Protozoan Parasites Quiz

Parasitology 2025

• Parasitology is the study of parasites, their hosts, and the relationship between them.
• Key reference used for this course is "Foundations of Parasitology" by Gerald D. Schmidt & Larry S. Roberts (8th ed.)
• Key Objectives include: Classifications of human and animal parasites, Morphology and life cycles, and Parasite infections to humans.
• Course content will include:
  • Introduction and definitions of key terms
  • Classification
  • Protozoans: General characteristics & Morphology, Various classifications, Specific examples of public health importance, and resulting diseases
  • Helminths: General characteristics & Morphology, Various classifications, Specific examples of public health importance, and resulting diseases
• Learning outcomes include: Describing two main groups of human parasites, and stating their characteristics and morphologies, explaining life cycles of specific parasites of public health importance, and knowing/predicting how these parasites' transmission can be prevented.

Key Terms

• Parasite: An organism that receives nourishment and shelter from another organism (host) and is entirely dependent on it for all or part of its life cycle and metabolic requirements. Parasites may or may not cause a disease.
• Host: The organism that harbors the parasite.
• Vector: A living carrier that transports a pathogenic organism from an infected host to a non-infected host (e.g., female Anopheles mosquito, Tsetse fly).
• Temporary parasite: Visits a host briefly for a short period
• Permanent parasite: Stays with host for its entire life
• Facultative parasite: Lives a parasitic life when an opportunity arises, but can also live free-living.
• Obligatory parasite: Cannot exist without its parasitic way of life. Lives only as a parasite.
• Accidental/occasional parasite: Attacks an unusual host, i.e., not its normal host.
• Ectoparasite: Lives on the outside of the host, i.e., on the surface body of host
• Endoparasite: Lives inside the host e.g., blood, tissues, body cavities of host.

Macroscopic Parasites

• Large enough to be seen with the naked eye.
• Example: Worms and arthropods.
• Typically do not multiply within the host.
• Infection levels depend on the initial numbers of organisms entering the host body.
• One infectious stage matures into one reproductive stage.
• They often occur in aggregated or clumped populations
• They have important clinical implications

Microscopic Parasites

• Viruses, bacteria, protozoa, and fungi.
• Some grow intracellularly.
• Replicate within the host, causing large numbers of progeny and overwhelming infection.
• Often difficult to treat due to non-selective action of some antibiotics.

Intracellular parasites

• Live inside cells (e.g., HIV within lymphocytes).
• Protected from many host defense mechanisms.
• Difficult to treat due to the non-selective nature of some antibiotics.
• Examples include Plasmodium (malaria), some viruses.

Extracellular parasites

• Do not invade cells. Instead, they proliferate in the extracellular environment, often enriched with body fluids.
• Example: Trypanosoma spp.
• Some bacteria don't penetrate cells but adhere, causing disease by secreting toxins.

Classification of Parasites

• Protozoa: Microscopic, single-celled eukaryotic organisms (e.g., Plasmodium, Entamoeba, Giardia)
• Helminths: Macroscopic, multicellular worms (e.g., tapeworms, flukes, roundworms)

Protozoa

• Classified into six phyla based on microscopic morphology.
• Most human-pathogenic protozoa belong to Sacromastigophora and Apicomplexa.
• Transmission common through ingestion of contaminated water/food or via insect vectors.
• Unicellular
• Possess organelles for locomotion.
• Can be intracellular or extracellular.

Sarcodina

• Include genus Amoeba.
• Cells are shaped irregularly, with soft, transparent, flexible pellicles.
• Some have external shells or skeletons, with cytoplasm divided into ectoplasm (outer) and endoplasm.
• Obtain energy by consuming food particles and organic matter.
• Reproduction by syngamy or by division/budding. (e.g., Entamoeba, Endolimax, Iodamoeba, Naegleria, Acanthamoeba).
• Cause amoebiasis

Flagellates (Mastigophora)

• Typically have one or more whip-like flagella.
• Includes intestinal and genitourinary flagellates (e.g., Giardia, Trichomonas).
• Blood and tissue flagellates (e.g., Trypanosoma, Leishmania).
• Cause diseases like Trypanosomiasis (sleeping sickness, Chagas disease) and Trichomoniasis

Apicomplexa

• Primarily intracellular parasites
• Possess an apicoplast and an apical complex.
• Undergo complex life cycles with alternating sexual and asexual stages in multiple host
• Examples of Apicomplexa: Isospora, Toxoplasma, Plasmodium

Ciliophora

• Complex protozoa bearing cilia for locomotion.
• Contain two types of nuclei and a contractile vacuole.
• Example: Balantidium coli (intestinal ciliate of humans and pigs.

Trematodes (Flukes)

• Commonly known as flukes
• Leaf-like, unsegmented organisms.
• Hermaphroditic, except Schistosomes which are dioecious
• Lack hooks and suckers
• Have alimentary canal (incomplete)
• Example: Schistosoma (causes schistosomiasis).

Helminths

• General characteristics, life cycles, and different classes of helminths (roundworms, flatworms(including cestodes and trematodes)

Nematodes (Roundworms)

• Elongated, cylindrical, unsegmented bodies
• Separate sexes (dioecious).
• Lack hooks and suckers.
• Complete alimentary canal and body cavity
• Example: Ascaris lumbricoides, Enterobius vermicularis, Trichuris trichiura, Ancylostoma duodenale, Necator americanus, Strongyloides stercoralis.
• Cause various intestinal and somatic infections

Filarial worms

• Parasitic worms belong to Filarioidea type.
• Spread by blood-feeding black flies or mosquitoes
• Divided into three groups based on their body location (lymphatic, subcutaneous, serous cavity).
• Examples: Wuchereria bancrofti, Brugia malayi, Brugia timori, Onchocerca volvulus, Loa loa, Mansonella perstans, Mansonella ozzardi.
• May cause elephantiasis.

Arthropods

• Invertebrates with exoskeletons, segmented bodies, and jointed appendages.
• Many are vectors for parasitic diseases.
• Important examples: Mosquitoes (Anopheles, Aedes), Fleas, Body lice

Parasite Infections

• Summary of each disease, its symptoms and transmission