The document provides an overview of medical protozoology, focusing on the characteristics, morphology, structure, and taxonomy of protozoa, particularly those that are parasitic to humans. It describes various life cycle stages, modes of reproduction, and ecological niches where protozoa can be found, highlighting their medical and veterinary importance. The document also categorizes protozoa into main groups, detailing their distinct characteristics and implications for human health.

1. WELCOME
TO
MEDICAL
PARASITOLOGY II

2. 1. INTRODUCTION TO
MEDICAL
PROTOZOOLOGY
2

3. Learning Objectives
Up on completion of this unit, you should be able
to:
Describe the general characteristics of
protozoans
Describe the basic structure of protozoa
Describe the basic properties of protozoa
Describe the classification of parasitic protozoa
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4. OUTLINE
 General Introduction to protozoa
 Definition
 Diversity and importance of protozoa
 General morphology of protozoa
 Basic structure of protozoa
 Basic properties of protozoa
 Protozoan life cycle stages
 Protozoan taxonomy
 General characteristics of the five main groups of
protozoa
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5. 5
What are Protozoa?

6. Definition
 single-celled eukaryotic organisms
 kingdom Protista
 Vary in size (1 -150um )
6
General introduction to protozoa

7. =Unknown until the invention of the microscope in 1675
=First recognized by antony van leewenhoek in 1676
= He described it as little animal or animacula
Int…
7

8. Diversity
 protozoa are extremely diverse organisms and
found in a variety of niches
Diversity and importance of protozoa
8

9. 9

10. Div…
 200,000 named species
 Most species are free-living in
=Freshwater
=marine environments
=decaying organic matter and soil
 Few are adapted to a parasitic life but all plant and
animal species have at least one protozoan parasite
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11. Div…
=~10,000 are parasites in a wide range of hosts
=Vertebrate
= invertebrate
= Plants
 ~20 human pathogens
 Adapted to life in a wide range of sites within the
host
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12. Ecological Niches in the Human Body
 Skin: Leishmania
 Eye: Acanthamoeba
 Mouth: Amoebae and flagellates (usually non-
pathogenic)
 Gut: Giardia, Entamoeba (and invasion to liver),
Cryptosporidium, Isospora, Balantidium
 G.U. tract: Trichomonas
 Bloodstream: Plasmodium, Trypanosoma
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13. Div…
 Spleen: Leishmania
 Liver: Leishmania, Entamoeba
 Muscle: Trypanosoma cruzi
 CNS: Trypanosoma, Naegleria, Toxoplasma,
Plasmodium
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14. Importance of protozoa
 Medical importance:
 Cause of more sickness and death than any other
disease-causing organisms
 significant damage to specific organs
 brain (African sleeping sickness), eyes
(acanthamoeba keratitis), heart (toxoplasmosis)
 reduced working capacity
 Loss of productivity
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15.  Veterinary importance:
 Death
 Potential losses
 coccidiosis costs £8 million/yr.. Prophylactics
 Animal trypanosomiasis
 Zoonoses
15
Imp…

16. General morphology of protozoa
 Protozoa exhibit a wide variety of morphologies
16

17. morp…
 Size: range from 1-150um
 The smaller members, 1-10um
 include most of the intracellular parasites (e.g.
plasmodium, Leishmania …
 The biggest in size belongs to ciliate
e.g. Balantidium coli
 Shape:
 No single shape that represent all
 Ranges from amorphous shapeless amoeba to
relatively rigid forms
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18. Basic structure of protozoa
1. Cell membrane
2. Cytoplasm: ectoplasm & endoplasm
3. Nucleus: two kinds of nuclei:
 Vesicular & compact
18

19. 1. Cell membrane: chemically similar to all eukaryotic
cells
 Thin & flexible layer called plasmalemma (sarcodina)
 Also called pellicle or ectoderm or outer membrane
 More rigid wall, usually supported by microtubules
(sub-pellicular microtubules)
 Results in more constant and uniform shape than
that of amorphous amoeba
 Characteristics of some flagellates and most
ciliates
19
Stru …

20. 20

21. 2. Cytoplasm: divided in two areas
 Ectoplasm=outer transparent layer
 Locomotion
 protection
 Sensation, respiration
 Excretion, Ingestion of food & etc
 Endoplasm= inner granular layer
 More fluid than ectoplasm, contains nuclei,
mitochondria, vacuoles & etc
 metabolism
21
Stru…

22. 3. Nucleus
 well defined nuclei bounded by nuclear envelop
 Most easily identifiable structure in protozoan cell
 Single/multiple
 Important for reproduction
 Similar in size or not
E.g. G. lamblia, ciliate (micronuclei & macronuclei)
22
Stru…

23. Stru…
 Two morphologically distinct nuclei:
 Vesicular:
 with a clearly defined internal space resulting
from irregular distribution of chromatin
 Nucleoplasm contains one or more Karyosome
 Karyosome
nucleoli-like body
 Most protozoa of humans exhibit the vesicular
type
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24. Stru…
 Compact:
 appears to be a solid mass
 densely packed chromatin
 Larger than vesicular nucleus
 Are found in ciliates
 Other structures like;
 Mitochondria: sites for aerobic metabolism
 Lysosomes: degradation of ingested materials
 Ribosome: sites for protein synthesis
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25. 25

26. A. Locomotion: Structures that mediate
26

27. B. Reproduction
-General Protozoan Reproduction
Asexual
Reproduction
Sexual
Reproduction
Binary Fission
Mutiple Fission
Endodyogeny
Conjugation
Singamy
27
Prop…

28. Prop…
1. Asexual reproduction
 Fission
 Division follows a sequence:
Organelles nucleus cytoplasm
A. Binary fission
 Each parent gives rise to two progeny
 Seen in amoeba, flagellates, ciliates
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29. Prop…
B. Multiple fission/ Schizogony/ Merogony
 Rapid organell and nuclear divisions occur at the
cell periphery
 Cytoplasmic segmentation to form separate
organisms called merozoites
 The parent or multinucleated cell is called the
schizont or segmenter and the daughter cells are
merozoites
 Seen in apicomplexan
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30. C. Endopolyogeny
 Daughter cells form in the center of the mother
cell (internal budding) rather than at the
periphery
 Endodyogeny is a form of endopolyogeny
where two daughters are formed
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Prop…

31. 31

32. 2. Sexual Reproduction
A. Conjugation
 Specialized sexual reproduction (mostly in ciliates)
 Involves nuclear exchange and union after cells join
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33. Sexual Recombination in Paramecium
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34. B. Syngamy
Union of the entire cell (gametes fuse), seen in
apicomplexan
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35. C. Feeding
 Most parasitic protozoa are heterotrophic
 ingest particulates (phagotrophy)
 Phagocytosis:
 Engulfment of solid material
 predation on bacteria or other protozoa
 Pinocytosis:
 Invagination of membrane surrounding liquids
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36.  Peristome or cytostomal feeding
 Food is ingested at a definite site, using a
specialized feeding structure
 Diffusion =absorb solutes (osmotrophy) through
cell membrane
 Food may be retained in special intracellular reserves,
or vacuoles
 Some protozoan are photosynthetic (autotrophy) or
combination
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37. D. Excretion
 Undigested particles and wastes are extruded at the
cell surface by mechanisms that are the reverse of
those used in ingestion
 diffusion (primary mechanism)
 contractile vacuole (osmo-regulation)
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38. E. Respiration
 Both aerobic (Malaria) and anaerobic respiration
(dysenteric amoeba)
 Most parasitic protozoa are facultative anaerobes
 They can live in reduced oxygen environments
38
Prop…

40. Protozoan life cycle stages/terms
1. Vegetative form: trophozoites
 stage of active feeding and reproduction
 commonly the pathogenic protozoan form
 Excystation: For the completion of life cycle, cysts
ingested by the definitive host has to change to
vegetative form
2. Resístant form: cyst
 Stage of inactivity
 Most resistant stage = hard to kill (no medication)
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41. Encystation
 Many protozoa form cysts – round cytoplasmic mass
surrounded by a rigid or semi-rigid cyst wall secreted
by organism
 Function:
 Protect against unfavorable external environmental
conditions
 Are the infective or transmissible form of parasite
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42. Conditions for encystment:
 Deficiency of host nutrient essential to the parasites
 Desiccation/dryness
 increase in osmotic pressure
 Accumulation of waste product in the medium
 Crowding
 Low pH, Temperature change
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43. 3. Oocyst:
 results from fusion of gametes in the Sporozoa
 Infective stage in most cases:
 passed in host feces in case of intestinal
protozoans or
 in gut of the mosquito vector in the case of
Plasmodium
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44. 4. Sporozoite:
 Formed within oocyst via asexual fission & infects
new host cells of
 intestinal epithelial cells in intestinal protozoans or
 hepatocytes in case of Plasmodium
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45. 5. Merozoite:
 Resulted from schizogony of sporozoites
 May infect:
 intestinal epithelial cells in intestinal coccidian or
 Red blood cells in the case of Plasmodium. …
45

46. 6. Gametocyte:
 result of merozoite cell fission
 Fusion of these results in formation of oocyst
 Other life cycle stages:
 Amastigote, Promastigote, Epimastigote ,
Trypomastigote & Metacyclic Trypomastigote
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47. Example of Protozoan life cycle
47

48. Intestinal Coccidian Life cycle
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49. 49
Life cycle of Plasmodium species

50. Protozoan Taxonomy
• Confused, controversial and constantly changing
• No universal agreement = many systems & frequent
changes
• Several bases of classification;
• light microscope = Originally based on motility
• electron microscope =Ultra-structural criteria used
since 1960’s;
 4-6 phyla? In the kingdom protista
• Molecular technique: DNA sequences
50

51. 51

52. General Characteristics of five main groups
of protozoa
1. Amoebas (Subphylum Sarcodina)
= Move by extending blunt, lobe like projections -
pseudopodia (false feet)
= Amoebas engulf food with pseudopods &
phagocytize it
52

53. Char…
53

54.  Several genera:
•Entamoeba
•Iodamoeba
•Endolimax
•Naegleria (CNS)
•Acanthamoeba (CNS)
54
Char…

55. = Move by means of rotation of a whip-like organelle
called a Flagellum (plural: flagella)
= The flagella can also be used for gathering and sorting
of food
= Some species have organelles for the purpose of food
ingestion (gullet or cytostome), and for excretion
(cytopyge)
2. Flagellates (Mastigophora)
55
Char…

56.  several genera:
 Giardia
 Chilomastix
 Dientamoeba
 Trypanosoma
 Leishmania
 Trichomonas
Char…
56

57. Giardia intestinalis
Cyst Trophozoite
57
Char…

58. Trichomonas
T. intestinalis
T. vaginalis
58
Char…

59. Trypanosoma
59
Char…

60. Leishmania
Amastigote
Promastigote
60
Char…

61. C. Apicomplexans (Phylum
Apicomplexa)
 Have specialized
organelles at tip (apex) of
cells that penetrate host
tissues
 Locomotion of mature form
by body flexion or gliding
61
Char…

62.  Obligate intracellular parasites
 usually 2 or more hosts required
 Their life cycles have asexual and sexual phases
 several forms: sporozoites, trophozoites, merozoites,
gametocytes, schizont, oocyst & cyst.
62
Char…

63. Toxoplasma gondii (Toxoplasmosis)
Bradyzoite
Gamete
Merozoite
Oocyst
Sporulated
oocyst
Sporocyst
63
Char…

64. Char…
 Includes:
1. Intestinal coccidian
 Cryptosporidium
 Isospora
 Cyclospora
2. Blood and tissue coccidian
 Plasmodium
 Toxoplasma
 Babesia
 Sarcocystis
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65. D. Ciliates (Phylum Ciliophora)
 Move and obtain food using
cilia
 Distinct cytostome (mouth)
Structure
 Dimorphic nuclei, typically
larger macronuclei and
smaller micronuclei
 Only known human pathogen
is Balantidium coli
65
Char…

66. E. Microsporans (Phylum Microsporidia)
 Obligate intracellular spore forming parasites
 Discovered in 1984 to cause chronic diarrhea and
conjunctivitis, mainly in AIDS patients
 at least 14 microsporidian species identified as human
pathogens: Enterocytozoon bieneusi, Encephalitozoon
intestinalis, Encephalitozoon hellem ….
66
Char…

67. 1.7. Protozoans associated with HIV/AIDS
 C. parvum, I. belli and C. cayatenensis: causing
enteritis
 Microsporidia species: causing a diarrhea with
wasting, eye disease, and disseminated disease
 Pneumocystis carnii: causing life threatening
pneumonia
 Blastocystis hominis: cause severe enteritis
67

68. Pro …
T. gondii: causing cerebral toxoplasmosis
Leishmania species: emerging as a major
pathogens in HIV infected persons
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