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Microbiology > 7- Mechanism of viral infection and pathogenesis > Flashcards

7- Mechanism of viral infection and pathogenesis Flashcards

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Biology 101 flashcards
1
Q

Why do most viruses not infect humans?

A

➝ they are adapted to non-human hosts
➝ they are excluded by surface barriers
➝innate immunity prevents them establishing
➝ our adaptive immune response has seen something similar

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2
Q

What are 10 common viruses in humans and 2 eradicated ones?

A 
➝ influenza
➝ cold
➝ measles
➝ mumps
➝ chicken pox/shingles
➝ glandular fever
➝ hepatitis
➝ papilloma
➝ AIDS
➝ Kaposi's sarcoma
➝smallpox (eradicated)
➝ poliomyelitis (eradicated)
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3
Q

What are the 9 sites of microbe entry?

A 
➝ conjunctive
➝ respiratory tract
➝ alimentary tract
➝ urogenital tract
➝ anus
➝ skin
➝ capillary
➝ scratch, injury
➝ arthropod vector
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4
Q

What is acute infection?

A

➝ When there is a large viral load that either gets cleared or death occurs

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5
Q

What are latent reactivating infections?

A

➝ Chronic infection
➝ Bursts of viral replication and disease with periods of latency in between
➝ Life-long infection, controlled by immunity

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6
Q

What are the 8 herpes viruses?

A 
➝ HHV-1
➝ HHV-2
➝ HHV-3 (varicella zoster virus)
➝ HHV-4- Epstein-Barr virus
➝ HHV-5 - Cytomegalovirus
➝ HH-V6
➝ HHV-7
➝ HHV-8
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7
Q

Give 4 examples of acute infections

A

➝ Common cold
➝ Measles
➝ Ebola
➝ Small pox

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8
Q

Which viruses cause latent/ reactivating infections?

A

➝ Human Herpes Viruses

➝ 8

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9
Q

What does HHV-1 cause?

A

➝ Primary Gingivostomatitis
➝ Cold sores
➝ Encephalitis when immunosuppressed (rare)

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10
Q

What does HHV-3 cause?

A

➝ chickenpox

➝ shingles

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11
Q

Describe how HHV reactivate?

A

➝ The viruses travel up sensory neurons in dorsal root ganglions, immunoprivileged site
➝ establish a latent infection
➝ virus switches off its gene expression and the immune system keeps it under control
➝The infections are in dorsal root ganglia and sensory neurons
➝When there is an insult to immune system such as X-ray radiation, immunosuppression, then the virus move out of the latent state, travel back down the neuron
➝ cause much more specific and localised lesions where the tissue is innervated by an infected neuron.

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12
Q

What are persistent infections?

A

➝ chronic infection
➝ virus continually present in body
➝ initial round of viremia, low virus load
➝viral levels constantly controlled by active host immunity
➝ changes in antigenic surfaces of virus causes eruptions
➝ mortality if immune system cannot control virus

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13
Q

Give 4 examples of of persistent infections

A

➝ HIV- retrovirus
➝ HCV- flavivirus
➝ Measles
➝ Congenital Rubella

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14
Q

Why are measles persistent?

A

➝ cause acute infection
➝ but virus shed for several weeks after acute infection
➝ rare encephalitis cases years after infection

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15
Q

What cells does HIV infect?

A

➝ CD4

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16
Q

What cells does HCV infect?

A

➝ Hepatocytes and damages the liver

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17
Q

What happens if a baby is infected with congenital rubella in utero?

A

➝ virus level stays up
➝ inability to create adaptive immune response
➝ virus is seen as self
➝ the baby is born immunotolerant and the virus continues to replicate and cause damage in neonatal tissues

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18
Q

What constitutes a successful virus?

A

➝ one that replicates well enough to spread to the next host

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19
Q

Describe viral infections.

A

➝ apathogenic or associated with relatively mild symptoms

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20
Q

What does pathogenesis result from?

A

➝ cell and tissue damage caused by viral infection

On most occasions the damage is limited by the host’s immune system

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21
Q

What is immunopathology?

A

➝ relative limited damage caused by the virus is made worse or even caused by the host’s immune system

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22
Q

What % of poliovirus infections are asymptomatic?

A

➝ 90%

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23
Q

Name 2 inapparent (asymptomatic) infections

A

➝ poliovirus

➝ parainfluenza virus 5

24
Q

What flu often give rise to?

A

➝ very mild respiratory disease

25
Q

State 2 terms that describe viruses that cause inapparent infections.

A

➝ non-cytopathic

➝ host-adapted

26
Q

What are three examples of viruses that cause cytopathic damage?

A

➝ Ebola virus
➝ Influenza A
➝ RSV

27
Q

How does Ebola cause cytopathic damage?

A

➝ it targets the vascular endothelial cells

➝ binds to receptors that are only expressed on vascular endothelium

28
Q

How does influenza A cause cytopathic damage?

A

➝ destroys lung epithelia

29
Q

How does RSV cause cytopathic damage?

A

➝ Induces syncytia in lung epithelia which cause the cells to fuse together

30
Q

What % of people get chronic liver inflammation in hepatitis C?

A

➝ 80%

31
Q

What is hepatitis associated with?

A

➝ extensive liver infiltration of leukocytes

32
Q

What are the stages of hepatitis C?

A

➝ Acute infection
➝ Chronic inflammation
➝ Fibrosis
➝ Cirrhosis or Cancer

33
Q

What is Hepatitis C persistence associated with?

A

➝ generation of HCV variants that are not recognised by CD8+ cells

34
Q

What is viral clearance and disease in hepatitis C associated with?

A

➝ generation and infiltration of CD8+ cells which attack infected cells and destroy them

35
Q

What is chronic hepatitis?

A

➝ disease of severe liver damage and loss of hepatocytes

➝ caused by persistent HCV infection

36
Q

What is the most common mosquito-borne infection in the world?

A

➝ Dengue virus infection

37
Q

What is the fatality rate from severe dengue?

A

➝ 1-5%

38
Q

Why are 2.5 billion people at risk of dengue?

A

➝ they live in an endemic area

39
Q

How many serotypes of dengue are there?

A

➝ 4, all of which have the same clinical manifestations

40
Q

What are the symptoms of primary infection with dengue virus?

A 
➝ Mild fever 
➝ Skin rash 
➝ Headache
➝ Bone & muscle pain
➝ Nausea
➝ vomiting
41
Q

What are the symptoms of secondary heterotypic infection with dengue virus?

A 
➝ Acute fever 
➝ Severe abdominal pain
➝ Headache 
➝ Plasma leakage 
➝ Intravascular volume depletion 
➝ Coagulation dysfunction
42
Q

What can happen in severe dengue?

A

➝ Haemorrhage

➝ Dengue shock syndrome

43
Q

What people are at greatest risk for contracting the most severe serotype of dengue?

A

➝ people with previous infections with a different serotype

44
Q

What does ADE stand for?

A

➝ Antibody dependent enhancement

45
Q

Describe the antibodies formed in response to a dengue infection

A

➝ they are not cross-protective against other subtypes of the virus.
➝ may result in more severe disease due to ADE

46
Q

What is ADE and how can this lead to death?

A

➝ The antibodies to the other serotypes coat the new virus
➝ they are non-neutralising but they are not as good because it is not specific to the new strain so it creates a target
➝ They form immune complexes which get internalised into mononuclear phagocytes through their Fc gamma receptors into macrophages which is where dengue replicates
➝ fixation of complement by circulating immune complexes results in release of products of the complement cascade leading to sudden and increased vascular permeability, shock and death

47
Q

How can RSV infections eventually lead to allergy/asthma?

A

➝ RSV infections in early life show unbalanced Th1/Th2 responses
➝ This depresses inflammatory cytokine production, CD8+ responses and IgG production, meaning clearance is slow and development of memory is poor
➝ This enhances IgE production, leading to allergy/asthma on re-exposure

48
Q

What does disease severity depend on?

A

➝ on what you have been infected by before

➝ adaptive immune system is imp for controlling severity of infections

49
Q

In what age groups is influenza a serious problem?

A

➝ old or children with asthma

50
Q

What are the 5 pathologies of influenza?

A 
➝ mild URTI to severe LRTI
➝ lower respiratory tract infection (LRTI) causing damage to lung epithelia and viral pneumonia, often secondary pneumonia
➝ fever, often prolonged
➝ neurological (headache, malaise)
➝ myalgia
51
Q

Why is the flu not 100% effective?

A

➝ antigenic drift- antigens on surface change

52
Q

How does infection generate a powerful long-live immunity?

A

➝ You make neutralising antibodies against your last infection
➝Sometimes these are OK against your next infection, sometimes they are not
➝ You make a T cell response against your last infection
➝ This should be effective against your next infection

53
Q

What can we get every 20-40 years?

A

➝ get a strain of influenza virus that causes much more morbidity and mortality
➝ Sometimes the virus can have enhanced pathogenicity but
the virus has changed its surface proteins (H and N) and there is no widespread immunity to it
➝ antigenic shift- vaccine do not help if you don’t know what is coming

54
Q

What is the most common strain of influenza?

A

➝ H3N2

55
Q

What did the severity of 1918 ‘Spanish’ flu show?

A

➝ extreme age distribution

56
Q

What do different strains produce?

A

➝ a huge range of outcomes

➝ sometimes you just get unlucky

57
Q

Overall, what 3 things does the outcome of an infection depend on?

A

➝ what you are infected by
➝ whether you have seen it or anything like it before
➝ state of your immune system

Microbiology (11 decks)

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