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I&I WC1 > Transmission of infectious disease > Flashcards

Transmission of infectious disease Flashcards

1
Q

Which three groups of factors are important in pathogen transmission?

A
  1. Donor factors
  2. Host & pathogen interface interactions
  3. Recipient factors
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2
Q

What are the modes of respiratory virus transmission? (3)

A
  1. Indirect contact -> transmission via fomites
  2. Large droplets (>5 µm) which can land on mucosal surfaces of people in close proximity
  3. Aerosols (<5 µm), which are inhaled and deposited in respiratory tracts
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3
Q

What is the major difference between large droplets and aerosols?

A

The time they can be airborne, and as a result of that: the distance they can travel

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4
Q

Which are the forces acting on particles in an aerosol? (3)

A
  1. Gravity -> becomes smaller as particle becomes smaller
  2. Diffusion forces
  3. Drag forces
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5
Q

Particles in an aerosol originating from the URT are [larger/smaller] than particles originating from the LRT

A

Larger (so: the deeper the particle is formed, the smaller it is)

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6
Q

The [larger/smaller] a droplet is, the deeper it travels into the respiratory tract of the person inhaling them

A

Smaller

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7
Q

Which donor factors are needed for efficient respiratory transmission? (5)

A

High infectious load ->
1. High viral load
2. Replication in URT
3. Induction of mucous production
4. Induction of clinical signs such as coughing or sneezing
5. Host immune responses

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8
Q

Which factors influence the stability of particles/respiratory viruses while airborne? (5)

A
  1. Enveloped/non-enveloped virus
  2. Temperature
  3. Relative humidity
  4. Ventilation/air movement
  5. UV radiation
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9
Q

Which recipient factors influence respiratory virus transmission? (4)

A
  1. Infectious dose received
  2. Size of virus-containing aerosols
  3. Tissue/cellular tropism
  4. Host immune responses
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10
Q

Which animals are commonly used to study respiratory transmission of influenza A?

A

Ferrets

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11
Q

What makes ferrets a good model system for respiratory transmission of influenza A? (4)

A
  1. Susceptible to natural infection
  2. Respiratory disease & lung pathology similar to humans
  3. Patterns of virus attachment similar to humans
  4. Useful for airborne transmission
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12
Q

What are the differences between avian flu and human flu when it comes to:
1. Organ targeted
2. Receptor
3. Receptor location in humans
4. Temperature

A
  1. Avian flu targets the intestinal tract, while human flu targets the upper airways
  2. Neu5Ac-α2,3-Gal for avian flu, Neu5Ac-α2,6-Gal for human flu
  3. Neu5Ac-α2,3-Gal is located in the LRT in humans, while Neu5Ac-α2,6-Gal is located in the URT
  4. Avian flu is optimal at 41 °C, while human flu is optimal at 33 °C
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13
Q

Why does avian flu cause lower respiratory symptoms in humans?

A

Its entry receptor (Neu5Ac-α2,3-Gal) is located in the LRT of humans

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14
Q

Why does human flu cause upper respiratory infection in humans?

A

Its entry receptor (Neu5Ac-α2,6,Gal) is located in the URT of humans

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15
Q

Why is it beneficial to human flu that its optimal temperature is 33 °C?

A

This is the approximate temperature of inhaled air

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16
Q

Which sources/experiments can be used to obtain information about the shedding of respiratory viruses? (5)

A
  1. Outbreak reports
  2. Experimental infection of humans
  3. Animal models
  4. Data on exhaled breath
  5. In vitro experiments such as artificial aerosolization & collection
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17
Q

What are three common ways of faecal-oral transmission?

A
  1. Contamination of the environment
  2. Contamination of fomites
  3. ‘Fingers to food’
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18
Q

Under which conditions do large outbreaks of faecal-oral transmitted pathogens often occur?

A

When a pathogen gets incorporated during processing of food

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19
Q

What is the difference to ‘small’ food handlers and large food producers when it comes to faecal-oral transmission?

A

Small food handlers often cause local, endemic outbreaks, whereas large food producers ship their foods (and possible pathogens) worldwide

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20
Q

What are donor factors that can influence faecal-oral transmission? (5)

A
  1. Shedding in stool
  2. Pathogen stability
  3. Intestinal niche adaptation of pathogen
  4. Pathogenicity (=ability to cause diarrhoea) of pathogen
  5. Gut microbiome of host
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21
Q

The gut microbiome of the host has most effect on feacal-oral transmission of [viruses/bacteria]

A

Bacteria

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22
Q

What are host-pathogen interface interactions that influence faecal-oral transmission? (4)

A
  1. Environmental microbiome
  2. Environment (climate, UV-radiation)
  3. Stability of pathogen in the environment
  4. Human behaviour
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23
Q

What kind of climate is generally more stable for transmission of pathogens? Why?

A

Cool climate -> pathogens are generally more stable at lower temperatures

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24
Q

Which human behavioural factors are important for host-pathogen interface interactions? (3)

A
  1. Hygiene
  2. Agriculture
  3. Food preference
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25
Q

What are recipient factors that are important for faecal-oral transmission? (4)

A
  1. Microbiome of recipient
  2. Receptor expression in intestinal tract
  3. Stability of pathogen in new host
  4. Intestinal tract niche adaptation of pathogen
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26
Q

What are common characteristics of viruses that transmit via the faecal-oral route? (4)

A
  1. Viruses shed via the stool
  2. Clinical symptoms increase likelihood of faecal-oral transmission (vomiting, diarrhoea)
  3. Viruses have to be stable in the environment
  4. Viruses have to adapt to (harsh) conditions in the intestinal tract
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27
Q

True or false: for viruses to be shed via the stool, they need to be produced in the intestinal tract

A

False; viruses that replicate elsewhere can also move to the intestine after replication and end up in the stool

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28
Q

Which factors in the mouth make it hard for pathogens to survive or attach there? (3)

A
  1. Flow of liquids, preventing attachment
  2. Proteins in saliva (lysozyme, etc.)
  3. Presence of normal flora
29
Q

What is the effect of stomach acid on pathogens?

A

Inactivation/killing of acid liable bacteria/viruses

30
Q

Which factors in the duodenum can kill viruses?

A

Bile salts -> can destroy lipid envelopes of many viruses

31
Q

Why is the presence of bile salts sometimes beneficial for pathogens?

A

Some gastrointestinal viruses require presence of bile salts to get internalized in intestinal cells

32
Q

Which factors in the intestine are important to prevent infection? (6)

A
  1. Peristalsis -> prevents microorganisms
  2. Flow of liquids
  3. Shedding of epithelium, hindering establishment of pathogens
  4. Mucus -> hinders binding of microorganisms
  5. Antiviral defences such as proteolytic enzymes & IgA
  6. M-cells sample intestines and activate adaptive immunity if necessary
33
Q

Which factors in the colon prevent infection? (3)

A
  1. Normal flora
  2. Peristalsis
  3. Shedding of epithelium
34
Q

Why is the majority of gastro-intestinal viruses ‘naked’?

A

These viruses lack a lipid envelope, causing them to be more stable in the harsh environment of the gastrointestinal tract

35
Q

What model systems are available to study faecal-oral transmission? (3)

A
  1. Cell culture models
  2. Animal models
  3. Mechanical models
36
Q

Why are cel culture systems for enteric viruses difficult to find?

A

Many viruses that replicate in the intestinal tract don’t replicate in cell culture

37
Q

What are the structural characteristics of norovirus?

A

RNA capsid virus, no envelope

38
Q

The infectious dose required to establish a norovirus infection is [high/low]

A

Low

39
Q

Which factors make norovirus a very infectious gastro-intestinal virus? (4)

A
  1. Faecal shedding in extremely high levels
  2. Low infectious dose
  3. Stable outside host
  4. Can cause asymptomatic infections
40
Q

Why is norovirus unable to infect B-cells on its own, but is able to do so in the presence of bacteria?

A

LPS on bacteria can stabilize virus particles, allowing them to cause infection

41
Q

What are donor factors that influence the transmission of HIV? (3)

A
  1. High viral load
  2. Virus tropism
  3. Transmission fitness of virus
42
Q

Which factors determine the viral load in HIV-infected individuals? (2)

A
  1. Stage of infection
  2. Use of PrEP/PEP/cART
43
Q

Which sexual intercourse factors influence HIV transmission?

A
  1. Condom use
  2. Type of sexual intercourse
44
Q

Which recipient factors influence the transmission of HIV? (5)

A
  1. Use of PrEP/PEP
  2. Virus tropism
  3. Presence of STDs -> increase chance
  4. Biologial sex -> females more at risk
  5. Presence of foreskin
45
Q

Which three stages does HIV-infection have?

A
  1. Acute infection
  2. Chronic infection
  3. AIDS
46
Q

How long does the acute stage of HIV-infection last?

A

10-16 weeks

47
Q

What symptoms are characteristic of acute HIV infection? (5)

A

Flu-like symptoms, such as:
1. Headache
2. Fever
3. Lymphadenopathy
4. Malaise
5. Rash

48
Q

Why can’t HIV be diagnosed based on symptoms? (2)

A
  1. Only ~50% of infected individuals experience symptoms
  2. Symptoms are aspecific
49
Q

How long does the chronic stage of HIV-infection last (on average) before AIDS occurs?

A

~8 years

50
Q

What symptoms can be present during acute HIV-infection?

A

Fatigue & lymphadenopathy (present in minority of patients during minority of time)

51
Q

What is AIDS?

A

Occurence of opportunistic infections due to increasing immune system dysfunction

52
Q

Which symptoms may occur during AIDS, in addition to infections? (2)

A
  1. Weight loss/wasting
  2. Dementia
53
Q

True or false: individuals with AIDS can have their life expectancy fully restored when they receive treatment

A

False; when a person reaches AIDS, their life expectancy is reduced, even if CD4-count is restored using treatment

54
Q

Which stage of HIV-infection is key for prevention?

A

Acute stage -> low symptoms & high viral load = high transmission

55
Q

Which type of sexual activity has lowest chances of transmission of HIV?

A

Heterosexual transmission

56
Q

Why is the chance of transmission of HIV higher in MSM?

A

Anal sexual intercourse leads to small abrasions, allowing for easy infection

57
Q

Which event has the highest transmission chance for HIV?

A

Blood transfusion

58
Q

HIV requires a [high/low] infectious dose to establish infection

A

Low -> max. 2 virus copies establish an infection

59
Q

How can it be established that max. 2 virus copies establish HIV infection?

A

Low genetic variation of viruses in a single patients points to a (very) low number of original viruses

60
Q

How can the low risk per sexual act of HIV be explained?

A

Low amount of virus particles causing infection can explain the low chance

61
Q

What is a bottleneck event? Why is it relevant in the context of the transmission of HIV?

A

A reduction of genetic diversity in a population -> because only 1/2 viruses establish infection in a new host, genetic diversity in the new host is drastically reduced when compared to the original host

62
Q

What is a quasi-species?

A

Cloud of genetically different viruses

63
Q

What is Fiebig staging?

A

Clinical classification of acute HIV infection based on an ordered appearance of particular events

64
Q

Which two factors are the main reasons for the high infectiousness of acute HIV?

A
  1. High viral load
  2. Viruses in the acute stage infected somebody recently -> still have high transmission fitness
65
Q

Why do viruses in chronic HIV lose (part of) their transmission fitness?

A

Adaption to host causes lower efficiency in infecting new individuals

66
Q

How does HIV disseminate after infection? (2)

A
  1. Local stage -> exponential growth
  2. Dissemination & establishment in lymhoid tissues
67
Q

Why is the local stage of HIV a window of opportunity?

A

The virus stays local for 2-5 days and can still be exterminated using PEP

68
Q

How quickly after infection should PEP be started?

A

Within 72 hours of infection

69
Q

Why is PEP effective? (2)

A
  1. Small founder population due to low number of HIV-copies establishing infection
  2. Local infection stage that can be countered

I&I WC1 (20 decks)

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