Medical Protozoology Notes

Medical Protozoology

  • Study plan:
    • Parasite name (Latin)
    • Medical significance (disease caused)
    • Invasive and infection forms
    • Morphological features
    • Life cycle
    • Pathogenic effect (disease clinic)
    • Lab diagnosis

Protozoans

  • Unicellular animals, microscopically small.
  • Cell structure: cytoplasm (ectoplasm + endoplasm), shell (except sarcodes).
  • Endoplasm contains organoids for digestion, excretion, movement (flagella, cilia), protection, photosensitive eye, chromatophores.
  • Heterotrophic, breathe via body surface.
  • Reproduction: asexual or sexual. Nucleus divides by mitosis.
  • Contractile vacuoles protect from excess water.
  • React to external stimuli (taxis): positive or negative.
  • Form cysts under unfavorable conditions.

Classification

  • TYPE OF SARCOMASTIGOPHORA
  • TYPE OF INFUSORIA
  • TYPE OF MACROSPORIDIA

TYPE OF SARCOMASTIGOPHORA

  • SARCODES
  • FLAGELLATES

SARCODES: Entamoeba histolytica

  • Disease: dysentery amoebiasis.
  • Two stages: infectious cyst and trophozoite.
  • Trophozoites: formamagnaforma_magna, formaminutaforma_minuta, tissue.
    • FormamagnaForma_magna (30-40 microns): ingests red blood cells, secretes proteolytic enzymes.
    • Tissue form (20-25 microns): amoeboid movement.
    • FormaminutaForma_minuta (12-20 microns): non-pathogenic, feeds on bacteria.
  • Cyst (8-16 microns): motionless, round, colorless, 4 nuclei.
  • Infection: cysts ingested.
  • Life cycle: cysts ingested → f.minutaf._minuta → cysts again (dangerous to others) or → f.magnaf._magna → tissue form (destroys intestinal wall, ulcers).

Clinical Presentation

  • Asymptomatic: parasites in intestine lumen.
  • Colitis: abdominal cramping, tenderness, weight loss, mucoid/bloody diarrhea.
  • Fulminant necrotizing colitis: rare, high mortality, fever, bloody diarrhea, leukocytosis, peritoneal tenderness; may require surgery.
  • Complication: liver abscesses.

Diagnosis

  • Microscopy of intestinal ulcers: detect large and tissue forms.

FLAGELLATES: African Trypanosomiasis

  • Vector-borne disease caused by Trypanosoma sp.
  • Trypanosoma brucei: acute or chronic, damages central nervous system.
  • Sleeping sickness: fever, edema, enlarged lymph nodes, CNS damage.
  • Two subspecies: Gambian (anthroponosis) and Rhodesian (zoonosis).
  • Distribution: tropical Africa (Glossina morsitans habitat).
  • Transmission: Glossina (tsetse fly) bite; invasive stage is metacyclic trypanosomes.

Cellular Forms

  • Epimastigous: insect intestine.
  • Trypomastigous and amastigous: mammalian body.
  • Amastigous: oval/round, no flagellum.
  • Epimastigous: oblong, kinetoplast at cell back.
  • Trypomastigous: undulating membrane.
  • Metacyclic: no free flagellum (invasive form).

Clinic

  • Early stage: trypanosomal chancre, fever, enlarged lymph nodes/liver/spleen, weakness.
  • Late stage: neuropsychiatric symptoms, drowsiness, muscle weakness, exhaustion, depression, death.

Diagnostics

  • Early: pathogen at bite site, blood (Rhodesian), or lymph node punctate (Gambian).
  • Late: trypanosomes in cerebrospinal fluid.

American Trypanosomiasis (Chagas Disease)

  • Vector-borne infection caused by Trypanosoma cruzi.
  • Vectors: triatomine insects ("kissing bugs").
  • Widespread in Central/South America; chronic infection leads to heart failure.
  • Transmission: contamination by infected bedbug excrement.
  • Invasive stage: metacyclic trypomastigotes.

Life Cycle

  • Parasitizes smooth muscle cells.
  • Metacyclic trypomastigotes → trypomastigotes in bloodstream → amastigotes (divide in cells).

Clinic

  • Acute: fever, chills, malaise, eye/muscle pain, chagoma.
  • Chronic: asymptomatic; "megasyndrome" (enlarged organs).

Diagnostics

  • Acute: blood smear, chancre punctate, lymph nodes.
  • Chronic: immuno-enzyme analysis, bioassay, culture.

FLAGELLATE: Giardia intestinalis

  • Pear-shaped (10-18 microns), 8 flagella, 2 axostyles, suction disc.
  • Cysts: oval/round (10-14 microns), two nuclei.
  • Infection: cysts ingested → trophozoite emerges in duodenum.
  • Symptoms: diarrhea, abdominal cramping, bloating, flatulence, fatigue; greasy/malodorous stools.
  • Transmission: fecal-oral route.
  • Diagnosis: stool examination for trophozoites/cysts.

Leishmaniasis

  • Causative agents: Leishmania.
    • Cutaneous: Leishmania tropica minor/major.
    • New World: Leishmania mexicana, L. peruviana, L. braziliensis.
    • Visceral: Leishmania donovani.
  • Carrier: mosquito Phlebotomus papatasi.

Leishmania Types

  • Leishmania tropica minor: Anthroponous cutaneous leishmaniasis.
  • Leishmania tropica major: Zoonotic cutaneous leishmaniasis.
  • Leishmania mexicana, L. peruviana, L. braziliensis: Severe deformities of nose, auricles, nasopharynx, larynx, and external genitalia
  • Leishmania donovani: Visceral (Kala-Azar), widespread in AFRICA AND SOUTH ASIAN COUNTRIES.

Morphological Features

  • Amastigotes (leishmaniform): immobile, parasitize cells of bone marrow, spleen, liver, skin.
  • Promastigotes (leptomonas): mobile, 1 flagellum, divide longitudinally, develop in mosquito.

Life Cycle

  • Mosquito bite injects flagellated forms → cells of internal organs → leishmanial form (main form).

Cutaneous Leishmaniasis

  • Symptoms: erythematous bumps → ulcer with raised edges (leishmanioma).

New World

  • Symptoms: ulcers, tissue destruction/overgrowth.

Visceral Leishmaniasis (Kala-Azar)

  • Symptoms: fever, weakness, headache, intoxication, skin pigmentation, rash, enlarged liver/spleen, anemia.

Trichomoniasis (Trichomonas vaginalis)

  • Trophozoite form only, divides by binary fission, no cysts, sexually transmitted.
  • Infects lower urinary/reproductive tracts; causes vaginitis/urethritis, itching, burning, green discharge.
  • Diagnosis: trophozoite in discharge smears (long spike, five flagella).

Malaria

  • Apicomplexa: Plasmodium falciparum, P. vivax, P. malariae, P. ovale.
  • Transmission: Anopheles mosquito bite (sporozoites).

Life Cycle

  • Sporozoites → liver (asexual reproduction, tissue schizont, merozoites).
  • Merozoites → red blood cells (erythrocytic stage, asexual development: ring, trophozoite, schizont).
  • Diagnosis: parasites within erythrocytes on blood smears.

Erythrocyte Phase

  • Plasmodium malariae: Seizures after 72 hours. The causative agent of four–day malaria is characterized by the shape of the ribbon
  • Plasmodium vivax, P.ovale: Seizures – after 48 hours the causative agent of three-day malaria is characterized by the shape of a ring.
  • Plasmodium falciparum: paroxysms are acyclic, prolonged, the causative agent of tropical malaria is a form of the half moon.

Malaria Symptoms

  • Incubation: 10-14 days.
  • Symptoms: fever, anemia, circulatory disorders, high temperature, chills/sweats.
  • Complications: cerebral edema, malarial coma, renal failure, mental disorders.
  • Attack phases: chills, fever, sweat.
  • Diagnosis: parasite detection in blood (during attack).

Toxoplasmosis (Toxoplasma gondii)

  • Localization: cells of brain, heart, muscles, eye tissue, lungs, uterine walls.
  • Morphology: merozoites (orange lobule/crescent), conoid, large nucleus.
  • Hosts: cats (main), animals, birds, humans (intermediate).

Life Cycle

  • Oocysts (cat feces), tachyzoites (infect macrophages), tissue cysts (pseudocysts), bradyzoites (in cysts).
  • Tachyzoites infect macrophages → cell disruption, inflammation.
  • Tissue cysts form (brain, muscle) → bradyzoites released if immune system compromised.

Clinical Manifestations

  • 80-90% asymptomatic.
  • Mild symptoms: lymphadenopathy, myalgia, headache, rash, sore throat.
  • Congenital: transmission during pregnancy (new infections).

Congenital Toxoplasmosis

  • New infections more likely to transmit to fetus
  • Severity of disease in the fetus are inversely proportional
  • First trimester higher risk of severe symptoms/death.

Diagnosis

  • Serological tests (recent/past infection) or direct organism detection.