (kala-azar), ordered
a biopsy of the infected skin lesion and blood for
parasite study.
When the specimens were received in the laboratory,
the laboratory technician on duty made slides of the skin
lesion material and blood, stained them with Giemsa stain,
and carefully examined the slides. No parasites were found
in the blood slide. The biopsy slide revealed an oval organism
(see diagram); it contained one nucleus, a parabasal
body, and an axoneme-like structure.
Questions for Consideration
1. What parasite do you suspect? (Objective 5-10B)
2. Which morphologic form of the parasite was described
in the biopsy slide? (Objective 5-10B)
3. Indicate where Charles might have come into contact
with parasites and identify the factors that most likely
contributed to this contact. (Objectives 5-10D)
4. Name two other geographic populations at risk of contracting
parasitic infections. (Objectives 5-10D)
5. Name two other symptoms associated with parasitic
infections that individuals such as the patient in this
case study may experience. (Objective 5-10C)
6. Why did the physician additionally order blood to be
examined for parasites? (Objectives 5-10F)
CHAPTER 5 The Hemoflagellates 107
organism. The dotlike blepharoplast gives rise to
and is attached to an axoneme. The axoneme
extends to the edge of the organism. The single
parabasal body is located adjacent to the blepharoplast.
Kinetoplast is an umbrella term often
used to refer to the blepharoplast and small parabasal
body.
Promastigotes. The typical promastigote measures
9 to 15 ?m in length (Figs. 5-3; Table 5-2).
The large single nucleus is located in or near the
center of the long slender body. The kinetoplast
is located in the anterior end of the organism. A
single free flagellum extends anteriorly from the
axoneme.
Epimastigotes. The average epimastigote measures
approximately 9 to 15 ?m in length (Fig.
5-4; Table 5-3). The body is slightly wider than
FIGURE 5-1 Amastigote.
Nucleus
Parabasal body
Blepharoplast
Kinetoplast
Axoneme
Average size: 5 m by 3 m
FIGURE 5-2 Amastigotes of Leishmania spp. (From
Mahon CR, Lehman DC, Manuselis G: Textbook of diagnostic
microbiology, ed 4, St Louis, 2011, Saunders.)
Parameter Description
Size 5 by 3 ?m
Shape Round to oval
Nucleus One, usually off center
Other features Kinetoplast present, consisting of
dotlike blepharoplast from
which emerges a small
axoneme
Parabasal body located adjacent
to the blepharoplast
TABLE 5-1 Amastigote: Typical
Characteristics at a Glance
FIGURE 5-3 Promastigote.
Size range: 9-15 m long
Nucleus Parabasal body
Kinetoplast
Flagellum
Anterior end
Axoneme
Posterior end
Blepharoplast
Parameter Description
Size 9-15 ?m long
Appearance Long and slender
Nucleus One, located in or near center
Other features Kinetoplast, located in anterior
end
Single free flagellum, extending
from anterior end
TABLE 5-2 Promastigote: Typical
Characteristics at a Glance
108 CHAPTER 5 The Hemoflagellates
that of the promastigote. The large single nucleus
is located in the posterior end of the organism.
The kinetoplast is located anterior to the nucleus.
An undulating membrane, measuring half the
body length, forms into a free flagellum at the
anterior end of the epimastigote.
Trypomastigotes. The typical trypomastigote
measures 12 to 35 ?m long by 2 to 4 ?m wide,
and may often assume the shape of the letters C,
S or U in stained blood films (Figs. 5-5 to 5-7;
Table 5-4). The trypomastigote in Figure 5-5 is
represented in its straight form for comparison
purposes because it clearly denotes the individual
structures. The long slender organism is characterized
by a posteriorly located kinetoplast from
which emerges a full body length undulating
membrane. The single large nucleus is located
anterior to the kinetoplast. An anterior free flagellum
may or may not be present.
General Morphology and Life
Cycle Notes
The amastigote and trypomastigote are the two
forms routinely found in human specimens.
Amastigotes are found primarily in tissue and
FIGURE 5-4 Epimastigote.
Size range: 9-15 m long
Undulating membrane Flagellum
Anterior end
Kinetoplast
Parabasal body Blepharoplast
Nucleus
Posterior end
Parameter Description
Size 9-15 ?m long
Appearance Long and slightly wider than
promastigote form
Nucleus One, located in posterior end
Other features Kinetoplast located anterior to
the nucleus
Undulating membrane, extending
half of body length
Free flagellum, extending from
anterior end
TABLE 5-3 Epimastigote: Typical
Characteristics at a Glance
FIGURE 5-5 Trypomastigote.
Size range: 12-35 m by 2-4 m
Flagellum
Nucleus Undulating membrane
Posterior end
Axoneme
Blepharoplast
Parabasal body
Anterior end
Kinetoplast
CHAPTER 5 The Hemoflagellates 109
samples, epimastigotes are found primarily in the
arthropod vector. Specific life cycle information
is found under the discussion of each individual
hemoflagellate.
Parameter Description
Size 12-35 ?m long by 2-4 ?m wide
Shape C, S or U shape often seen in
stained blood films
Appearance Long and slender
Nucleus One, located anterior to the
kinetoplast
Other features Kinetoplast located in the posterior
end
Undulating membrane, extending
entire body length
Free flagellum, extending from
anterior end when present
TABLE 5-4 Trypomastigote: Typical
Characteristics at a Glance
FIGURE 5-6 Trypanosoma cruzi trypomastigote exhibiting
a characteristic full body length undulating membrane
(arrow). Note the S shape of the organism (Giemsa stain,
×1000). (Courtesy of WARD’S Natural Science Establishment,
Rochester, NY; http://wardsci.com.)
FIGURE 5-7 Trypanosoma cruzi C-shaped trypomastigote
in a blood smear. (From Mahon CR, Lehman DC,
Manuselis G: Textbook of diagnostic microbiology, ed 4,
St Louis, 2011, Saunders.)
muscle, as well as the central nervous system
(CNS) within macrophages, where they multiply.
Trypomastigotes reproduce and are visible in the
peripheral blood. The promastigote stage may be
seen only if a blood sample is collected immediately
after transmission into a healthy individual
or when the appropriate sample is cultured.
Although they may be seen in human blood
Quick Quiz! 5-1
This is the only hemoflagellate morphologic form
that does not have an external flagellum. (Objective
5-11A)
A. Trypomastigote
B. Amastigote
C. Promastigote
D. Epimastigote
Laboratory Diagnosis
Blood, lymph node and ulcer aspirations, tissue
biopsies, bone marrow, and cerebrospinal fluid
(CSF) are the specimens of choice for diagnosing
the hemoflagellate morphologic forms. In addition,
serologic and molecular tests are also
available for confirming the presence of these
organisms. Representative laboratory diagnosis
methodologies are presented in Chapter 2, as
well as in each individual parasite discussion, as
appropriate.
110 CHAPTER 5 The Hemoflagellates
Pathogenesis and Clinical Symptoms
The symptoms associated with hemoflagellate
infections range from a small red papule at the
infection site, with intense itching, secondary
bacterial infections, fever, and diarrhea, to kidney
involvement, mental retardation, a comatose
state, and death. In some cases, the initial skin
lesions spontaneously heal, whereas in others
they may remain dormant for months or even
years.
have only been known to occur on rare occasions.
A discussion of each of these organisms is
beyond the scope of this chapter. For the purpose
of discussing the Leishmania species, this chapter
will address them within the classification complexes
of more popular texts and literature, as
opposed to the individual species. Only those
hemoflagellates known to cause more frequent
human disease are covered. The individual
species are identified and classified in Figure 5-8.
HISTORICAL PERSPECTIVE OF
LEISHMANIASIS
Leishmaniasis is a general term used to describe
diseases caused by the hemoflagellate genus
Leishmania. Although its origins remain unclear,
what is obvious is that the organisms in this
genus and their respective vectors have made
successful migrations and adaptations to many
environments worldwide. Leishmaniasis has a
long history, as evidenced by the depictions on
pottery from Ecuador and Peru around the first
century AD. The different groups of people
exposed to the organism have provided us with
a number of common names for the diseases
caused by Leishmania spp. (e.g., Baghdad boils,
bay sore, chiclero ulcer, dum dum fever, espundia,
forest yaws, kala-azar, oriental sore, pian
bois, and uta). Table 5-5 describes each of these
conditions. Increased travel and exposure to different
environments has resulted in the transmission
of the various parasitemias, a general term
Quick Quiz! 5-2
Hemoflagellates are typically found in stool samples.
(Objective 5-8)
A. True
B. False
Quick Quiz! 5-3
The symptoms of hemoflagellate infections range
from minor, such as irritation at the infection site, to
serious (comatose state and death). (Objective 5-6)
A. True
B. False
HEMOFLAGELLATE
CLASSIFICATION
There are a number of hemoflagellate species
known to cause human infections, some of which
FIGURE 5-8 Parasite classification—the hemoflagellates.
Subphylum
Mastigophora
Class
Zoomastigophora
Blood Tissue Species
Leishmania braziliensis complex
Leishmania donovani complex
Leishmania mexicana complex
Leishmania tropica complex
Trypanosoma brucei gambiense
Trypanosoma brucei rhodesiense
Trypanosoma cruzi
Trypanosoma rangeli
tahir99-VRG & vip.persianss.ir
CHAPTER 5 The Hemoflagellates 111
describing parasitic infection of the blood, into
new environments, finding new host organisms
and new vectors.
Leishmania spp. are generally grouped for discussion
in one of several ways—in complexes of
organisms or taxonomic groupings, their vectors,
or the clinical nature of the disease caused. The
four main complexes considered and described
herein are the Leishmania braziliensis, Leishmania
donovani, Leishmania mexicana, and Leishmania
tropica complexes.
Leishmania braziliensis complex
(leesh-may’ nee-uh/bra-zil” i-en’sis)
Common associated disease and condition names:
Mucocutaneous leishmaniasis, chiclero ulcer, espundia,
forest yaws, pian bois, uta.
The Leishmania braziliensis complex of organisms
is found in Mexico, Argentina, Panama,
Colombia, the Peruvian Andes, Guiana, Brazil,
Bolivia, Paraguay, Ecuador, and Venezuela. This
group of parasites is comprised of Leishmania
braziliensis, Leishmania panamensis, Leishmania
peruviana, and Leishmania guyanensis. This
leishmanial complex and the diseases for which
its organisms are the causative agent may also be
referred to as New World because of their geographic
location in what is commonly considered
the New World.
Laboratory Diagnosis
The specimen of choice for identifying the amastigotes
of L. braziliensis complex is a biopsy
of the infected ulcer. Microscopic examination of
the Giemsa-stained preparations should reveal
the typical amastigotes. Promastigotes may be
present when the sample is collected immediately
after introduction into the patient. Other more
commonly used diagnostic methods include culturing
the infected material, which often demonstrates
the promastigote stage, and serologic
testing. As enzyme analysis and molecular techniques
have become more widely available,
diagnostic criteria have begun to change as well.
However, restriction analysis of kinetoplast
DNA, a technique referred to as schizodeme
analysis, nuclear DNA hybridization, and isoenzyme
patterns, known as zymodeme analysis,
still tend to remain research procedures and are