Protozoan and Amoeba

• Protozoa


  Unicellular organisms and the lowest form of animal life
• Protozoa


  • Cells contain a nucleus and membrane-bound organelles
  • Can move independently
• General characteristics of protozoa

  • Often require a wet environment for feeding, locomotion, osmoregulation, and reproduction
  • Categorized into cysts - infective stage/resting stage (tough cell wall)
  • Trophozoites - vegetative (feeding/growing)
  • Can be transmitted through biological vectors
• General structures of protozoa

  • Nucleus
  • Cytoplasm - ectoplasm (outer part, locomotion, food) and endoplasm (inner granular part, nucleus and organelles, vacuoles)
  • Locomotory apparatus - cilia, flagella, pseudopodia
  • Apical complex - penetration of target cells
• Reproduction in protozoa


  • Sexual - Conjugation, Gametogony or syngamy
  • Asexual - Binary fission, Multiple fission/schizogony, Endodyogeny
• Conjugation


  Two organisms join together and reciprocally exchange nuclear material, occurs in ciliates
• Gametogony or syngamy


  Occur in sporozoa, production of male and female gametocytes → zygote → sporozoite
• Binary fission


  A single parasite divides into two or more equal number of parasites, occurs in amoebae, flagellates, ciliates
• Multiple fission/schizogony


  Nucleus undergoes several divisions to produce merozoites, exhibited by Plasmodium spp.
• Endodyogeny


  Multiply by internal budding resulting into the formation of two daughter cells, exhibited by Toxoplasma spp.
• Classification of protozoa


  • Ciliophora
  • Sarcomastigophora - Sarcodina, Mastigophora
  • Apicomplexa
  • Microspora
• Sarcodina


  • Appears fleshy, have no permanent locomotory organ → pseudopodia, includes amoebae
• Mastigophora


  • Appears like a whip or flagellum, possess whip-like flagella, includes flagellates
• Apicomplexa


  • Formerly known as sporozoa, possess an apical complex, have an alternating sexual and asexual life cycle
• Ciliophora


  • Move using cilia
• Microspora


  • Made up of minute intracellular parasites, frequently cause disease in immunodeficient subjects
• Organs of locomotion in protozoa

  • Sarcodina - pseudopodia
  • Mastigophora - flagella
  • Ciliophora - cilia
• Penetrating organs in protozoa

  • Apicomplexa - apical complex at anterior end
  • Microspora - highly coiled polar filament
• Only protozoan parasite found in lumen of human small intestine: Giardia lamblia
• Largest protozoa: Balantidium coli
• Most common protozoan parasite: Toxoplasma gondii
• All free-living amoebae are opportunistic pathogens
• Important protozoan parasites and their diseases

  • Entamoeba histolytica - Amoebic dysentery, amoebic liver abscess (ALA)
  • Naegleria fowleri - Primary amoebic meningoencephalitis (PAM)
  • Acanthamoeba - Granulomatous amoebic encephalitis (GAE), amoebic keratitis
  • Giardia lamblia - Malabsorption, diarrhoea
  • Trichomonas vaginalis - Vaginitis, urethritis
  • Trypanosoma brucei - Sleeping sickness
  • Trypanosoma cruzi - Chagas' disease
  • Leishmania donovani - Kala azar, Post-kala azar dermal leishmaniasis
  • Leishmania tropica - Cutaneous leishmaniasis (oriental sore)
  • Leishmania braziliensis - Mucocutaneous leishmaniasis
  • Toxoplasma gondii - Toxoplasmosis
  • Microsporidia - Diarrhoea
  • Plasmodium - Malaria
  • Babesia - Babesiosis
  • Cystoisospora belli - Diarrhoea
  • Cryptosporidium parvum - Diarrhoea
  • Balantidium coli - Dysentery
• Amoeba


  • Can assume any shape, move with the use of pseudopodia (false feet), groups of medical importance - intestinal, free-living
• All amoeba are commensals except E. histolytica, inhabit the colon except E. gingivalis, have a cystic stage except E. gingivalis
• Morphologic stages of amoeba

  • Trophozoite - motile, feeding stage/vegetative stage, diarrheic/liquid stool, destroyed by iodine
  • Cyst - non-motile, non-feeding stage/infective stage, well-formed stool, capable of resisting heat or acidic environment
• Intestinal amoeba


  • E. histolytica
  • E. dispar
  • E. moshkovskii
  • E. hartmanni
  • E. coli
  • E. nana
  • E. polecki
  • Iodamoeba butschlii
• Nuclear characteristics of trophozoites are identical to their corresponding cysts
• Trophozoites are characteristically delicate and fragile; have the ability to use and produce pseudopods
• Life cycles of all intestinal amebas are similar
• Most common mode of transmission is through ingestion of infective cysts in contaminated food or water
• Cysts may be studied in fresh condition by staining with D'ANTONI's iodine stain
• Satisfactory stain for amoeba is IRON and HEMATOXYLIN
• Excystation


  Morphologic conversion from the cyst from into the trophozoite form, occurs in the ileocecal area of the intestine, replication only occurs in the trophozoite stage
• Encystation


  Conversion of trophozoites to cysts, occurs in the intestine when the environment becomes unacceptable for trophozoite multiplication
• Intestinal amoeba


  • Pathogenic - E. histolytica
  • Commensals - E. dispar, E. moshkovskii, E. hartmanni, E. coli, E. polecki, E. nana, I. butschlii, E. gingivalis
• Free-living amoeba


  • Acanthamoeba spp.
  • Naegleria fowleri
• Intestinal amoeba are characterized by a vesicular nucleus, centrally located small karyosome, varying numbers of chromatin granules adhering to the nuclear membrane
• E. histolytica, E. dispar, and E. moshkovskii are morphologically identical, differentiated through isoenzyme analysis, polymerase chain reaction restriction fragment length polymorphism (RFLP), typing with monoclonal antibodies
• Entamoeba histolytica


  • Has a worldwide prevalence, especially where sanitation is poor, most common in tropical developing countries, majority of cases are asymptomatic, inhabit the human colon, completes its life cycle in the human host, most invasive of the Entamoeba parasites, associated with: intestinal amebiasis, amebic colitis, amebic dysentery, and extraintestinal amebiasis