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BOD > Parasitology > Flashcards

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
Q

What is the result of depletion of Wolbachia in parasite infection?

A

Worm cell death by apoptosis of reproductive cells, developing embryos, microfilariae and developing larvae

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26
Q

What type of helminth is a schistosome?

A

Trematode

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27
Q

What type of helminth is a tapeworm?

A

Cestode

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28
Q

What is the head of a tapeworm called?

A

Scolex

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29
Q

What is the external covering of a tapeworm?

A

Tegument

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30
Q

Where are tapeworm reproductive organs located?

A

Stobila

Consist of several proglottids, each containing one set of reproductive organs of both sexes

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31
Q

How many hosts does the tapeworm life cycle require?

A

Two

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32
Q

What is an oncosphere?

A

Embryogenesis of larva within egg

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33
Q

What is the definitive host of Taenia saginata?

A

Humans

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34
Q

What is the intermediate host of Taenia saginata?

A

Cattle

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35
Q

What symptoms does Taenia saginata infection cause?

A
  1. Dizziness
  2. Abdominal pain
  3. Headache
  4. Sensitivity to touch
  5. Nausea
  6. Diarrhoea/intestinal obstruction
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36
Q

How does Taenia solium infection occur?

A

Eating meat infected with cysticerci

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37
Q

What is cysticercosis?

A

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

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38
Q

What is ocular cysticercosis?

A

Irreparable damage to eye

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39
Q

What is neurocysticercosis?

A

Cysts in brain

Blindness, disequilibrium, sudden onset epilepsy

Severe inflammation from dead cysticerci - fatal

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40
Q

What are the two major groups of protozoan parasites?

A
  1. Kinetoplastida

2. Apicomplexa

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41
Q

What class of parasite are trypanosomes?

A

Kinetoplastida

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42
Q

What pathology do African trypanosomes cause?

A

Human sleeping sickness

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43
Q

What pathology do South American trypanosomes cause?

A

Chagas’ disease

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44
Q

What is the vector for Leishmania?

A

Blackflies

45
Q

What is the kinetoplast?

A

Organelle containing extrachromosomal DNA?

46
Q

What is the trypomastigote?

A

Extracellular flagellated form of trypanosome

47
Q

What is the amastigote?

A

Intracellular unflagellated form of trypanosome

48
Q

What morphological form do African trypanosomes produce?

A

Only trypomastigotes

49
Q

What morphological form do Leishmania produce?

A

Only amastigotes

50
Q

What morphological form do Trypanosoma cruzi produce?

A

Both trypomastigote and amastigote

51
Q

Give four examples of apicomplexa

A
  1. Babesia - babesiosis
  2. Plasmodium - malaria
  3. Cryptosporidium - cryptosporidiosis
  4. Toxoplasma gondii - toxoplasmosis
52
Q

Give two features of apicomplexa

A
  1. Apicoplast

2. Apical complex for host cell penetration

53
Q

What is the definitive host of toxoplasma gondii?

A

Cat

54
Q

What pathologies does toxoplasma cause?

A
  1. Birth defects in humans

2. Spontaneous abortion in sheep

55
Q

How does T. gondii enter cells?

A

Active transport mediated by parasite cytoskeleton

Locates within parasitiphorous vacuole

56
Q

What kind of life cycle does Plasmodium have?

A

Indirect

57
Q

What are the hosts of Plasmodium?

A

Definitive host = dipteran insect, eg. mosquito

Intermediate host = vertebrates

58
Q

What are the vectors of human malaria parasites?

A

Female anopheles mosquito

59
Q

What is the only plasmodium species that sequesters in tissues?

A

P. falciparum

60
Q

What causes cerebral malaria?

A

P. falciparum

Sequestration in cerebral venules and capillaries

61
Q

What are hypnozoites?

A

Dormant liver stages of P. ovale and P. vivax

62
Q

What kind of individuals does P. ovale infect?

A

Duffy blood group negative

63
Q

What is the only human species of malaria with a quartan life cycle?

A

P. malariae

64
Q

Which malaria is zoonotic?

A

P. knowlesi

65
Q

What are sporozoites?

A

Form released from mosquito salivary glands

Enter host bloodstream and circulate to liver

66
Q

What are merozoites?

A

Released from mature schizonts

Invade red blood cells

67
Q

What are schizonts?

A

Trophozoite inside hepatic cell as it grows in size and replicates its nucleus

Rupture and release merozoites

68
Q

What are some of the symptoms of malaria?

A
  1. Anaemia
  2. Splenomegaly
  3. Hypoglycaemia
  4. Metabolic acidosis
69
Q

How does P. falciparum modify host cells?

A

Modifies surface of infected red blood cells

Cells express parasite protein PfEMP1

Can adhere to endothelial cells due to knob-like projections

Sequestration

70
Q

What are the clinical features of cerebral malaria?

A
  1. Convulsions
  2. Impaired consciousness
  3. Unrousable coma
71
Q

What gene family encodes PfEMP1?

A

Var genes

72
Q

Why does cerebral malaria cause coma?

A
  1. Obstruction - impaired nutrient supply and waste removal
  2. Cytokines - TNFα & IL-1 stimulates inflammation
  3. Parasite toxins when RBC ruptures
73
Q

What is the most likely malarial parasite toxin?

A

Glycosylphoshatidyl inositol (GPI)

Functions as membrane anchor for merozoite surface proteins

74
Q

How do macrophages recognise GPI?

A

Toll-like receptors

75
Q

How does malaria break the integrity of the blood brain barrier?

A

PfEMP-1 binds to ICAM-1 on the endothelium of the BBB

Secondary signalling causes changes in the cytoskeleton

76
Q

How does malaria cause anaemia?

A
  1. Destruction of parasitised red blood cells during merozoite replication
  2. Destruction of uninfected red blood cells
  3. Decreased erythropoiesis
77
Q

How are red blood cells destroyed in infection?

A
  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
Q

How does malaria cause acidosis?

A

Anaemia results in failure of oxygen delivery to tissues

Increased lactate production

79
Q

What type of individuals does P. vivax infect?

A

Duffy blood group positive

80
Q

What causes sickle cell haemoglobin?

A

Val–> glu substitution in β-chain of haemoglobin

81
Q

What is the link between sickle cell anaemia and malaria?

A

Individuals heterozygous for sickle cell trait are protected against malaria

82
Q

How does sickle cell trait protect against malaria?

A
  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
Q

What is the effect of glucose-6-phosphate dehydrogenase deficiency?

A
  1. Affects parasite growth

2. Promotes efficient phagocytosis of parasitised red blood cells

84
Q

What HLA is associated with decreased malaria risk?

A

HLA-B53

Presents liver stage and sporozoite antigens to T cells

85
Q

Give five features of the structure of trematodes

A
  1. Dorsoventrally flattened body
  2. Bilateral symmetry
  3. Complex outer tegument
  4. Lack body cavity
  5. Usually hermaphrodite
86
Q

What are blood flukes?

A

Schistosomes

87
Q

What are the host of schistosomes?

A 
Intermediate = snail
Definitive = vertebrates
88
Q

How do schistosomes reproduce?

A

Separate sexes

Unique among trematodes

89
Q

Where do adult schistosomes live in the host?

A

In blood vessels round gut or bladder

90
Q

Which schistosome is zoonotic?

A

S. japonicum

91
Q

Which schistosome is only found in man?

A

S. haematobium

92
Q

What is the treatment for schistosomiasis?

A

Praziquantel

93
Q

With which species of schistosome is eosinophilia seen?

A
  1. S. haematobium

2. S. mansoni

94
Q

With which species of schistosome is IL-4 and IL-5 seen?

A
  1. S. haematobium

2. S. mansoni

95
Q

With which species of schistosome is anti-schistosome IgE seen?

A
  1. S. haematobium
  2. S. mansoni
  3. S. japonicum
96
Q

Where is the schistosome immunity gene located?

A

Near TH2 cytokine cluster on human chromosome 5

97
Q

What causes swimmer’s itch?

A

Repeat exposure to non-human schistosomes

98
Q

How does schistosomiasis cause nephrotic lesions?

A

Produces circulating antigens

Form antigen/antibody immune complexes

99
Q

What is the most obvious symptom of S. haematobium infection?

A

Haematuria

100
Q

What cancer is schistosome infection associated with?

A

Bladder squamous cell carcinoma

101
Q

What is the basic reproductive rate of macroparasites?

A

Number of next generation hermaphrodite/female worms that reach sexual maturity produced by a single worm

102
Q

How is schistosomiasis controlled?

A
  1. Chemotherapy
  2. Vector control
  3. Sanitation
  4. Education
103
Q

What is the treatment for intestinal nematodes?

A
  1. Albendazole

2. Mebendazole

104
Q

What is the only successful anti-helminth vaccine?

A

Against cattle lung worm

105
Q

What is the adaptive immune response to the liver stage of malaria?

A

Cytotoxic CD8 T cell

106
Q

What is the adaptive immune response to sporozoites, merozoites and Plasmodium proteins?

A

Antibodies

107
Q

How does malaria evade the immune system?

A
  1. Complex life cycle with antigenic diversity
  2. Different species
  3. Different strains of each species
  4. Different stages in life cycle
108
Q

How does PfEMP-1 contribute to immune evasion?

A
  1. Encoded by at least 50 var genes - antigenic diversity

2. Causes sequestration to avoid destruction of infected RBCs

109
Q

Why are women more susceptible to malaria during first pregnancy?

A

P. falciparum subpopulation expresses a PfEMP-1 that binds CSA, which is highly expressed in the placenta

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