The Protozoa
Blood & Tissue Protozoa
The Hemoflagellates:
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The family Trypanosomatidae contains only two genera
that parasitize humans.
Genus Trypanosoma contains members that may be
found either in the circulating blood or intracellularly (in
cardiac muscle). African - blood; American - blood &
cardiac muscle.
Genus Leishmania are always intracellular, principally in
cells of the reticuloendothelial system.
The Protozoa
Blood & Tissue Protozoa
The Hemoflagellates:
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Originally parasites of insects;
these now serve as
intermediate hosts.
American trypanosomiasis transmitted by reduviid bugs.
African trypanosomiasis transmitted by Glossina spp.
tsetse flies.
The Protozoa
Blood & Tissue Protozoa
The Hemoflagellates:
 "Old World” leishmaniasis transmitted Phlebotomus spp.
sandflies.
 American leishmaniasis transmitted by Lutzomyia spp.
sandflies.
The Protozoa
The Hemoflagellates:
Trypanosoma b. rhodesiense
Trypanosoma b. gambiense
Trypanosoma brucei
 Two subspecies: rhodesiense &
gambiense
 Life cycles are essentially identical.
 Rhodesian form - primarily an animal
pathogen, transmitted to humans by
Glossina morsitans.
 Gambian form - transmitted by Glossina
palpalis group of tsetse fly.
The Protozoa
The Hemoflagellates:
Trypanosoma brucei (both sub-species)
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Site of infection - organisms multiply in blood early in disease;
later found in lymph nodes and in the CNS.
Disease - febrile episodes, night sweats, malaise, headache;
enlarged cervical lymph nodes (“Winterbottom’s sign”); final
stages - uncontrolled desire to sleep.
Diagnosis - examine wet mounts of aspirates from sight of insect
bite; and/or blood (buffy coat) for presence of trypanosomes
(numbers of organisms peak during fever spikes).
Morphology - Epimastigote is the developmental form in flies;
trypomastigote is the infective stage.
The Protozoa
The Hemoflagellates:
Trypanosoma cruzi
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Disease - American trypanosomiasis, Chagas'
disease.
Transmission - trypomastigote in reduviid bug
feces is introduced through the skin following
the bug's bite.
Morphology - exhibits a characteristic “C”
shape with an undulating membrane and
anteriorly extending flagellum; the amastigote
is oval, averages 3 to 5 microns in diameter
and contains a nucleus and rod-shaped
kinetoplast.
The Protozoa
The Hemoflagellates:
Trypanosoma cruzi
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Trypomastigote and epimastigote forms may be found
in humans. The amastigote is a tissue stage; the
trypomastigote is blood stage; the epimastigote is a
developmental stage in the bug.
Pathogenesis - acute phase is 1- 4 month’s duration;
chronic phase may last decades.
Clinical signs - Edema of eyelids (Romana’s sign).
Fever, headache, malaise, myalgia, megacolon,
megaesophagus. Cardiac manifestations.
The Protozoa
The Hemoflagellates:
Trypanosoma cruzi
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Epidemiology notes: most prevalent in South America
especially Brazil, Argentina, Uruguay, Chile, and
Venezuela. Has been found in Central America. Five
cases have been confirmed in Texas; one in California.
There is great concern about transfusion-induced cases
in the blood banking industry.
Reservoir hosts - many animals including dogs,
opossums, cat, armadillos, etc.
The Protozoa
The Hemoflagellates:
Genus Leishmania
Four pathogenic species.
 Speciation - based on clinical
symptoms and manifestations.
 Diagnosis - finding amastigotes
in lesions; clinical signs and
symptoms determine the
“differential” diagnosis.
The Protozoa
The Hemoflagellates:
Leishmania tropica
 Distribution - Mediterranean
basin, India, Middle East, Asia &
Africa.
 Disease - Old World cutaneous
leishmaniasis; “Baghdad boil,”
“Oriental sore.”
 Diagnosis - identification of
intracellular amastigotes in
macrophages from active lesions.
The Protozoa
The Hemoflagellates:
Leishmania tropica
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Moist ulcers - Incubation period of several
weeks to months, followed by rapid
development of weeping ulcers that heal
within 6 months.
Dry ulcers - Incubation period may last for
several years before appearance of a slowly
developing ulcer that is covered with a scaly
crust. May take years to heal.
Healing of lesions of cutaneous
leishmaniasis signifies cell-mediated,
species-specific, lifelong immunity.
The Protozoa
The Hemoflagellates:
Leishmania mexicana
 Similar to L. tropica in that it causes cutaneous
leishmaniasis. Found in Central America,
Mexico, & Texas.
 Disease - New World cutaneous leishmaniasis,
chiclero ulcer.
 Diagnosis - identification of amastigotes at
periphery of lesion. Necrotic area at center of
lesion contains bacteria, few if any organisms.
The Protozoa
The Hemoflagellates:
Leishmania braziliensis
 Disease - Mucocutaneous
leishmaniasis, espundia.
 Disfigurement - erosion of oral,
nasal structures. Affects mainly
the mucous membranes and
cartilaginous areas of the nasal
and oral structures.
The Protozoa
The Hemoflagellates:
Leishmania donovani
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Disease - visceral leishmaniasis,
kala-azar (“black fever”).
Pathogenesis - a viscerotropic
form, skin lesion seldom noticed;
in reticuloendothelial system,
organisms multiply; extensive
hyperplasia of parasitized tissue
impairs function of organs.
The Protozoa
Miscellaneous Others:
Toxoplasma gondii
 Definitive host - felines, domestic
cat is most important.
 Human infections are due to
ingestion of infective oocysts from
cat feces; ingestion of trophozoites
in undercooked or uncooked meat,
mother’s milk; congenital
transmission has been documented.
The Protozoa
Miscellaneous Others:
Toxoplasma gondii
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Infections are usually asymptomatic;
immune system keeps infection in
check; immunosuppression (HIV, etc.)
results in fulminating infection.
Dangerous in pregnant women - the
organism can cross the placental
barrier and infect the fetus.
Diagnosis - isolation of organism is
difficult; best diagnosed via
serological techniques.
The Protozoa
Miscellaneous Others:
Babesia spp.
 A widespread zoonosis,
transmitted via the bite of
infected hard ticks.
 Sexual reproduction takes place
in ticks. Asexual reproduction
takes place in a variety of
mammalian hosts.
The Protozoa
Miscellaneous Others:
Babesia spp.
 Multiplies within red blood cells; can
be confused with malaria ring forms.
Babesia rings are more pyriform,
multiplication results in pairs and
tetrads resembling a “maltese cross.”
 Pathology - Hemolysis is common,
resulting in anemia and jaundice.
Severe cases progress to renal
failure, hypotension, coma and death.
The Protozoa
Miscellaneous Others:
Pneumocystis carinii
 Classification of the organism is
uncertain (fungus or parasite).
 Pathology - “Interstitial Plasma-Cell
Pneumonia,” a highly fatal complication
of AIDS. The organism and infection are
widespread, similar to toxoplasmosis.
 Diagnosis - identification of cysts
(containing 8 trophozoites) or free
trophozoite forms in lung exudates;
sputum (AIDS patients); open lung
biopsy, bronchio-alviolar lavage (BAL).