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1. Author(s): Vernon Carruthers, Ph.D., Cary Engleberg, M.D., D.T.M.&H., 2009
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3. PARASITOLOGY
M1 Infectious Diseases Sequence
Vernon Carruthers
Cary Engleberg
Spring 2009

4. What do you need to learn
for this course?
• Recognize the names of pathogens
associated with characteristic diseases
(Don t memorize names or spellings)
• Remember the key features of the life
cycles (i.e., how do the parasite get from one
host to the next?)
• Remember the main mechanisms of
disease (i.e., how does damage to the host
occur?)
3

5. Definitions
• zoonosis
• enzootic ~ endemic
• epizootic ~ epidemic
• reservoir
• vector
4

6. Major Human Parasites
Protozoan (single-celled) parasites
Low branching protozoa (Entamoeba)
Kinetoplastids (African trypanosomes, Leishmania)
Apicomplexa (Plasmodium, Toxoplasma)
Fungus-like protozoa (Microsporidia)
Metazoan (multicellular) parasites
Nematode (Onchocerca or hookworm)
Trematode (Schistosoma)
Cestode (Tapeworm e.g., Echinococcus)
5

7. Microsporidia
Parasites on the
Tree of Life
Apicomplexan
Metazoans
Entamoeba*
Kinetoplastids
Giardia
*low-branching eukaryote
Sandy Baldauf / Boris Striepen
6

8. Parasite Diversity
100m
10m
1m
10cm
1cm
1mm
100mm
10mm
1mm
N
N
Microsporidia Apicomplexa Kinetoplastid Trematode Cestode Nematode
Protozoa Metazoa
7
Vernon Carruthers

9. Global Morbidity and Mortality from
Parasitic Diseases
* * *
1700
*Annual
West Nile Virus <0.5 <0.01 <0.3
8
Source Undetermined

10. New Trends in Emerging
Infectious Diseases
9
Jones et. al., Nature Feb 2008

11. Factors influencing the geography
of parasitic infections
• Local ecology
– vectors
– reservoirs (animal and human)
– local habitats
• Local socioeconomic conditions
– sanitation
– exposure to vectors
– untreated carriers
10

12. Protozoal
Infections
11

13. Classification of protozoa
Entamoebae
(shapeless)
Source Undetermined
Flagellates
Alveolates
Source Undetermined
(sub-membrane
cytoskeleton confers Apicomplexa
a fixed shape) (Sporozoa)
Source Undetermined
(Ciliates) 12

14. Outline of protozoal diseases
Intestinal protozoal infection
Systemic protozoal infection
13

15. Outline of protozoal diseases
Intestinal protozoal infection
-Invasive (dysentery/bloodstream invasion)
entamoeba * Entamoeba histolytica
-Non-invasive (watery diarrhea/weight loss)
dinoflagellate * Giardia lamblia (G. intestinalis)
apicomplexa * Cryptosporidia and Cyclospora
* microsporidia
Systemic protozoal infection
14

16. Amebiasis
• Entamoeba - an enteric amoeba, i.e., not
free-living.
• histolytica - human invasion by the
parasite involves tissue lysis (histo-lytica)
15

17. E. histolytica - parasitic forms
Cary Engleberg
16

18. Trophozoites in Ulcer
with Ingested Red Blood
Cells
William Petri
17

19. Entamoeba histolytica -- life cycle
• Humans are the only reservoir excreting
amoebic cysts
• Cysts resist environmental conditions
• Fecal-oral transmission (food, water)
• In response to gastric acid, ingested cysts
release trophozoites in the upper intestine
• Trophozoites invade the large intestine and
replicate by fission.
• Trophozoites that reach the lower colon
encyst again.
18

20. Source Undetermined Source Undetermined
Trophozoite in stool Cyst in stool
19

21. Entamoeba histolytica -- pathogenesis
• Trophozoites disrupt mucus layer
• Key virulence factors:
– amebic lectin: binds parasite to galactose-
containing sugars on host cells
– amoebapores: adherence-dependent cytolysis
– cysteine protease: cleaves preIL-1β to IL-1β which triggers
NF-kB and pro-inflammatory cytokines; also cleaves antibodies
and C3
• Trophozoites ingest human cells
• Colonic ulceration
20

22. Risk Factors for Amebiasis in the
United States
• Hispanic/Asian/Pacific Islanders - 50% of U.S. cases
reported to CDC
• Travelers - 0.3% incidence in one study
• Institutions for mentally retarded
• Men who have sex with men
• Men - 90% amebic liver abscesses in men (male mice
also more susceptible, in part because of lower IFNγ and
fewer functional NKT cells)
21

23. Carbohydrate
side-chains terminating
in gal - galNAc ( )
22
Cary Engleberg

24. 1. Adherence
Ameba
Intestinal Lumen 2. Lectin
Signal
4. Phagocytosis
and Invasion
3. Cell killing
23
William Petri

25. TUNEL Stain Demonstrates Apoptosis at
Sites of Amebic Invasion of Mouse Colon
William Petri
24

26. Histopathology of amebiasis
Tissue Destruction
in Amebic Colonic
Ulcer
William Petri
Classic Flask-Shaped Ulcers (side view) 25

27. Source Undetermined
26

28. Source Undetermined
27

29. Amebiasis - clinical
syndromes
• Intestinal
– Ranges from asymptomatic to chronic
diarrhea to amebic dysentery
• Extraintestinal
– amebic liver abscess
– other metastatic foci (e.g., brain)
Dx: identification of trophozoites or cysts
in the stool, stool antigen tests, serology 28

30. Two microscopically
indistinguishable Entamoeba sp.
• E. histolytica
– invades tissues
– should always be treated, even in asx
patients
• E. dispar
– is non-pathogenic, even in AIDS
– should not be treated
29

31. Treatment of amebiasis
• The parasites in two locations are
treated sequentially with two drugs
– For invasive forms: metronidazole
– For luminal forms: diiodohydroxyquin,
paromomycin, diloxanide furoate
• Do not treat asymptomatic intestinal
E. dispar infection
30

32. Giardiasis
31

33. Giardiasis - life cycle
Trophozoite Cyst
Giardia
• G. lamblia is a zoonosis (infected small mammals pass
cysts and contaminate surface waters)
• Waterborne transmission is most common, but can
also be spread person-to-person by young children
(e.g., day-care centers)
• Ingested as cysts
• Excystation of the trophozoite and attachment to the
mucosa occurs in the upper small intestine. 32
Vernon Carruthers

34. Source Undetermined Source Undetermined
Trophozoites in duodenum Cyst in stool
33

35. Giardia pathogenesis
• Parasites elicits localized
hypersensitivity
• Intestinal villi become blunted
• Malabsorption develops
34

36. Dorsal
Suction
Disc
Ventral
Source Undetermined 35

37. Giardia - clinical features
• Acute, self-limited diarrhea
• Chronic diarrhea with
malabsorption, steatorrhea, and
weight loss
• Chronic asymptomatic cyst
passage
Dx: stool antigen testing, stool examination,
duodenal aspirate.
36

38. Giardiasis - treatment
• Metronidazole (or nitazoxanide)
Giardiasis - prevention
• Filtration of water
• Heating water to >50oC
• 2% iodine x 30 minutes
37

39. Generalizations about other
intestinal protozoa
(Cryptosporidium, Cyclospora, Microsporidia)
• All acquired by fecal-oral route
• All grow abundantly inside of mucosal
cells
• All cause watery diarrhea, cramps,
anorexia (not inflammatory) -
pathogenesis uncertain
• All require special stains or examinations
of stool for dx. 38

40. Cryptosporidium in tissue
Organisms attached Intestinal organisms
to an intestinal villus by scanning EM
Source Undetermined Source Undetermined
39

41. Cryptosporidium parvum
• Associated with-
– prolonged self-limited diarrhea in
immunocompetent individuals
– traveler s diarrhea
– chronic, unrelenting diarrhea in AIDS
• Usual acquired from
– drinking water (e.g., Milwaukee, 1993)
– swimming pools
• Relative chlorine resistance
40

42. Number of cryptosporidiosis cases, by
date of onset, Delaware Co., Ohio, Jun–Sep 2000
Center for Disease Control and Prevention
• Relative risk of swimming at a private swim club = 42.3
(12.3–144.9)
• At least 5 fecal accidents witnessed 41

43. Cryptosporidium
Source Undetermined Source Undetermined
Iodine stain of stool Acid-fast stain of stool
42

44. Treatment of
cryptosporidiosis
• Supportive (rehydration,
antimotility agents)
• No FDA-approved rx
• Nitazoxanide?
43

45. Cyclospora
Source Undetermined
44

46. Cyclospora
• Food and waterborne transmission
– 1996-97 outbreaks associated with Guatemalan
raspberries shipped to U.S.
• Also replicates within mucosal cells
• Diarrhea may persist for 1-2 months
without treatment
• Trimethoprim/sulfa x 7 days is effective
therapy (unlike Cryptosporidium)
45

47. Microsporidia
• Primitive fungi that were initially
thought to be protozoa
• Long recognized as animal pathogens
– human cases in AIDS
– recent human cases also seen in
immunocompetent persons
• Hundreds of species identified
46

48. Louis Weiss
Ex, exospore Louis Weiss
En, endospore
AD, achoring disc
PT, polar tube 47
Sp, sporoplasm

49. Explosive Discharge of the Invasion
Tube
• 4-30 coils depending on spp
• Stimulus varies depending on
spp, can be pH shift,
dehydratioin/rehydration,
mucin, UV, etc
• Stimulus increases osmotic
pressure, water influx
48

50. Outline of protozoal diseases
Intestinal protozoal infection
Systemic protozoal infection
50

51. Outline of protozoal diseases
Intestinal protozoal infection
Systemic protozoal infection
- Malaria (Plasmodium sp.) (RBC infection
and fever)
apicomplexa - Babesiosis (Babesia sp.)
- Toxoplasmosis (T. gondii) (Intracellular
- Leishmaniasis infections)
dinoflagellates
- Others:
African trypanosomiasis (sleeping sickness)
American trypanosomiasis (Chagas disease)
51

52. Toxoplasmosis
52

53. Toxoplasma Features
• Apicomplexan parasite (similar
to Cryptosporidium,
Cyclospora and Plasmodium)
53

54. Gliding Motility of Apicomplexa
Cary Engleberg
DanielCD, wikimedia commons
54

55. Entry of Apicomplexa into cells
Cary Engleberg
55

56. • Cats infected by
predation
• 107 oocysts passed
in feces
• Stable in soil/water
for months
• Either indirect thru
intermediate
host or direct via
food/water
Ingests
• Vertical Contamination
of food/water
cysts in
raw or
transmission during undercooked
meat
pregnancy
Center for Disease Control and Prevention
56

57. McGill University Department of Medicine 57

58. Toxoplasmosis - clinical
syndromes
• acute acquired toxoplasmosis
• congenital toxoplasmosis
• ocular toxoplasmosis
• cerebral toxoplasmosis (AIDS)
58

59. congenital toxoplasmosis
• 30-40% transplacental if mother is
infected during pregnancy
• 60% of infected newborns are
asymptomatic (but later show
chorioretinitis)
• affected infants may have
hydrocephalus, hepatosplenomegaly,
jaundice, fever, anemia, pneumonia
59

60. Source Undetermined
60

61. Source Undetermined
61

62. Source Undetermined
Source Undetermined
62

63. Source Undetermined
63

64. Diagnosis of toxoplasmosis
• direct identification is difficult
• culture is not routinely done
• serology
– IFA or ELISA
– single high IgM or very high IgG level
– seroconversion not reliable in AIDS
• clinical features and response to rx
64

65. Treatment of toxoplasmosis
When RX is indicated . . .
sulfadiazine + pyrimethamine*
OR
clindamycin + pyrimethamine*
* plus folinic acid
65

66. Malaria
66

67. Source Undetermined
67

68. Center for Disease Control and Prevention
68

69. Asexual replication
Exoerythrocytic
"ring"
cycle
form
trophozoite
Sporozoites
released from
mosquito salivary
glands invade
merozoites
hepatocytes
released
Erythrocytic
w
ithin 30 mins.
cycle
schizont
Male and
f
emale
ruptured
g
ametocytes
RBC releases
merozoites
Sexual replication
• Fertilization and invasion of mosquito gut
• Infected cell releases sporozoites, which
migrate to the salivary glands.
69
Cary Engleberg

70. Asexual stages
Exoerythrocytic
cycle
Erythrocytic
cycle
6-15 days 2-3 days
70
Cary Engleberg

71. Sporozoites and hepatic
schizont
McGill University Department of Medicine
McGill University Department of Medicine 71

72. Center for Disease Control and Prevention
72

73. Center for Disease Control and Prevention
73

74. Center for Disease Control and Prevention
74

75. Plasmodium species
ERYTHROCYTIC HEPATIC
SPECIES CYCLE LATENCY RECURRENCES
P. falciparum 48 hrs no no
P. vivax 48 hrs yes yes
P. ovale 48 hrs yes yes
P. malariae 72 hrs no yes
75

76. Imported malaria cases, by species and
interval between date of arrival and onset of
illness — U.S., 1992
180
140
No. 100
of
cases 60
20
P. vivax
<1 P. malariae
1-2 P. ovale
3-5
6-12 P. falciparum
Months >12 76
Vernon Carruthers

77. Imported malaria cases, by year, 1973-2000, U,S.
2000
1800
1600 ~ 1/2 are
imported
1400
from
1200 Africa
1000
800
600
400 U.S. civilians
200 Total
0
Year
Source Undetermined
77

78. Stable and unstable malaria
transmission
stable unstable
continuous epidemic
transmission malaria
Clinical disease children all ages
Mortality children all ages
Enl. Spleen rate (2-9 yrs) >10% <10%
Immunity among adults high low
Parasitism rate high low
78

79. Malaria - clinical features
• paroxysms associated with
synchronous release of merozoites
from RBCs
– Infected RBCs release substances that
stimulate the release of TNFα and IL-1 from
host cells
– rigorous chills, fever, myalgia, severe
headache ± GI symptoms (5-6 hours)
– profuse sweating and exhaustion (2-3 hours)
79

80. Malaria - clinical features
• immunologically-mediated
hematologic changes
– anemia
– thrombocytopenia
– leukopenia
80

81. Enhanced virulence of P.
falciparum
• merozoites can enter RBCs of any age
• parasitemias reach very high levels
• adhesin proteins deployed on infected
RBCs (trophozoites and schizonts)
– attachment to venular endothelial cells (e.g., via
ICAM-1)
– reduced blood flow in small vessels -->
microinfarction, hemorrhage
81

82. Adherent P. falciparum schizonts
KNOB
J.D. Maclean, McGill Univ.
J.D. Maclean, McGill Univ.
Schizonts adhering to retinal blood vessels
82

83. Source Undetermined
83

84. Source Undetermined
84

85. Antimalarial treatment
• based on species and location acquired
– chloroquine-sensitive species
rx: chloroquine (blocks heme iron
detoxification)
– Chloroquine ® P. falciparum
Rx (quinine + doxycycline) or Malarone®
• Add primaquine for P. vivax and P. ovale
85

86. Hemezoin Formation: Eating
the Host From the Inside Out
• Hemeglobin 300 mg/ml inside RBC!
• Parasite digests hemeglobin for
nutrients and to create room for growth Source Undetermined
Source Undetermined
• Problem: Free heme is extremely
toxic because generates oxygen
radicals
• Solution: sequester in hemezoin
crystals! Tulane University
Madame Curie Bioscience Database
• Most malaria drugs interfere with
hemezoin formation 86

87. Sequence of the
creation of
hemozoin in red
cell removed
87

88. Based on what you have just learned,
suggest three simple strategies to
prevent the propagation of malaria.
1) _________________
2) _________________
3) _________________
88

89. Strategies to prevent malaria
1) mosquito control (insecticides, remove habitats)
2) mosquito protection (nets, screens, repellants)
3) mass treatment
• vaccines (immunity is species and stage-specific)
• release of genetically altered mosquitoes
89

90. Leishmaniasis
90

91. Center for Disease Control and Prevention
91

92. Source Undetermined
92

93. Source Undetermined
Leishmania are intracellular parasites that reside
in macrophage phagolysosomes 93

94. Source Undetermined
Chronic skin ulcerations with raised edges at site of sand fly bite.
(organisms do not survive well at 37oC, therefore, they don t tend to disseminate)
94

95. Source Undetermined
95

96. Source Undetermined
96

97. Cary Engleberg Cary Engleberg
L. braziliensis lasts longer and may
recur later with destructive lesions in
the nose and throat
97

98. McGill University Department of Medicine
98

99. J.D. Maclean, McGill Univ.
99

100. Visceral leishmaniasis -
Kala-azar
• Infection of macrophages in the liver, spleen
and lymph nodes
• Fever, malaise, weight loss, abdominal pain
• Dx: aspirate of bone marrow, spleen or liver;
serology
• Outcome: 75-90% fatal if untreated (death 2o
to bacterial pneumonia)
100

101. Contributed from H. Zaiman ©1996
101

102. Additional Source Information
for more information see: http://open.umich.edu/wiki/CitationPolicy
Slide 7: Sandy Baldauf / Boris Striepen
Slide 8: Vernon Carruthers
Slide 9: Source Undetermined
Slide 10: Jones et. al., Nature Feb 2008
Slide 13: Source Undetermined
Slide 17: Cary Engleberg
Slide 18: William Petri
Slide 20: Source Undetermined
Slide 23: Cary Engleberg
Slide 24: William Petri
Slide 25: William Petri
Slide 26: William Petri
Slide 27: Source Undetermined
Slide 28: Source Undetermined
Slide 33: Vernon Carruthers
Slide 34: Sources Undetermined
Slide 36: Source Undetermined
Slide 40: Sources Undetermined
Slide 42: Center for Disease Control and Prevention, MMWR 2000; 50:406, http://www.cdc.gov/mmwr/preview/mmwrhtml/ss5108a1.htm
Slide 43: Sources Undetermined
Slide 45: Source Undetermined
Slide 48: Louis Weiss
Slide 54: Cary Engleberg; DanielCD, Wikimedia Commons, http://commons.wikimedia.org/wiki/File:AmericanTank.jpg, CC:BY-SA,
http://creativecommons.org/licenses/by-sa/3.0/
Slide 55: Cary Engleberg
Slide 56: Center for Disease Control and Prevention, Alexander J. da Silva, PhD / Melanie Moser, CDC PHIL #3421, http://www.cdc.gov
Slide 57: McGill University Department of Medicine, http://www.medicine.mcgill.ca/tropmed
Slide 60: Source Undetermined
Slide 61: Source Undetermined
Slide 62: Sources Undetermined
Slide 63: Source Undetermined
Slide 67: Source Undetermined
Slide 68: Center for Disease Control and Prevention, James Gathany, CDC PHIL #7950 http://www.cdc.gov
Slide 69: Vernon Carruthers
Slide 70: Vernon Carruthers
Slide 71: McGill University Department of Medicine, http://www.medicine.mcgill.ca/tropmed (Both Images)
Slide 72: Center for Disease Control and Prevention

103. Slide 73: Center for Disease Control and Prevention
Slide 74: Center for Disease Control and Prevention/ Steven Glenn, CDC PHIL #5941
Slide 76: Source Undetermined
Slide 77: Source Undetermined
Slide 82: J.D. Maclean, McGill University (Both Images)
Slide 83: Source Undetermined
Slide 84: Source Undetermined
Slide 86: Source Undetermined; Undetermined; Tulane University, http://www.tulane.edu/~wiser/malaria/B-heme.gif ; Madame Curie Bioscience Database,
http://www.landesbioscience.com/curie/
Slide 87: Source Undetermined
Slide 91: Center for Disease Control and Prevention, Frank Collins, James Gathany, CDC PHIL #10275, http://www.cdc.gov
Slide 92: Source Undetermined
Slide 93: Source Undetermined
Slide 94: Source Undetermined
Slide 95: Source Undetermined
Slide 96: Source Undetermined
Slide 97: Cary Engleberg
Slide 98: McGill University Department of Medicine, http://www.medicine.mcgill.ca/tropmed
Slide 99: J.D. Maclean, McGill University
Slide 101: Contributed from H. Zaiman ©1996