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The Protozoa
Blood & Tissue Protozoa
The Hemoflagellates:
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.
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The Protozoa
Blood & Tissue ProtozoaThe Hemoflagellates:
Originally parasites of insects; these now serve as intermediate hosts.
American trypanosomiasis - transmitted by reduviid bugs.
African trypanosomiasis - transmitted by Glossina spp. tsetse flies.
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The Protozoa
Blood & Tissue Protozoa
The Hemoflagellates: "Old World” leishmaniasis -
transmitted Phlebotomus spp. sandflies.
American leishmaniasis - transmitted by Lutzomyia spp. sandflies.
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The Protozoa
The Hemoflagellates: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.
Trypanosoma b. rhodesiense
Trypanosoma b. gambiense
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The Protozoa
The Hemoflagellates:Trypanosoma brucei (both sub-species) 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.
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The Protozoa
The Hemoflagellates:
Trypanosoma cruzi 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.
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The Protozoa
The Hemoflagellates:Trypanosoma cruzi 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.
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The Protozoa
The Hemoflagellates:
Trypanosoma cruzi 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.
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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.
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The ProtozoaThe 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.
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The Protozoa
The Hemoflagellates:Leishmania tropica 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.
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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.
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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.
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The Protozoa
The Hemoflagellates:
Leishmania donovani 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.
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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.
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The ProtozoaMiscellaneous Others:
Toxoplasma gondii 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.
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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.
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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.
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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).