Protozoa Biology Quiz

Medical Protozoology

• Protozoa are microscopic, single-celled organisms capable of all life functions.
• Amoebas have a complex internal structure:
  • Food vacuole
  • Pseudopodia
  • Plasmagel
  • Plasmasol
  • Ectoplasm
  • Endoplasm
  • Uroid
  • Contractile vacuole
  • Water vacuole
• Protozoa have a relatively complex internal structure and carry out complex metabolic activities.
• Protozoa's body consists of:
  • Protoplasm, enclosed by a cell membrane
  • Divided into outer ectoplasm and inner endoplasm,
  • Nucleus, endoplasmic reticulum
  • Food storage granules, contractile and digestive vacuoles.
• The nucleus contains clumped or dispersed chromatin.
• Locomotion by:
  • Pseudopodia (amoebae)
  • Cilia (ciliates)
  • Flagella (flagellates)
  • Undulant movement (sporozoa).

Life Cycle Stages of Protozoa

• Trophozoites: actively feed and multiply.
• Cysts: have a protective membrane, allow protozoa to survive outside the host, usually have resistant walls.

Classification of Protozoa

• Small Intestine: Giardia lamblia
• Large intestine: Entamoeba histolytica
• Blood: Plasmodium species
• Tissue: Toxoplasma gondii
• Urogenital: Trichomonas vaginalis

Nutrition

• Liquid food: Absorption through the body surface.
• Solid particles:
  • Pinocytosis (liquid form)
  • Phagocytosis (using pseudopodia).
  • Cytostome (flagellates or sporozoa, ciliates, amoeba)

Excretion

• Excretion through contractile vacuoles rupturing to outside.
• Some waste products are deposited in cytoplasm.
• In sporozoa, waste is excreted as pigment.

Respiration

• Aerobic: Protozoa living in tissues and blood.
• Anaerobic: Protozoa living in the intestine lumen.

Secretion

• Protozoa secrete digestive ferments, pigments.
• Lytic enzymes help tissue lysis.
• Toxins.
• Cyst walls allow resistance from unfavorable conditions, transfer to other hosts without destruction.

Reproduction

• Asexual reproduction:
  • Simple fission: nucleus and cytoplasm divide into equal parts, forming two cells.
  • Multiple fission: nucleus divides first into several parts, cytoplasm divides forming several small daughter cells.
• Sexual reproduction:
  • Conjugation: exchange of nuclear material between two organisms
  • Gametogony: formation of male and female gametes, their union to form zygote.

Entamoeba histolytica

• Geographical distribution: worldwide, areas with poor sanitation

• Habitat: large intestine (caecum, colonic flexures, sigmoidorectal region).

• Definitive host: Man

• Reservoir host: Dogs, pigs, rats, monkeys

• Infective stage: Mature cyst

• Diagnostic stage: cyst and trophozoite

• Trophozoite Size: 20µm (15-60μm)

• Shape: Irregular

• Cytoplasm: Differentiated into ectoplasm, endoplasm

• Ectoplasm: Clear with a finger-like pseudopodia

• Endoplasm: Granular, with nucleus, karyosome small and central

• Spherical nucleus

• Peripheral chromatin, uniform size, arranged on the inner surface of nuclear membrane

• Food vacuoles: may contain RBCs (no bacteria)

• Mature cyst (Quadrinucleate) Size: 15 um (10 - 20 um)

• Shape: Rounded with thick cyst wall

• Contents: one to four nuclei, glycogen vacuoles, chromatoid bodies

Mode of Transmission

• Contaminated foods or drinks containing mature cysts.
• Handling food by infected food handlers.
• Flies and cockroaches that carry cysts to exposed food.
• Autoinfection (faeco-oral or hand-to-mouth infection).

Life Cycle

• Excystation in small intestine.
• Trophozoite in large intestines.
• Multiplication.
• Cyst formation (mono-nucleated, bi-nucleated, quadri-nucleated.)
• Extraintestinal spread (liver, lung, brain).

Pathogenesis and Symptomatology

• Trophozoites secrete cysteine proteinases to invade extracellular matrix, host cell lysis and necrosis forming flask-shaped ulcers.
• Amoeba spread from intestine to liver through portal circulation.
• Ulcers may be complicated by secondary bacterial infections with necrosis, sloughing, perforation, peritonitis.

Clinical Pictures

• Asymptomatic infections (cyst passers)
• Symptomatic infections:
  • Intestinal amebiasis (dysenteric or non-dysenteric colitis) -incubation period (1 week to 4 weeks)
  • Clinical picture depends on parasite virulence factors and host immune response.
  • Dysentery and diarrhea (up to 10 bowel movements).
  • In severe cases: profuse diarrhea, fever, dehydration, electrolyte imbalance.
  • Ameboma: chronic granulomatous lesion in the cecum or rectosigmoid junction.
• Extraintestinal amebiasis:
  • Liver, lung, brain abscesses.
  • Skin Involvement (amebic cutis).

Diagnosis

• Clinical and laboratory

  • Microscopic: detects trophozoites (loose stools) or cysts (formed stools)
    • Direct smear of fresh stool samples.
    • Concentration methods (increase parasite detection).
    • Permanent stained smear (trichrome or iron hematoxylin).
    • Charcot-Leyden crystals (eosinophilic protein).
    • Sigmoidoscopy: visualize ulcer or trophozoites (in aspirate or biopsy).

• Indirect: serodiagnosis (anti-amoebic antibody tests) including:

  • Immunofluorescent antibody tests (IFAT)
  • Indirect haemagglutination assays (IHAs)
  • Radioimmunoassay (RIA).
  • Enzyme-linked immunosorbent assays (ELISAs)

• Stool antigen

• Molecular diagnosis

  • Radiological investigations (ultrasound or CT) detect complications.

Treatment

• Medical treatment:
  • Metronidazole (Flagyl) or Tinidazole (Fasigyn)
  • Diloxanide furoate or Paromomycin, Luminal amoebicides (diloxanide furoate and iodoquinol).
• Surgical treatment: rupturing abscess, intestinal perforation, and appendicitis.

Prevention and Control

• Treatment of patients and carriers.
• Proper washing of vegetables.
• Sanitary sewer systems.
• Avoid using human excreta as fertilizer.
• Fly control.
• Personal hygiene measures

Balantidium coli

• Geographical distribution: worldwide, areas where pigs are raised and sanitation is inadequate.

• Habitat: large intestine (caecum, colon).

• Definitive host: Man.

• Reservoir host: Pigs, less common monkey.

• Infective stage: Mature cyst.

• Diagnostic stage: cyst and trophozoite.

• Trophozoite size: 60 × 45 µm, largest protozoon of man; Ovoid, tapers.

• Covered with cilia.

• Cytostome that extends to 1/3 of the body length.

• Macronucleus (hyaline mass), micronucleus (small, spherical).

• Granular cytoplasm, contractile vacuoles, food vacuoles (ingested microbes).

• Cyst size: 52 to 55 μm.

• Shape: Subspherical to oval.

• Two nuclei (macronucleus and micronucleus)

• Cytoplasm: granular, one or two contractile vacuoles

• Double cyst wall. row of cilia between cyst wall layers.

• Mode of transmission: similar to Entamoeba histolytica.

• Life cycle: Multiplication by transverse binary fission, forming two young trophozoites. Cysts, excystation, multiplication, trophozoites in large and small intestine, pass in feces then to environment.

• Complications: haemorrhage, secondary bacterial infection, appendicitis, intestinal perforation, and peritonitis.

• Diagnosis: history, clinical picture, laboratory tests (stool examination, direct smear, concentration methods, permanent stains). Colonoscopy/sigmoidoscopy with biopsy.

• Treatment: Tetracycline (adults 500 mg orally x 4 times daily for 10 days).

• Prevention: care in handling pigs in pig farms, slaughter houses.