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.

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.

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 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

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.

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.

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.

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.

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 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.

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.

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 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 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.

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).