Characters of protozoa

1. Introduction to Protozoa

2. General Account
• Unicellular animal with full functions
• Distribute widely: water,soil, etc.
• Total species 65,000
– Free-living: majority
– Parasitic: about 10,000

3. Medical Protozoa
• Pathogenic protozoa
• Opportunistic parasite
• Not normally pathogens
– Become pathogenic due to impairment of host
resistance
– Clinical importance of the AIDS epidemic

4. Basic Structures
• Plasma membrane: Cytoplasm
– Ectoplasm: locomotion , ingestion, etc
– Endoplasm: metabolism
• Nuclear
– Vesicular form or compact form
• Locomotive organelle
– Pseudopodium, flagellum, cilia

5. Mode of Reproduction
• Asexual reproduction
– Binary fission: results in 2 daughter cells
– Schizogony: multiple fission, results in multiple cells
– Endodyogony: by internal budding
results in 2 cells
• Sexual reproduction
– Conjugation: exchange of nuclear
materials of 2
– Gametogony: sexually differentiated cells unit  zygote

6. Life Cycle Patterns
• One stage form
– Trophozoite ( take food, be mobile, multiply)
• Two-stage form
– Trophozoite & cyst (not mobile, with cyst wall)
• Two-host form
– Mammals – mammals
– Mammals - insect vectors

7. Characteristics of
Protozoan in Infection
• Proliferation-parasitemia
• No larva and adult differentiation but stage
differences
• May be intracellular lodgment
• Opportunistic & accidental infections (free-
living)

8. Medical Important Species
• Amebae
• Flagellates
• Sporozoites
• Ciliates

9. Pathogenic Intestinal Amoeba
Entamoeba histolytica

10. Morphology
• Trophozoite
– Size: 10-40 m
– Shape: ovoid with pseudopodium
– Basic structure: cytoplasm, vesicular nucleus
(chromatin granules, nuclear membrane,
karyosome)

14. • Cyst
– Size: 10-20 m
– Structure: cyst wall, 1-4 nuclei, chromatoid
body
– Physiological function:
• The stage of discharge
• Resistant to external surroundings
• The infective stage

18. Main Points of Life Cycle
• Cycle: cyst—trophozoite—cyst
• Host: human being
• Lodgment: large intestine
• Infective stage: 4 nuclei cyst
• Infective route: mouth

19. Pathogenesis
• Pathogenic factor
– Virulence
– Species:
• E.histolytica (pathogenic species)
• E.dispar (non-pathogenic species)
– Immunity of host
– Bacteria flora

20. • Mechanism: contact lysis
• Pathology: flask-like ulcer
• Clinical manifestation
– Non symptomatic carriers
– Intestinal amebiasis: dysentery, colitis
– Extraintestinal amebiasis: liver abscess

23. Diagnosis
• Etiological diagnosis:
– Stool examination of cyst or trophozoite
– Sigmoidoscopy or aspiration
– Immunological diagnosis

24. Epidemiology
• Cosmopolitan: 110 population
• China: 3%~10%; Rural area>urban
• Source of infection: carriers
• Transmit route: water contamination
• Insects: fly, cockroaches

25. Prevention and Control
• Patients and carriers:
– Intestinal amoebiasis —metronidazole
– Extra~ amoebiasis —diloxanide
• Water & nightsoil control
• Insect vector control
• Personal hygienic health education

26. Plasmodium

27. Introduction
• Most important tropical disease
– 300 million cases with one million deaths world
wide in 1999;
– 30 million cases before liberation and 24000
cases reported with 39 death in 2000 in china;

28. • 4 species infecting human
– Plasmodium falciparum(恶性疟原虫)
– Plasmodium vivax(间日疟原虫)
– Plasmodium malariae(三日疟原虫)
– Plasmodium ovale(卵形疟原虫)

29. Life Cycle & Morphology
• Cycle in human (intermediate host)
– Exoerythrocytic stage(红细胞外期)
– Erythrocytic stage(细胞内期)

31. 红细胞外期(肝细胞内增殖)
Exo-erythrocytic cycle
（速发型）
子孢子 红外裂殖体 裂殖子
sporozoite E-E Schizont Merozoite
（迟发型P.v.）
进入红细胞
P.v. 8d; P.f. 6d; P.m. 12d

32. 红细胞内期(RBC内增殖)
Erythrocytic cycle
•发育：环形滋养体 大滋养体
(Ring form) (Trophozoite)
•增殖：早期裂殖体(Immature schizont)
RBC内发育
成熟裂殖体(子) 配子体形成
(Mature schizont) M吞噬

34. Scanning electron micrograph of Plasmodium-infected
red blood cells. One cell has burst open, releasing merozoites

35. P.v P.f P.m P.o

36. 红内期周期
•P.v. 48h
•P.f. 36-48h
•P.m. 72h
成熟裂殖体内裂殖子数和形态
•P.v. 12-24个，不规则
•P.f. 8-36个，不规则
•P.m. 6-12个，菊花状

37. 配子体形成
(Gametocyte form)
• 红内期裂殖子 雌雄配子
体
P.v. 2-3d
P.f. 7-10d
• <12个/mm3不能传播

38. 被寄生RBC的变化
•P.v. 胀大 薛氏小点
•P.f. 正常 茂氏点
•P.m. 正常 西门氏点

39. 疟原虫对RBC的选择
•P.v. 幼稚红细胞
•P.f. 各种红细胞
•P.m. 衰老红细胞

40. • Cycle in female anopheline mosquito
(definitive host)

42. 蚊体内发育(有性)
Grouth in the mosequito
雌配子体
Gametocyte 雌雄配子 受精
雄配子体 (Gametogony)
动合子Ookinete 合子
Zygote
卵囊Oocyst（内含子孢子Sporozoite）

43. 疟原虫发育过程
Sporozoite Schizont 子 Ring form Trophozoite
Oocyst 吞噬 merozoite Schiont
Ookinete Zygote Gamete Gametocyte(female/male)
(动合子) (合子) (配子) (配子体)

45. • Infective form: Sporozoite
• Period of one erythrocytic stage:
– P.V 48h; P.M 72h; P.F 36-48h
• Resting stage of sporozoite of P.V & P.O:
– Hypnozoite (brady sporozoite) in liver cell

46. Morphology

47. P.v P.f P.m P.o

48. Pathogenesis
• Primary attack
– Infected erythrocyte rupture 
products of schizont, stimulate the release of
cytokines (TNF)  paroxysm (shiver, fever,
sweat)

49. Scanning electron micrograph of Plasmodium-infected
red blood cells. One cell has burst open, releasing merozoites

50. • Relapse:
– It is a recurrence that taken place after complete
initial clearing of the erythrocytic infection and
implies reinvation of the blood stream by
merozoites from activated hypnozoites in liver.

51. • Recrudescence
– It is a recurrence of symptoms in a patient
whose blood stream infection has previously
been at such a low level as not to be clinically
demonstrable or cause symptoms.

52. Complications
• Anemia
– Hemolysis of infected erythrocytes
– Hypersplenism
– Autoimmunization of uninfected erythrocytes
– TNF-
• Splenomegaly:
• Malarious nephrosis
• Cerebral malaria

53. Erythrocyte, parasitized by Plasmodium falciparum,
showing surface knobs.

54. Diagnosis
• Parasitological diagnosis:
Parasite; Species; Density
– Thin blood films (species identification)
– Thick blood films

55. • 2. Immuno-diagnosis
– Specific antibody detection
 past malaria
– Antigen detection
– Specific DNA or RNA detection

56. Immunity
• Congenital immunity
– Duffy-negative erythrocytes are resistant to P.v
in West Africans
• Premunition
– The protective immunity persists while the
malaria parasites are still in the host.

57. • Evasion of immunity: An ability of malaria parasite
to evade host immunity.
• Possible mechanism of evasion
– 1) Antigenic variation
– 2) Sequestration (avoiding exposure to immune
effector mechanisms)
– 3) Poor immunogenicity of its antigens (analogy
exists between parasitic antigens and host molecules)

58. Treatment
• 1. Classes of antimalarial drugs
– 1) Blood schizonticides (quinine; chloroquine;
artemisinin; mefloquine; sulfadoxin-pyrimethamine)
– Effect on erythrocytic stage, use for acute attack

59. P-aminobenoic acid
(PABA)
+
dihydropteridine
Dihydrofolate
(folic acid)
Tetrahydrofolic acid
(folinic acid)
Purines and Pyrimidines
Nucleinic acid
ANTI FOLIC ACID
Sulfone
sulfanilamide
ANTI FOLINIC ACID
diguanides
diaminopyrimidines

60. – 2) Tissue schizonticides (Primaquine)
– Effect on the stages in liver (including
hypnozoite), use for prevent relapse (radical cure)
of P.v or P.o malaria

61. • 2. Choice of drugs
– 1) Treatment of vivax, malariae, ovale and
chloroquine-sensitive falciparum malaria:
chloroquine
– 2) Radical cure of vivax or ovale malaria:
chloroquine + primaquine
– 3) Treatment of chloriquine-resistant falciparum
malaria: artemisinin or mefloquine or quinine

62. Transmission and Prevention
• 1. Factors of transmission
– 1) Infected human (gametocyte-bearing)
– 2) Suitable species of anopheles (60 species are
considered to be vectors of malaria, major
vectors in China: A. sinensis, A. minimus)

63. – 3) Resistance of Anopheles to insecticides of
resistance plasmodium to antimalarial drugs.
– 4) Susceptible population
– 5) Other transmission mode: by transfusion,
syringe, congenital transmission

64. • 2. Prevention: breaking the human-mosquito-human
cycle
– 1) Control of the source of infection by
chemotherapy
– 2) Control of transmission route:
• residual insecticides, avoidance of infected mosquitoes
(bed nets impregnated with permethrin; mosquito
repellents (diethyl-metatoluamide)

65. – 2) Chemoproplylaxis
taking suppressive drugs, beginning one week
before travel to endemic area and continuing
until 6 weeks after return
– 3) Malaria vaccines

66. Flagellate
Phylum sarcomastigophora
Class zoomastigophorea

67. Leishmania donovani
杜氏利什曼原虫

68. General Introduction
• Zoonotic parasite
• One of the 5 major parasitic diseases
• Endemic northern to Yangtse river
• 0.5 million patients before 1949
• Basically eradicated in 1958

69. Visceral leishmaniasis has a wide geographic distribution.

70. Morphology
• Amastigote (leishman-donovan body):
– Human phase, reside in macrophage
– Very, very minute elliptical body
– No free flagellum
– Nucleus: deep red, located at one side
– Cytoplasm: blue (after right stain)
– Kinetoplast: basal body; rhizoplast

72. Leishmania amastigotes, bone marrow aspirate, Giemsa stain

73. • Promastigote:
– Vector phase
– Reside in the gut of sandfly
– Spindle shaped with 1 free flagellum
– Nucleus; cytoplasm; kinetoplast; basal body;
rhizoplast
– Chrysanthemum-like in culture medium

76. Main Points of Life Cycle
• Host: man and sandfly
• No sexual development in the host
• Residing site: macrophage
• Infective stage: promastigote
• Infective route: inoculation of sandfly
• Reservoir host: dog
• Infection could also via transfusion

77. Clinical Feature
• Irregular, long term fever
• Skin pigmentation—Kala-azar (india)
• Very poor prognosis: die within 1-2 year
without treatment
• Reason: lack of immunity after infection;
• But may gain sterilizing immunity
after effectively cured

78. Clinical Manifestation
• Hepatosplenomegaly
• Pancytopenia (hypersplenofunction,
immune lysis)
• Epistaxis (nosebleed)
• Nephrosis: albuminuria, hematuria
• Skin lesion: PKDL
• Enlargement of lymphaden

80. Cutaneous leishmaniasis of the face

81. Laboratory Diagnosis
• Etiological diagnosis
• Puncture smear
– Bone marrow: safe, of first choice
– Lymphaden: treatment evaluation
• Skin biopsy
• Tissue cultivation
• Animal inoculation
• Probe test: DNA or McAb

82. Epidemiology
• Cosmopolitan: Asia, Africa, Latin, America
• Distribution in China—3 types of areas

83. • Plain type
– Shangdon, dom. P.sinensis
• Hilly type
– Qinghai, wild P.sinensis
• Desert type
– Xinjiang, wild P.sinensis

84. The infection is transmitted by various species
of Phlebotomus, the sand fly.

85. Epidemic Links
• Source of infectin: patients and dogs
• Route of infection: phlebotomus spp.
• Susceptible population: all human
beings ( but potent immunity
developed after cure)

86. Control
• Treatment of patients:
• Sodium stibogluconate
• Kill infected dogs
• Eradicate sandfly: weak points
– Limited flying capacity
– Long breeding course
– Short seasonal prevalence
– Sensitive to insecticide

87. Reasons for a Successful
Control in China
• Free charge of treatment
• Potent immunity after being cured
• Large production effective drug
• Weak points of sandfly

88. Giardia lambia
蓝氏贾第鞭毛虫

89. Morphology
• Trophozoite
– Like badminton racket / “gost face”
– 2 discs
– 2 nuclei
– 4 pairs of flagella
– Axostyles

90. G.lamblia trophozoite

92. Another example of a Giardia lamblia
trophozoite. The two nuclei are easy to see in
this image.

93. • Cyst
– Ellipsoid
– Wall
– 4 nuclei
– Shrunken cytoplasm

94. Giardia lamblia
cyst
1 cyst containing 4 nuclei, rest of flagella
and sucking disc.

95. The nuclei and axostyles are clearly visible.

97. Main Points of Life Cycle
• Host: human being
• Residing site: small intestine
• Infective stage: 4 nuclei cyst
• Infective route: mouth

98. Clinical aspects
• Vomiting
• Flatulence
• Diarrhea
• Malabsorption syndrome
• Cholecystitis

99. Diagnosis
• Examination of stool for trophozoite or cyst
• Duodenal aspiration

100. Epidemiology
• Cosmopolitan
• Source of infection: carriers and patients
• Transmission route: faeces----mouth
• Susceptible population: traveler, AIDS
patients, homosexual population

101. Prevention and Control
• Patients and carriers: metronidazole
• Water & nightsoil control
• Insect vector control (fly, cockroach)
• Personal hygienic health education

102. Opportunistic Protozoa

103. Opportunistic Parasite
• Parasites which are not normally pathogens
but become so due to impairment of host
resistance.
• These are assuming increasing clinical
importance in AIDS epidemic.
• Opportunistic protozoa
– Toxoplasma gondii, Giadia lamblia, etc.

104. Toxoplasma gondii
刚地弓形虫

105. General Features
• A world wide distribution：1/3 population
• Opportunistic parasite
• Intracellular parasite
• Zoonotic parasite

106. Life Cycle and Morphology
• Two host pattern with alternation of
generation
• Definitive host: cat (acts also as I.H.)
• Intermediate host: human being and other
animals (herbivores, carnivores, omnivores)

107. Development in Cat
• Intestinal phase (sexual and asexual stage)
Schizogony merozoites (schizont)
Gametogony: micro and macrogametocyte 
micro and macrogamete  zygote  oocyst
Sporogony: sporozoites (mature oocyst)
(outside of the cat)

108. Development in Man
• Extraintestinal phase (asexual)
– Infective stage
• Oocyst
• Tachyzoite
• Cyst
• Infective route: mouth
• Residing site: tissue cells

110. T. gondii: lysis of a THP-1 cell with release of
tachizoites in culture.

111. Tachyzoites of Toxoplasma gondii
in macrophages of mouse in peritoneal exudate. (SEM)

112. Tachyzoites of Toxoplasma gondii
in macrophages of mouse in peritoneal exudate.
(SEM)

113. In cell cultures, T.gondii proliferates to form a
pseudocyst of 8-20 parasites.

114. T. gondii: tissue cysts, 100-300 µm, may
contain up to 3 000 bradyzoites.

115. Pathogenesis
• Acquired toxoplasmosis: eye lesion (uveitis,
choroiditis, choroidoretinitis);
lymphadenopathy
• Congenital toxoplamosis:
– Abortion;
– Still birth (abnormities): hydrocephalus,
mental retardation

116. Pathogenesis
• Toxoplamosis in immunoincompetent hosts
– Encephalitis
– Pneumonitis
– Myocarditis
– Hepatitis, etc.

117. Diagnosis
• Immunological diagnosis of specific IgG or
IgM (first choice), eg:
DT, ELISA, IFA, IHA, etc
• Histological exams
• Animal inoculation
• PCR

118. Main Points
• Multi-cellular parasitism
• Transmission mode
– Congenital
– I.H.  I.H
– D.H  I.H
– I.H  D.H

119. Epidemiology
• Cosmopolitan
• France: 45-85%
• Africa: 46%
• USA : 25-36%
• China : 30%

120. Epidemiological Factors
• Consuming raw or undercooked meat
containing cyst
• Contact with cats ( oocyst consumption)

121. Prevention Control
• Drug: pyrimethamine +sulfadiazine
spiramycin (for pregnant women)
• Avoid contact with the cats ?
• Avoid eat raw or undercooked meat