Parasitology

• Parasitology


  The study of the interaction between parasites and their hosts
• Parasitism


  The study of important parasites which causes diseases to humans (classification, symptoms, disease, lifecycle, transmission, treatment)
• Clinical parasitology


  The study of important parasites which causes diseases to humans (classification, symptoms, disease, lifecycle, transmission, treatment)
• Taxonomic classification/rank rules

  • Scientific names are always italicized
  • The genus is always capitalized
  • The species is never capitalized, even when it refers to the name of a place or person
  • In its first use within a particular document, the genus is always written in full. In subsequent uses, the genus can be abbreviated using the first initial and a period
  • A species name is never used without a genus or genus abbreviation
  • If you must use a common name, first define it in terms of the scientific name
• Major divisions of parasites

  • Ectoparasite
  • Protozoa (Phylum)
  • Helminths
• Ectoparasites


  • Insecta
  • Arachnida
• Insecta ectoparasites


  • Pediculus humanus (head louse, body louse)
  • Pthirius pubis (crab louse)
  • Pulex irritans (human flea)
• Arachnida ectoparasites


  • Sarcoptes scabiei (itch mite)
  • Demodex folliculorum
  • Demodex brevis
• Protozoa (Phylum)


  • Ciliata
  • Sarcodina
  • Mastigophora
  • Sporozoa
  • Apicomplexan
  • Coccidians
• Helminths


  • Nematoda
  • Trematodes
  • Cestodes
• Relationships of the medically important parasites

  • Kingdom Protista
  • Protozoa
  • Sarcodina
  • Sporozoa
  • Mastigophora
  • Digenia
  • Nematoda
  • Cestoda
  • Insecta and Arachnida
• Medical parasitology


  The science that deals with organisms living in the human body (the host) and the medical significance of this host-parasite relationship
• Protozoa

  Provided with nucleus/nuclei, cytoplasm, outer limiting membrane, and cellular elaborations called organelles
• Protozoa

  • Locomotory apparatus: cilia, flagella and pseudopodia
  • Require a wet environment for feeding, locomotion, osmoregulation, and reproduction
• Protozoan parasite phyla

  • Sarcomastigophora
  • Ciliophora
  • Apicomplexa
  • Microspora
• Apicomplexa


  They have a unique organelle called an apicoplast, which is a non-photosynthetic plastid that helps them penetrate host cells. They also have an apical complex structure that contains several rings, including a conoid in some species. They are spore-producing and lack contractile vacuoles and locomotor processes.
• Microsporidia


  A group of spore-forming unicellular parasites. These spores contain an extrusion apparatus that has a coiled polar tube ending in an anchoring disc at the apical part of the spore. They were once considered protozoans or protists, but are now known to be fungi, or a sister group to fungi.
• Sarcomastigophora protozoan parasites

  • Sarcodina: Entamoeba histolytica, Entamoeba coli, Entamoeba dispar, Entamoeba hartmani, Entamoeba polecki, Entamoeba gingivalis, Iodamoeba butschlii, Endolimax nana, Naegleria fowleri, Acanthamoeba spp.
  • Mastigophora: Chilomastix mesnili, Dientamoeba fragilis, Giardia Lamblia, Pentatrichomonas Hominis, Trichomonas tenadx, Trichomonas vaginalis, Leishamania braeilienis, Leishamania donovani, Leishamania tropica, Trypanosoma brucei complex, Trypanosama cruzi
• Ciliophora protozoan parasite

  • Balantidium coli
• Apicomplexa protozoan parasites

  • Babesia spp., Cryptosporidium hominis, Cysclosporia cayatanensis, Isospora belli, Plasmodium spp., Toxoplasma gondii
• Microsporidia protozoan parasites

  • Enterocytozon bineusi, Encephalitozon spp., Vittaforma cornea, Trachipleistophora homimis, Pleistophora spp., Branchiola vesicularum, Microsporidium spp.
• Intestinal amoebae


  • Entamoeba histolytica, Entamoeba dispar, Entamoeba hartmanni, Entamoeba coli, Entamoeba polecki, Endolimax nana, Iodamoeba butschlii
• Intestinal amoebae life cycle

  1. Cysts ingested and excyst in small intestine

  2. Trophozoites proliferate by binary fission in colon

  3. Both cysts and trophozoites passed in feces, but only mature cysts are infective
• Entamoeba histolytica

  Only amebic species capable of invading tissues and causing disease
• Entamoeba histolytica

  • Pseudopod-forming nonflagellated parasite
  • Most invasive of the parasites in the Entamoeba family
  • The only member of the family to cause colitis and liver abscess
• Stages in Entamoeba histolytica life cycle

  • Cyst (infective)
  • Trophozoite (invasive)
• Entamoeba histolytica cyst

  Quadrinucleate, resistant to gastric acidity and desiccation, can survive in moist environment for weeks
• Entamoeba histolytica transmission

  1. Fecal-oral contact

  2. Direct colonic inoculation through contaminated enema equipment
• Entamoeba histolytica life cycle

  1. Ingestion of mature cysts

  2. Excystation in small intestine, trophozoites migrate to large intestine
• Clinical diseases caused by Entamoeba histolytica

  • Amebic dysentery
  • Amebic colitis
  • Liver abscess
• Amebic dysentery

  Acute disease characterized by bloody diarrhea with abdominal cramping, invasion of intestinal mucosa leading to ulceration, perforation and peritonitis
• Amebic colitis


  Mimic ulcerative colitis, less severe than amebic dysentery (may include non-bloody diarrhea, constipation, abdominal cramping, weight loss), develops small, pinpoint mucosal ulcerations that expand within submucosa to form flask-shaped ulcers
• Amebic liver abscess


  Most common form of extraintestinal amebiasis (5% of patients with history of intestinal amebiasis), symptoms include fever and right upper quadrant pain
• Entamoeba histolytica invasiveness

  • Gal/Gal Nac lectin mediates adherence to host cells
  • Amebapores form pores in host cell membranes
  • Cysteine proteinases are cytopathic for host tissues
• Immunity to Entamoeba histolytica

  Natural immunity (mucin inhibition of amebic attachment to mucosal cells)<|>Systemic circulation (complement-mediated killing of trophozoites)<|>Activated T-cells kill E.histo by direct lysis, cytokine production, and providing helper effect for B cell Ab
• Immunosuppression during acute Entamoeba histolytica infection

  T cell hyperresponsiveness<|>Suppressed proliferation and cytokine production<|>Depressed delayed type hypersensitivity<|>Macrophage suppression
• Entamoeba histolytica diagnosis methods

  • Microscopic examination of minimum 3 stool specimens
  • Fresh stool examination within 30 mins (trophozoite identification)
  • Saline and methylene blue staining
  • Saline and iodine staining
  • Formalin ether concentration test (FECT)
  • Merthiolate iodine formalin concentration test (MIFC)
• Morphological structures observed in diagnosis

  Size of cyst<|>Number of nuclei<|>Location and appearance of karyosome<|>Appearance of chromatoid bodies<|>Presence of cytoplasmic structures like glycogen vacuole
• Laboratories relying on morphology must report as "E. histolytica/E. dispar" if not using immunologic or molecular methods to differentiate
• Serological tests for Entamoeba histolytica

  • Indirect hemagglutination (IHAT)
  • Counter immunoelectrophoresis (CIE)
  • Agar gel diffusion (AGD)
  • Indirect fluorescent antibody test (IFAT)
  • Enzyme-linked immunosorbent assay (ELISA)