Protozoology Lecture 1 - Parasitic Protozoa

Course Information

• Course: Hematology and Parasitology (BCh 507)
• Part: Protozoology
• Lecture: 1
• Prepared by: Dr. Samir El-Abbassy

Parasitic Protozoa

• Single-celled organisms performing all vital functions (nutrition, reproduction, respiration, excretion, etc.)
• Composed of a mass of protoplasm: plasma membrane, cytoplasm, and nucleus.
• Cytoplasm differentiated into an outer layer (ectoplasm) and an inner layer (endoplasm).
• Plasma membrane and ectoplasm function in protection, respiration, excretion, locomotion, and ingestion.
• Endoplasm contains nucleus, contractile (excretory) vacuoles, and food vacuoles.
• Nucleus composed of endosome (karyosome), nuclear envelope, chromatin patches, and nuclear fluid.
• Locomotion through pseudopods, cilia, and flagella.
• Respiration is either aerobic or anaerobic.
• Excretion and osmoregulation by diffusion or contractile vacuoles.
• Nutrition accomplished by absorption through the plasma membrane, engulfing solid food by pseudopods (amoeba), or ingestion through a cytostome (ciliates and flagellates), or by diffusion.

Reproduction

• Asexual reproduction: binary fission, multiple fission (schizogony), and budding.
• Sexual reproduction: Syngamy (complete fusion of two gametes) and conjugation (temporary union of two individuals of the same species).

Encystment

• Trophozoite secretes a cyst to survive outside the host.

Phylum Sarcomastigophora

• Entamoeba histolytica: large intestine of humans (pseudopods).
• Entamoeba coli: large intestine of humans (pseudopods).
• Giardia lamblia: small intestine (flagellates).
• Trichomonas vaginalis: urogenital tract (flagellates).

Phylum Ciliophora (Cilia)

• Balantidium coli: large intestine of humans.

Phylum Apicomplexa

• Does not possess means of locomotion.
• Cryptosporidium: small intestine.
• Toxoplasma gondii: brain, muscles, eyes, and lymph nodes.

Cyst vs. Trophozoite

• Cyst: infective stage, inert, resists gastric acidity and environmental conditions, formed samples.
• Trophozoite: pathogenic stage, feeds, divides, causes pathology, dies within ½ hour outside the host, liquid samples.

E. histolytica Morphology

• Trophozoite: 12-30 µm, moves with pseudopods, differentiated into ectoplasm and endoplasm, single nucleus with a clear membrane, central endosome, chromatin patches, cytoplasm with food vacuoles containing red blood cells.
• Cyst: 10-20 µm, mature cyst contains four nuclei, immature cyst contains one or two nuclei, endosome is small and centrally located; cytoplasm contains chromatoid bodies and glycogen vacuoles.

E. coli Morphology

• Trophozoite: 20-40 µm, many pseudopods, no differentiation of cytoplasm into ectoplasm and endoplasm, single nucleus with a peripheral endosome, food vacuoles may contain bacteria and undigested food.
• Cyst: 20-30 µm, 8 nuclei, represents the infective stage.

Differences between E. histolytica and E. coli

• E. histolytica is pathogenic, while E. coli is non-pathogenic.
• E. histolytica trophozoites are smaller (10-30 µm), with a centrally located nucleus and karyosome. E. coli trophozoites are larger (20-40 µm), and have a peripherally located nucleus.
• E. histolytica cysts contain 4 nuclei, and E. coli cysts contain 8 nuclei.

Giardia lamblia

• Cosmopolitan distribution, human host, small intestine habitat, Two forms trophozoite and Cyst, transmission by consuming contaminated water or food with mature cysts.

Giardia lamblia Morphology

• Trophozoite (10-20 µm): pear-shaped, bilaterally symmetrical, 2 nuclei, 2 median bodies, 4 pairs of flagella (1 anterior, 1 posterior, 1 ventral, 1 caudal).
• Cyst (10-12 µm): 4 nuclei, 4 median bodies, 2 ventral grooves.

Giardia lamblia Life Cycle

• Trophozoites reproduce by simple binary fission.
• Trophozoites transform into cysts (infective stage).
• Cysts are passed out with the feces.
• Water and food become contaminated by the cysts.
• Infection occurs by eating food or drinking water contaminated with mature cysts.

Giardia lamblia Pathogenicity and clinical picture

• Giardiasis causes acute diarrhea, inflammation in the duodenal wall, abdominal cramps, abdominal distension, vomiting, loss of weight, biliary duct trophozoites attack the liver leading to jaundice and biliary colic in the acute stage.

Giardia lamblia Laboratory diagnosis

• Direct stool examination to detect trophozoites and cysts
• Examination of duodenal aspirate for trophozoites
• Detection of coproantigen of Giardia using an immunoassay

Trichomonas vaginalis

• Cosmopolitan distribution, human definitive host, no intermediate host, inhabiting urethra, urinary bladder, prostate gland and seminal vesicle in males, vagina, urethra, cervix, uterus and urinary bladder in females, morphology - trophozoite only (17-20 µm), pear-shaped, 5 flagella (4 anterior, 1 posterior), undulating membrane, axostyle, nucleus, parabasal fibril, parabasal body, costa, sexual intercourse transmission,

Trichomonas vaginalis Pathogenesis and clinical picture

• Transmission through sexual intercourse or indirect contact via contaminated articles.
• Causes vaginitis (burning sensation, itching, creamy discharge) and inflammation in the genital organs of both males and females.

Trichomonas vaginalis Laboratory diagnosis

• Microscopic examination of fresh vaginal discharge, semen, and urine.
• Culture of discharge
• Immunological tests (direct fluorescent antibody test, enzyme immunoassay)
• Molecular techniques

Dive into the fascinating world of parasitic protozoa in this first lecture of the Hematology and Parasitology course. Explore the structure, functions, and locomotion of these single-celled organisms, along with their unique methods of respiration, nutrition, and excretion. This quiz will test your understanding of the vital functions that these organisms perform.