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Parasitology Flashcards

1
Q

What is parasitism?

A

A close association between two species in which one benefits at the expense of the other

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2
Q

What is an ectoparasite?

A

Parasite living externally on host

Eg. fleas, ticks, leeches

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3
Q

What is an endoparasite?

A

Live in host body for significant part of lifestyle

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4
Q

What is a direct life cycle?

A

Involves only a single host species

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5
Q

What is an indirect life cycle?

A

Involves two or more host species

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6
Q

What are parasitic helminths?

A

Endoparasitic metazoan eukaryotes

  1. Nematodes
  2. Platyhelminthes
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7
Q

What are the two subphyla of platyhelminthes?

A
  1. Trematodes (flukes)

2. Cestodes (tapeworms)

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8
Q

Give four features of the nematode structure

A
  1. Cylindrical body
  2. Separate sexes
  3. Radial symmetry
  4. Non-cellular outer cuticle
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9
Q

How do nematodes invade the host?

A

Active invasion through skin penetration

From soil contaminated with human faeces infected with nematode eggs

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10
Q

What kind of helminth is a hookworm?

A

Nematode

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11
Q

Below which temperature will juvenile hookworms not develop?

A

17 degrees Celsius

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12
Q

Where do adult hookworms reside in the host?

A

Small intestine

Feed on blood

Larvae migrate to lungs, then coughed up and swallowed

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13
Q

Give two species of filarial nematode

A
  1. Wucheria bancrofti

2. Onchocerca volvulus

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14
Q

Where do adult W. bancrofti live?

A

Lymph nodes

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15
Q

Where do adult O. volvulus live?

A

Subcutaneous nodules

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16
Q

Where are W. bancrofti microfilaria released?

A

Peripheral cutaneous blood vessels

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17
Q

Where are O. volvulus microfilaria released?

A

Skin

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18
Q

What is the W. bancrofti vector?

A

Mosquito

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19
Q

What is the O. volvulus vector?

A

Blackfly

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20
Q

What pathology does W. bancrofti cause?

A

Elephantiasis

Lymphatic return is obstructed by inflammation so lymph builds up in ducts causing massive dilatation

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21
Q

What are the most commonly afflicted organs in W. bancrofti infection?

A
  1. Scrotum
  2. Legs
  3. Arms
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22
Q

At what time of day are W. bancrofti microfilaria present in the bloodstream?

A

At night, because mosquitoes are night-feeders

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23
Q

What pathology does O. volvulus cause?

A

River blindness

Microfilaria released in skin may invade eye and cause inflammation

Build up of fibrous tissues causes blindness

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24
Q

What are Wolbachia?

A

Obligate intracellular bacteria

Parasites of W. bancrofti and O. volvulus

Mutualistic symbiotic association

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25
What is the result of depletion of Wolbachia in parasite infection?
Worm cell death by apoptosis of reproductive cells, developing embryos, microfilariae and developing larvae
26
What type of helminth is a schistosome?
Trematode
27
What type of helminth is a tapeworm?
Cestode
28
What is the head of a tapeworm called?
Scolex
29
What is the external covering of a tapeworm?
Tegument
30
Where are tapeworm reproductive organs located?
Stobila Consist of several proglottids, each containing one set of reproductive organs of both sexes
31
How many hosts does the tapeworm life cycle require?
Two
32
What is an oncosphere?
Embryogenesis of larva within egg
33
What is the definitive host of Taenia saginata?
Humans
34
What is the intermediate host of Taenia saginata?
Cattle
35
What symptoms does Taenia saginata infection cause?
1. Dizziness 2. Abdominal pain 3. Headache 4. Sensitivity to touch 5. Nausea 6. Diarrhoea/intestinal obstruction
36
How does Taenia solium infection occur?
Eating meat infected with cysticerci
37
What is cysticercosis?
Infection of both humans and pigs with larval stage of tapeworm Once ingested, eggs migrate from intestine to striated muscle, brain, liver and eye and form cysticerci
38
What is ocular cysticercosis?
Irreparable damage to eye
39
What is neurocysticercosis?
Cysts in brain Blindness, disequilibrium, sudden onset epilepsy Severe inflammation from dead cysticerci - fatal
40
What are the two major groups of protozoan parasites?
1. Kinetoplastida | 2. Apicomplexa
41
What class of parasite are trypanosomes?
Kinetoplastida
42
What pathology do African trypanosomes cause?
Human sleeping sickness
43
What pathology do South American trypanosomes cause?
Chagas' disease
44
What is the vector for Leishmania?
Blackflies
45
What is the kinetoplast?
Organelle containing extrachromosomal DNA?
46
What is the trypomastigote?
Extracellular flagellated form of trypanosome
47
What is the amastigote?
Intracellular unflagellated form of trypanosome
48
What morphological form do African trypanosomes produce?
Only trypomastigotes
49
What morphological form do Leishmania produce?
Only amastigotes
50
What morphological form do Trypanosoma cruzi produce?
Both trypomastigote and amastigote
51
Give four examples of apicomplexa
1. Babesia - babesiosis 2. Plasmodium - malaria 3. Cryptosporidium - cryptosporidiosis 4. Toxoplasma gondii - toxoplasmosis
52
Give two features of apicomplexa
1. Apicoplast | 2. Apical complex for host cell penetration
53
What is the definitive host of toxoplasma gondii?
Cat
54
What pathologies does toxoplasma cause?
1. Birth defects in humans | 2. Spontaneous abortion in sheep
55
How does T. gondii enter cells?
Active transport mediated by parasite cytoskeleton Locates within parasitiphorous vacuole
56
What kind of life cycle does Plasmodium have?
Indirect
57
What are the hosts of Plasmodium?
Definitive host = dipteran insect, eg. mosquito Intermediate host = vertebrates
58
What are the vectors of human malaria parasites?
Female anopheles mosquito
59
What is the only plasmodium species that sequesters in tissues?
P. falciparum
60
What causes cerebral malaria?
P. falciparum Sequestration in cerebral venules and capillaries
61
What are hypnozoites?
Dormant liver stages of P. ovale and P. vivax
62
What kind of individuals does P. ovale infect?
Duffy blood group negative
63
What is the only human species of malaria with a quartan life cycle?
P. malariae
64
Which malaria is zoonotic?
P. knowlesi
65
What are sporozoites?
Form released from mosquito salivary glands Enter host bloodstream and circulate to liver
66
What are merozoites?
Released from mature schizonts Invade red blood cells
67
What are schizonts?
Trophozoite inside hepatic cell as it grows in size and replicates its nucleus Rupture and release merozoites
68
What are some of the symptoms of malaria?
1. Anaemia 2. Splenomegaly 3. Hypoglycaemia 4. Metabolic acidosis
69
How does P. falciparum modify host cells?
Modifies surface of infected red blood cells Cells express parasite protein PfEMP1 Can adhere to endothelial cells due to knob-like projections Sequestration
70
What are the clinical features of cerebral malaria?
1. Convulsions 2. Impaired consciousness 3. Unrousable coma
71
What gene family encodes PfEMP1?
Var genes
72
Why does cerebral malaria cause coma?
1. Obstruction - impaired nutrient supply and waste removal 2. Cytokines - TNFα & IL-1 stimulates inflammation 3. Parasite toxins when RBC ruptures
73
What is the most likely malarial parasite toxin?
Glycosylphoshatidyl inositol (GPI) Functions as membrane anchor for merozoite surface proteins
74
How do macrophages recognise GPI?
Toll-like receptors
75
How does malaria break the integrity of the blood brain barrier?
PfEMP-1 binds to ICAM-1 on the endothelium of the BBB Secondary signalling causes changes in the cytoskeleton
76
How does malaria cause anaemia?
1. Destruction of parasitised red blood cells during merozoite replication 2. Destruction of uninfected red blood cells 3. Decreased erythropoiesis
77
How are red blood cells destroyed in infection?
1. Oxidation - reduced deformability 2. Complement binding 3. Adsorption of immune complexes and IgG These mechanisms target RBCs for destruction by intravascular haemolysis or macrophages
78
How does malaria cause acidosis?
Anaemia results in failure of oxygen delivery to tissues Increased lactate production
79
What type of individuals does P. vivax infect?
Duffy blood group positive
80
What causes sickle cell haemoglobin?
Val--> glu substitution in β-chain of haemoglobin
81
What is the link between sickle cell anaemia and malaria?
Individuals heterozygous for sickle cell trait are protected against malaria
82
How does sickle cell trait protect against malaria?
1. Enhanced sickling of parasitised red blood cells promotes increased removal by spleen 2. Parasite development impaired in HbS RBCs 3. Parasitised HbS RBCs express less PfEMP-1
83
What is the effect of glucose-6-phosphate dehydrogenase deficiency?
1. Affects parasite growth | 2. Promotes efficient phagocytosis of parasitised red blood cells
84
What HLA is associated with decreased malaria risk?
HLA-B53 Presents liver stage and sporozoite antigens to T cells
85
Give five features of the structure of trematodes
1. Dorsoventrally flattened body 2. Bilateral symmetry 3. Complex outer tegument 4. Lack body cavity 5. Usually hermaphrodite
86
What are blood flukes?
Schistosomes
87
What are the host of schistosomes?
``` Intermediate = snail Definitive = vertebrates ```
88
How do schistosomes reproduce?
Separate sexes Unique among trematodes
89
Where do adult schistosomes live in the host?
In blood vessels round gut or bladder
90
Which schistosome is zoonotic?
S. japonicum
91
Which schistosome is only found in man?
S. haematobium
92
What is the treatment for schistosomiasis?
Praziquantel
93
With which species of schistosome is eosinophilia seen?
1. S. haematobium | 2. S. mansoni
94
With which species of schistosome is IL-4 and IL-5 seen?
1. S. haematobium | 2. S. mansoni
95
With which species of schistosome is anti-schistosome IgE seen?
1. S. haematobium 2. S. mansoni 3. S. japonicum
96
Where is the schistosome immunity gene located?
Near TH2 cytokine cluster on human chromosome 5
97
What causes swimmer's itch?
Repeat exposure to non-human schistosomes
98
How does schistosomiasis cause nephrotic lesions?
Produces circulating antigens Form antigen/antibody immune complexes
99
What is the most obvious symptom of S. haematobium infection?
Haematuria
100
What cancer is schistosome infection associated with?
Bladder squamous cell carcinoma
101
What is the basic reproductive rate of macroparasites?
Number of next generation hermaphrodite/female worms that reach sexual maturity produced by a single worm
102
How is schistosomiasis controlled?
1. Chemotherapy 2. Vector control 3. Sanitation 4. Education
103
What is the treatment for intestinal nematodes?
1. Albendazole | 2. Mebendazole
104
What is the only successful anti-helminth vaccine?
Against cattle lung worm
105
What is the adaptive immune response to the liver stage of malaria?
Cytotoxic CD8 T cell
106
What is the adaptive immune response to sporozoites, merozoites and Plasmodium proteins?
Antibodies
107
How does malaria evade the immune system?
1. Complex life cycle with antigenic diversity 2. Different species 3. Different strains of each species 4. Different stages in life cycle
108
How does PfEMP-1 contribute to immune evasion?
1. Encoded by at least 50 var genes - antigenic diversity | 2. Causes sequestration to avoid destruction of infected RBCs
109
Why are women more susceptible to malaria during first pregnancy?
P. falciparum subpopulation expresses a PfEMP-1 that binds CSA, which is highly expressed in the placenta

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