protozoa

• Symbiosis

  Relationship between different organisms
• Types of symbiosis

  • Commensalism - No benefit nor harm (host)
  • Mutualism - Mutual benefit
  • Parasitism - Harm on host
• Classification of parasites based on habitat

  • Ectoparasites - Outside, infestation
  • Endoparasites - Inside, infection
• Classification of parasites based on dependency

  • Obligate - Needs host to complete life cycle
  • Facultative - Can live without a host
• Classification of parasites based on mode of living

  • Permanent - Remain inside from early life to maturity
  • Intermittent - Invades during feeding time
  • Incidental - Unusual host
  • Transitory - Uses host only for development
  • Erratic - Unusual invasion site
• Types of hosts

  • Definitive - Harbors the adult/sexual stage
  • Intermediate - Harbors larval/asexual stage
  • Reservoir - Harbors parasite as carrier, may act as additional source of infection
  • Paratenic - Means of transport
• Source of exposure

  Most common is soil
• Mode of transmission

  Most common is fecal-oral route
• Portal of exit


  Most common is anus
• Pathogenicity

  Dynamics of disease process
• Classification of parasites

  • Protozoa - Single celled
  • Metazoa (helminths) - Multi celled
• Classification of protozoa based on motility

  • Amoeba - Pseudopods (crawling)
  • Flagellates - Flagella (crawling)
  • Sporozoa - No motility organ (gliding)
  • Ciliates - Cilia
• Classification of helminths based on shape and structure

  • Nematodes (roundworms)
  • Platyhelminthes

  1. Trematodes (Flukes)
  2. Cestodes (Tapeworms)
• Entamoeba histolytica

  Classic flask shaped ulcer on cecum & colon
• Infective stage (IS)

  Cyst
• Pathogenic stage (PS)

  Trophozoite
• Mode of transmission (MOT)

  Fecal-oral (contaminated water/food), sexual transmission
• Pathogenesis of Entamoeba histolytica

  • Amoebic dysentery - Bloody mucoid stool
  • Amoeboma - Mass inside cecum
  • Extraintestinal - Amoebic liver abscess, Amoebic pneumonitis
• Diagnosis of Entamoeba histolytica

  Direct fecal smear - Loose watery (trophozoite), Formed (cyst)
• Treatment of Entamoeba histolytica

  Drug of choice - Metronidazole, Alternative - Tinidazole
• Giardia lamblia

  Trophozoite has an "old man facies" with sucking disc, Falling leaf motility
• Pathogenesis of Giardia lamblia

  Giardiasis (Traveler's diarrhea)
• Diagnosis of Giardia lamblia

  Direct fecal smear - Cyst & trophozoite, String test - Alternative
• Treatment of Giardia lamblia

  Metronidazole, Tinidazole, Nitazoxanide
• Trichomonas vaginalis


  Only protozoa with no cyst stage
• Infective stage (IS)

  Trophozoite
• Mode of transmission (MOT)

  Sexual transmission, Vertical transmission
• Pathogenesis of Trichomonas vaginalis

  Trichomoniasis - Vaginal mucosa in women, Prostate & urethra in men, Strawberry cervix with watery to foul greenish yellow discharge
• Diagnosis of Trichomonas vaginalis

  Wet mount (Vaginal, urethral, prostatic discharge and/or urine sample)
• Treatment of Trichomonas vaginalis

  Metronidazole
• Balantidium coli

  Largest protozoa, Cytostome - Primitive mouth & with boring motility
• Reservoir

  Pig/monkey
• Mode of transmission (MOT)

  Fecal-oral (contaminated water/food)
• Pathogenesis of Balantidium coli

  Balantidiasis - Same manifestation with E. histolytica but without extraintestinal invasion
• Diagnosis of Balantidium coli

  Direct fecal smear
• Treatment of Balantidium coli

  Drug of choice - Oxytetracycline & Iodoquinol
• Acanthamoeba castellani

  Can invade through contact lenses
• Mode of transmission (MOT)

  Aspiration/direct invasion of eye (soil/cold water)
• Pathogenesis of Acanthamoeba castellani

  Granulomatous Amoebic Encephalitis - Immunocompromised host with brain abscess, Keratitis - Eye infection through direct contact
• Diagnosis of Acanthamoeba castellani

  CSF smear, Brain tissue, Corneal scrapings stained with Calcoflour white