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Human Microbial Diseases Block 2 > Pathogenesis of Acute and Persistent Infections > Flashcards

Pathogenesis of Acute and Persistent Infections Flashcards

1
Q

What is the pattern of an acute infection?

A

A single peak and a swift resolve

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2
Q

What is the pattern of a latent infection?

A

Multiple peaks with multiple resolves - bursts of acute infection

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3
Q

What is the pattern of an asymptomatic persistent infection?

A

Virus is produced all the time with no symptoms - virus production remains high with no resolve

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4
Q

What is the pattern of a pathogenic persistent infection?

A

Peaks of high viral production with resolution but with a constant low level viral production - never fully clears

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5
Q

Describe the features of an acute infection

A
  • Rapid onset of viral reproduction
  • Short but potentially severe disease course
  • High viraemia
  • Immune clearance
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6
Q

What are the benefits to the virus of a persistent infection?

A
  • Continued virus production and transmission of viral genetic material
  • With low or no fitness cost to the host, multiple infections generate genetic variability and complexity
  • Host’s health not significantly affected (short term), allowing the virus to disseminate to more hosts (same or new environment)
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7
Q

What are the benefits to the host of a persistent infection?

A
  • Persistently infected organisms are resistant to super infections with related viruses (viral accommodation)
  • Persistently infected populations can carry and transmit viruses to sensitive populations and eventually settle and/or replace them
  • Organisms persistently infected with mutualistic viruses show an increased antiviral response
  • Mutualistic viruses can help the host by supplying new genes or through epigenetic changes - can become part of our genome
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8
Q

Describe the typical acute infection course

A
  • Viral entry
  • Viral sensing and innate defenses
  • Infection establishes
  • Adaptive response is induced
  • Memory created
  • Virus clearance
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9
Q

What is the incubation period?

A
  • Before the symptoms are obvious - measurable and visible
  • At the very start of the infection
  • Corresponds to time until prodromal symptoms - symptoms before those characteristic of the disease
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10
Q

Is transmission possible in the incubation period?

A

Yes

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11
Q

What does a short incubation period suggest?

A

Replication at primary site produces symptoms

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12
Q

What does a long incubation period suggest?

A

Symptoms occur beyond primary site of infection

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13
Q

What are unapparent acute infections?

A
  • Successful infections
  • No symptoms or disease
  • Sufficient viral particles produced to spread in the population
  • We know we’ve had them due to antibodies
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14
Q

What are the types of Influenza virus?

A

A, B and C types

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15
Q

Which Influenza type is responsible for pandemics?

A

A

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16
Q

Which Influenza types cause serious illness?

A

A and B

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17
Q

Describe antigenic variation

A
  • Shift and drift

- Allows for constant emergence of new strains

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18
Q

Describe Influenza transmission

A
  • Droplets produced during coughing, sneezing and talking
  • Contact with contaminated surfaces and then touching our eyes, mouth or nose
  • Direct contact with infected individuals
19
Q

How far can droplet types spread?

A
  • Large infectious droplets = up to 1m
  • Small infectious droplets = up to 2m
  • Infectious droplet nuclei = over 50m
20
Q

Describe the pathogenesis of Influenza

A
  • Invades the mucosal surface
  • Movement of mucus usually facilitates the downwards movement of the influenza virus
  • Spreads in the respiratory tract by replicating in epithelial cells
  • Replication in the bronchioles can lead to severe damage in respiratory capacities
  • Lower the virus replicates in our respiratory tract the more acute the symptoms become
  • Surface receptors determine susceptibility to human vs avian viruses
  • Avian = alpha(2,3) sialic acid which is mainly located in the lower respiratory tract and in the cornea
  • Human = alpha(2,6) sialic acid which is mainly located in the upper respiratory tract
  • Therefore more susceptible to human respiratory viruses
21
Q

Describe what a human will experience with uncomplicated Influenza

A
  • 1-5 days incubation - depending on the dose and immune status
  • Rapid onset of headache, cough and chills
  • High fever peaking up to 40 degrees within 24 hours - malaise and myalgia
  • Days 2-3 = fever drops - gone by day 6
  • In elderly, children or immunocompromised symptoms may worsen or differ
22
Q

What dictates Influenza pandemic potential?

A
  • Avian viruses re-assorting with human viruses may lead to efficient transmission
  • Avian viruses aren’t efficiently transmitted due to lack of avian receptor in the upper respiratory tract
  • If an avian influenza virus re-assorts to exchange genetic fragments with a human virus it may create a hybrid avian human virus that will have characteristics of both
  • May be able to transmit efficiently from human to human leading to infection with a virus we have very little immunity for so symptoms could be very severe
23
Q

How are people infected with avian Influenza?

A
  • Direct contact of people working with chickens or birds
  • Contaminated surfaces - e.g. bird droppings
  • Dissemination of droplets in the air by infected birds - e.g. flapping wings, scratching, shaking their heads
24
Q

What are the complications of Influenza?

A
  • Primary viral pneumonia
  • Secondary bacterial infections
  • General muscle pain
  • Cardiac pain
  • Reye syndrome - rare - brain swelling
25
Q

How is Influenza treated?

A
  • Antiviral drugs - e.g. tamiflu (oseltamivir), relenza (zanamavir), coumarins (rimantadine)
  • Vaccine
  • Non-pharmaceutical intervention
26
Q

What does Norovirus cause?

A

Gastroenteritis

27
Q

What is the Norovirus genome?

A

Small strand RNA virus

28
Q

What family does Norovirus belong to?

A

Calciviridae

29
Q

What is the infectious dose of Norovirus?

A

Low infectious dose = 1-10 particles

30
Q

What percentage of enteritis cases does Norovirus make up in the UK?

A

40%

31
Q

How is Norovirus transmitted?

A

Food-borne - faecal-oral transmission

32
Q

How long do Norovirus symptoms last?

A

2-3 days

33
Q

How long are people with Norovirus infectious for?

A

2 weeks

34
Q

How many episodes of Norovirus will most people experience in their lifetime?

A

5

35
Q

How does Norovirus effect the villi?

A
  • Very stable virus
  • Retains infectivity passing through the stomach and GI tract
  • Blunts villi in the proximal jejunum - affects exchange process of water in the gut
36
Q

What does Norovirus do in the gut?

A
  • Needs commensal bacteria for productive infection
  • Norovirus binds carbohydrates secreted into the gut lumen by enterocytes or expressed enteric bacteria
  • Following transcytosis, Norovirus infects dendritic cells, macrophages and B cells
  • Concomitant viral-bacterial antigen presentation during Norovirus infections impacts antiviral immune responses
37
Q

What products is Norovirus carried by?

A
  • Food/water contamination
  • Shellfish
  • Berries
  • Contaminated either at the source or while being handled
38
Q

How long is the Norovirus incubation period?

A

12-48 hours

39
Q

What symptoms does Norovirus produce?

A

Rapid and sudden vomiting (children) or diarrhoea (adults) lasting 2 days

40
Q

Does infection produce long-term immunity to Norovirus?

A

No - makes vaccine difficult to develop

41
Q

What is a decision point?

A

The point where the cell recovers and clears the virus or progresses to a chronic infection

42
Q

What is clinical latency?

A

No symptoms but the virus is still replicating

43
Q

What is virological latency?

A

No replication in the period where they don’t cause symptoms

44
Q

What are the general properties of latent infections?

A
  • Low concentration or absence of viral gene products essential for production replication
  • Cells latently infected are hidden or poorly recognised by the immune system
  • Viral genome persists and can re-initiate productive infection as and when needed to spread infection to new hosts

Human Microbial Diseases Block 2 (10 decks)

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