Untitled Quiz

Introduction to Parasitology

• Course presenter: Chuah Candy (Ph.D.)
• Affiliation: Unit of Microbiology, Faculty of Medicine, AIMST University

Topic Outcomes

• Define terms related to parasitology
• Describe parasite classification
• Discuss transmission of medically important parasites
• Discuss life cycles of important parasites (Entamoeba, Giardia, Plasmodium, Ascaris, Ancylostoma, filarial worms)
• Apply knowledge of life cycles to laboratory diagnosis

Parasites

• An organism that acquires its needs through intimate contact with another organism (host), causing harm to the host
• Possess special structures/features: adult, developmental stages
• Classification based on:
  • Physical characteristics
  • Morphology
  • Phylogenetics
  • Location of infestation

Terminology

Ectoparasite

• Parasite residing outside the host's body
• Example: Lice on human scalp

Endoparasite

• Parasite residing inside the host's body
• Example: Ascaris lumbricoides in human intestines

Definitive host

• Host in which the parasite reaches sexual maturity, or the most important host if no reproduction occurs
• Example: Human is the definitive host for Schistosoma mansoni

Intermediate host

• Host in which the parasite undergoes development or asexual reproduction, but not sexual maturity
• Example: Snail is an intermediate host for Schistosoma mansoni, and mice/birds are intermediate hosts for T. gondii

Schistosoma spp. Life Cycle

• Diagram showing the life cycle stages, including free-swimming cercariae, snail tissue penetration, human skin penetration, circulation, migration to portal blood, development into adults, and migration to the mesenteric venules/blood vessels.
• Diagnostic and infective stages are marked in the diagram

Classification of Parasites

• Classifies parasites into Protozoa, Helminths, and Ectoparasites.
• Protozoa further divided into Intestinal, Urogenital, Blood & Tissue
• Helminths further divided based on Nematode, Cestode, Trematode
• Ectoparasites further classified with examples of Ticks, Fleas, Lice, Mites

Protozoa

General Characteristics

• Microscopic, unicellular eukaryotes
• Perform complex metabolic processes, including respiration, excretion, and digestion
• Most are free-living; some are parasitic

Morphology

• Most medically important protozoa are <50 µm
• Each cell has a nucleus (with a karyosome) and cytoplasm
• Cytoplasm divided into ectoplasm (outer, transparent layer) and endoplasm (inner, granular layer)
• Ectoplasm: Protection, locomotion, and sensation
• Endoplasm: Nutrition and reproduction

Stages

• Cyst: A resting stage that allows the parasite to survive in unfavorable conditions
• Trophozoite: The active feeding and growing stage of the parasite

Life Cycle

• Direct: One host

• Indirect: Two or more hosts

• Example diseases for direct life cycle: Ascariasis, Giardiasis, Trichuriasis

• Example diseases for indirect life cycle: Malaria, Schistosomiasis, Taeniasis

• Diagram showing direct life cycle of A. lumbricoides

• Diagram showing indirect life cycle of Plasmodium

Reproduction

• Asexual reproduction:
  • Binary fission
  • Schizogony
• Sexual reproduction:
  • Sporogony
  • Conjugation

Classification of medically important Protozoa

• Diagram showing a hierarchy of Protozoa of medical importance by Phylum

Phylum Sarcomastigophora

• Movement: Pseudopodia (Amoeba), flagella (Flagellates)
• Asexual reproduction common
• Includes: Entamoeba histolytica (intestinal amoeba), Giardia lamblia (intestinal flagellate), Leishmania (tissue flagellate), Trypanosoma (tissue flagellate)

Subphylum Sarcodina (Amoeba)

• Movement: Pseudopodia
• Includes: Entamoeba, Endolimax, Iodamoeba, Naegleria, Acanthamoeba

Entamoeba histolytica

• Third leading cause of death in developing countries due to amoebiasis
• Pathogenic amoeba associated with intestinal and extraintestional infections (liver, brain, lungs)
• Risk factors: Contaminated food/water, contaminated hands of food handlers
• Trophozoites found in large intestine: lumen, mucosa, submucosa
• Diagram showing morphology of Trophozoite form and Cyst form of E. histolytica
• Diagram showing life cycle of amoebiasis

Giardia lamblia

• Causes giardiasis, primarily in young children and is transmitted by ingestion of cysts in contaminated water/food
• Inhabits small intestine, mainly in duodenum, jejunum, upper ileum
• Has trophozoites and cysts forms
• Diagrams showing morphology of Cysts and Trophozoites of Giardia lamblia
• Diagram showing life cycle of giardiasis

Phylum Ciliophora (Ciliates)

• Movement: Cilia

• Includes: Paramecium spp., Vorticella spp., Balantidium coli (only human pathogen in this phylum)

• Balantidium coli*

• The only ciliated protozoan parasite of humans

• Found in large intestine

• Causes balantidiasis

• Morphology: Trophozoite and Cyst form

• Diagrams available for morphology

Plasmodium spp.

• Etiologic agents: P. falciparum, P. vivax, P. ovale, P. malariae, P. knowlesi
• Transmitted by female Anopheles mosquitoes
• Causes malaria, most important tropical disease
• Morphological forms: Sporozoites, Ring, Trophozoites, Schizont, merozoites, gametocytes
• Diagrams of various stages available
• Diagram showing life cycle stages, including mosquito and human stages

Helminths

• Nematoda (Roundworms):
  • Ascaris lumbricoides (most prevalent), Trichuris trichiura, Ancylostoma duodenale, Necator americanus, Strongyloides stercoralis, Enterobius vermicularis
• Classification diagrams with location/habitat and specific examples from different categories (Nematoda, Cestoda and Trematoda)
• Unique characteristics of each Class are provided, with examples

Hookworms

• Ancylostoma duodenale, Necator americanus
• Hookworms are bloodsuckers
• Infect by larvae penetrating skin from soil
• Diagram illustrating life cycle

Filarial Worms

• Caused by three species of nematodes (Wuchereria bancrofti, Brugia malayi, Brugia timori)

• Cause lymphatic filariasis, also known as elephantiasis

• Transmission through mosquitoes

• Diagram illustrating life cycle