Transmission of viruses

Question 1

What are the three ways of respiratory virus transmission?

Answer 1

• (In)direct contact through inoculation of fomites
• Large droplets land on mucosa of person in close proximity
• Aerosols are inhaled and deposited in respiratory tract

Question 2

What can be said about the INF load during respiratory transmission for:
- Donor
- Interface
- Recipient

Answer 2

• Donor: high INF load
• Interface: stability
• Recipient: low INF load

Question 3

What are the characteristics of the donor during respiratory transmission? (5)

Answer 3

• High viral load
• Replication in URT
• Induction of production of mucus
• Induction of clinical signs
• Host immune responses

Question 4

What factors influence the interface during respiratory transmission? (5)

Answer 4

• Stability/survival in aerosols
• Temperature
• Relative humidity -> influences environmental survival pathogen
• Air ventilation (inside) and air movement (outside)
• UV radiation

Question 5

What are the characteristics of the recipient during respiratory transmission? (4)

Answer 5

• Low infectious dose
• Size of virus-containing aerosols
• Tissue/cellular tropism
• Host immune responses

Question 6

What kind of experiments/data generates evidence of the airborne transmission of respiratory viruses? (5)

Answer 6

• Outbreak reports
• Experimental infection of humans
• Animal experiments
• Data on exhaled breath
• In-vitro experiments

Question 7

Describe an example of experimental infection of humans about airborne transmission of RSV

Answer 7

Young adults were divided into three groups to measure airborne transmission
- Cuddlers: caring for the baby in the usual manner
- Touchers: volunteers touched the contaminated surfaces
- Sitters: Exposed by sitting at a distance of more than 6 ft

Question 8

Why are animal experiment useful to study airborne transmission of influenza virus? (3)

Answer 8

• Animals are susceptible to natural infection
• Respiratory disease and lung pathology similar to humans
• Patterns of virus attachment similar to humans

Question 9

What are the host differences during influenza A infection between avian- and human flu? (3)

Answer 9

• Target: intestinal tract vs. upper airways
• Different receptor
• Temperature: 41C vs 33C

Question 10

Which questions can one ask when studying generations and collection of respiratory viruses from the air? (3)

Answer 10

• Which respiratory viruses can be found in the air? For how long? Are they still infectious?
• Which particles contain virus? Large droplets or small aerosols?
• What is the viral load in the air?

Question 11

What are the three phases of person-to-person transmission?

Answer 11

• Phase 1: Generation, aerosolization and exhalation
• Phase 2: Transport via air; droplets
• Phase 3: Inhalation, deposition and infection

Question 12

What are the three phases of the research agenda for respiratory transmission routes?

Answer 12

• Transmission routes
• Animal experiments
• In-vitro experiments

Question 13

What are the parameters for respiratory emission? (3)

Answer 13

• Aerosols
• Droplets
• Monodisperse/heterogeneous

Question 14

What are the parameters for the interface/environment? (4)

Answer 14

• Salinity
• Mucus
• Temperature/humidity
• Evaporation

Question 15

Respiratory transmission: What are the parameters for the recipient? (4)

Answer 15

• (new) samplers
• Air-liquid interface cultures
• Presence of mucus
• Infectious dose

Question 16

What is the definition of fecal-oral human-to-human transmission?

Answer 16

Transmission of a pathogen from the host (acutely ill or chronic carrier) to a susceptible human (recipient) via the fecal-oral route

Question 17

Which viruses follow the fecal-oral human-to-human transmission route? (5)

Answer 17

• Enteric adenovirus
• Hepatitis A virus
• Norwalk virus
• Poliovirus and other enteroviruses
• Rotavirus

Question 18

What makes rotavirus special?

Answer 18

Lower incidence, higher mortality

Question 19

Which pathways of the fecal-oral route cause contamination of food? (4)

Answer 19

• Flies/Fomites
• Field/Floors
• Fluids
• Fingers

Question 20

Which pathways of the fecal-oral route can infect the new host directly? (3)

Answer 20

• Field/Floors
• Fluids
• Fingers

Question 21

Fecal-oral: What causes contamination of the environment? (2)

Answer 21

• Vomiting
• Diarrhea

Question 22

What is the biggest problem in water contamination?

Answer 22

Heavy rainfall causing wastewater overflow

Question 23

What are examples of water contamination by wastewater overflow? (3)

Answer 23

• Swimming water
• Irrigation water
• Growing water for oysters

Question 24

What causes the increase in norovirus contamination in the fecal-oral transmission route via contaminated water-infected food?

Answer 24

Climate change

Question 25

True or false: 'Norovirus is an unstable virus'

Answer 25

False. Norovirus is really stable. Contaminated objects can cause infections up to two weeks after contamination

Question 26

What are important factors for fecal-oral transmission? (3)

Answer 26

- Host factors - Virus factors - Environmental factors

Question 27

Name examples of host factors important for fecal-oral transmission (3)

Answer 27

- Gut microbiome - Receptor expression in intestinal tract - Human behaviour (hygiene, agriculture, food preference)

Question 28

Name examples of virus factors important for fecal-oral transmission (3)

Answer 28

- Shedding in stool - Stability in the environment - Intestinal tract niche adaptation - Pathogenicity

Question 29

What is meant with 'pathogenicity' of viruses causing GI-tract infections?

Answer 29

Ability to cause diarrhea

Question 30

Name examples of environmental factors important for fecal-oral transmission (2)

Answer 30

- Climate - Environmental microbiome

Question 31

Is replication in the intestine necessary for shedding in the stool?

Answer 31

No

Question 32

Which virus has liver tropism?

Answer 32

Hepatitis E

Question 33

Which virus uses multiple routes for human-to-human transmission?

Answer 33

Hepatitis E

Question 34

Which routes does Hepatitis E virus use for human-to-human transmission?

Answer 34

- Fecal-oral - Blood-borne

Question 35

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

Answer 35

- Viruses have to shed via the stool - Clinical symptoms can increase the likelihood of fecal-oral transmission - Stability of viruses in the environment - Viruses have to adapt to the (harsh) conditions of the intestinal tract

Question 36

What are characteristics of the harsh environment of the GI-tract? (5)

Answer 36

- Acidity of the stomach - Bile salts - Antiviral defenses (proteolytic enzymes, secretory IgA) - Mucus and gut mobility - M cells

Question 37

What is the function of bile salts in the GI-tract?

Answer 37

Destruction of lipid envelops of many viruses | Most GI tract viruses don't have an envelop to subvert the bile salts

Question 38

What is the function of M cells?

Answer 38

Sampling of microorganisms and antigens for delivery to DCs in PP

Question 39

Cell culture models are needed to study viruses to obtain information about … (4)

Answer 39

- General virology - Food and environmental virology - Clinical medicine - Epidemiology

Question 40

What is the pitfall of cell culture models to study viruses that transmit via the fecal-oral route?

Answer 40

They replicate poorly in cell-culture

Question 41

What are the characteristics of norovirus? (6)

Answer 41

- RNA virus, capsid, no lipids - Fecal shedding extremely high levels - Low infectious dose - Stability outside host - Asymptomatic infections - Fecal-oral transmission

Question 42

What indicates a possible role of the microbiome in norovirus infection?

Answer 42

Norovirus replicates in B cells in the presence of bacteria

Question 43

Name a structure of bacteria that can stabilize virus particles in the environment

Answer 43

LPS from gram-negative bacteria

Question 44

Which animals can be used to study fecal-oral transmission? (4)

Answer 44

- Mini pigs - Dogs - Zebrafish - Mice

Question 45

Why are in vivo experimental models build?

Answer 45

To find better models to investigate antivirals

Question 46

What is another way by which norovirus can be transmitted?

Answer 46

Spread through saliva