Parasitic Protozoa: An Introduction

Introduction to Parasitic Protozoa - Outline

• This lecture covers an introduction to parasitic protozoa, including their definition, basic properties, transmission, and life cycle.
• It reviews major groups of parasitic protozoans, including Flagellates (Mastigophorans), Amoebae (Sarcodinians), Apicomplexan (Sporozoans), and Ciliates (Ciliophorans).
• Discussion of diagnosis and treatment of protozoan parasitic infections, and future research directions in the subject.

Learning Outcomes

• Classify protozoans.
• Describe the morphology of each major group of protozoa.
• Explain the pathophysiology, life cycle, infective stages, modes of transmission, epidemiology, prevention, and control of protozoan parasites.
• Describe diagnostic features of each parasite.
• List the different specimens used for appropriate diagnostic procedures for each parasitic infection.

Major Groups of Parasitic Protozoans

• Protozoa is divided into Sarcodina, Flagellata, Sporozoa, and Infusoria.
• Sarcodina includes Amoeba.
• Flagellata (or Mastigophora) includes Leishmania, Trypanosoma, Giardia, and Trichomonas.
• Sporozoa (or Apicomplexa) includes Plasmodium, Sarcocystis, Cryptosporidium, Toxoplasma, Babesia, and Isospora.
• Infusoria (or Ciliophora) includes Balantidium.

Parasitic Amoebae - Phylum Sarcodina

• Phylum Sarcodina includes Class Rhizopodea, Subclass Amoebida, Family Entamoebidae, Genus Entamoeba, Genus Iodomoeba, and Genus Endolimax.
• These amoebae move via pseudopodia, exhibiting amoeboid movement, and lack a definite cell shape.
• They are holozoic or saprozoic, asexual, and live in aquatic environments.
• They have sensory and contractile organelles and can form cysts.
• Amoebas in Phylum Sarcodina can form temporary cytoplasmic extensions called pseudopodia for locomotion and feeding.
• Pseudopodia are flexible and can extend or retract to change the shape and direction of movement.
• Sarcodina lack a rigid cell wall, distinguishing them from other protozoa groups, and have a flexible cell membrane.
• Sarcodina feed by engulfing prey through pseudopodia, capturing bacteria, algae, other protozoa, and organic particles.
• They can ingest and digest solid food particles (holozoic) or feed on dissolved organic matter (saprozoic).
• Reproduction occurs asexually via binary fission, where the parent cell divides into two identical daughter cells, and sexually via gamete fusion.
• Habitats include freshwater, marine environments, and damp terrestrial environments; capable of parasitic or symbiotic lifestyles.
• Diversity includes both free-living and parasitic species
• Amoeba proteus, Entamoeba histolytica, and Naegleria fowleri are examples.
• Contractile vacuoles regulate water balance, and eyespots (stigma) detect light.
• In adverse conditions, some sarcodines form dormant, protective cysts for survival and dispersal.

Entamoeba histolytica

• Morphology includes irregular trophs (15-20 µm, 1 nucleus) and cysts (12-15 µm, 4 nuclei when mature).
• Habitat: Large intestine of primates.
• Pathogenesis: Causes amoebic colitis/dysentery, liver abscess, and lung abscess.
• Symptoms: Can range from mild diarrhea to severe dysentery with bloody stool, abdominal pain, cramping, weight loss, and fatigue; can also cause organ-specific symptoms.

Entamoeba histolytica - Life Cycle and Transmission

• The life cycle involves an infective cyst (dormant form) and a motile trophozoite (active, feeding, and multiplying form).
• It spreads through ingestion of fecal material, or consumption of contaminated food/water.

Entamoeba histolytica - Diagnosis and Treatment

• Diagnosis includes stool examination with microscopy, serological tests, molecular techniques (PCR), proctosigmoidoscopy, liver biopsy, computed tomography, and magnetic resonance imaging.
• Treatment options include metronidazole, tinidazole, and nitazoxanide.
• Cyst eradication options include iodoquinol, paromomycin, and diloxanide furoate.
• In some cases, drainage of abscesses via computed tomography (CT)-guided aspiration. Surgical intervention may also be necessary.

Other Parasitic Amoebae

• Includes Entamoeba dispar, Entamoeba polecki, Entamoeba hartmanni, Entamoeba coli, Iodomoeba bütschlii, and Endolimax nana.

Nonpathogenic Amoebae

• Non-pathogenic amoeba inhabit the large intestine of primates and exist as cysts and trophozoites.
• Transmission happens via ingestion of contaminated food, water, or fecal material.
• They are non-pathogenic (commensal).
• These can be mistaken for pathogenic amoeba.
• Diagnosed via microscopic stool exam, serological tests, or molecular tests.
• Treatment/prevention involves sanitation.

Entamoeba gingivalis

• Entamoeba gingivalis is a nonpathogenic amoeba found in some people
• Morphology: Spherical to oval shape, 10-30 µm in diameter, single nucleus, often with ingested bacteria.
• Habitat: Oral cavity, especially with poor oral hygiene and dental plaque.
• Pathogenesis: Mostly non-pathogenic but may be associated with localized oral infections.
• Diagnosis: Microscopic exam of dental plaque.
• Treatment: Oral hygiene.

Entamoeba gingivalis - Morphology, Habitat and Treatment

• Has an amoeboid protozoan with a spherical to oval shape ranging from 10 to 30 micrometers, and a single nucleus and often ingested bacteria within its cytoplasm.
• Habitat-resides in the oral cavity, particularly in the gingival crevices, dental plaque, and periodontal pockets, associated with dental plaque.
• Non-pathogenic, therefore specific treatment is not required, but maintaining good oral hygiene practices and regular dental cleanings can prevent overgrowth.