Transmission of viruses Flashcards
This deck covers the lectures about respiratory-, fecal-oral- and sexual transmission of viruses
What are the three ways of respiratory virus transmission?
- (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
What can be said about the INF load during respiratory transmission for:
- Donor
- Interface
- Recipient
- Donor: high INF load
- Interface: stability
- Recipient: low INF load
What are the characteristics of the donor during respiratory transmission? (5)
- High viral load
- Replication in URT
- Induction of production of mucus
- Induction of clinical signs
- Host immune responses
What factors influence the interface during respiratory transmission? (5)
- Stability/survival in aerosols
- Temperature
- Relative humidity -> influences environmental survival pathogen
- Air ventilation (inside) and air movement (outside)
- UV radiation
What are the characteristics of the recipient during respiratory transmission? (4)
- Low infectious dose
- Size of virus-containing aerosols
- Tissue/cellular tropism
- Host immune responses
What kind of experiments/data generates evidence of the airborne transmission of respiratory viruses? (5)
- Outbreak reports
- Experimental infection of humans
- Animal experiments
- Data on exhaled breath
- In-vitro experiments
Describe an example of experimental infection of humans about airborne transmission of RSV
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
Why are animal experiment useful to study airborne transmission of influenza virus? (3)
- Animals are susceptible to natural infection
- Respiratory disease and lung pathology similar to humans
- Patterns of virus attachment similar to humans
What are the host differences during influenza A infection between avian- and human flu? (3)
- Target: intestinal tract vs. upper airways
- Different receptor
- Temperature: 41C vs 33C
Which questions can one ask when studying generations and collection of respiratory viruses from the air? (3)
- 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?
What are the three phases of person-to-person transmission?
- Phase 1: Generation, aerosolization and exhalation
- Phase 2: Transport via air; droplets
- Phase 3: Inhalation, deposition and infection
What are the three phases of the research agenda for respiratory transmission routes?
- Transmission routes
- Animal experiments
- In-vitro experiments
What are the parameters for respiratory emission? (3)
- Aerosols
- Droplets
- Monodisperse/heterogeneous
What are the parameters for the interface/environment? (4)
- Salinity
- Mucus
- Temperature/humidity
- Evaporation
Respiratory transmission: What are the parameters for the recipient? (4)
- (new) samplers
- Air-liquid interface cultures
- Presence of mucus
- Infectious dose
What is the definition of fecal-oral human-to-human transmission?
Transmission of a pathogen from the host (acutely ill or chronic carrier) to a susceptible human (recipient) via the fecal-oral route
Which viruses follow the fecal-oral human-to-human transmission route? (5)
- Enteric adenovirus
- Hepatitis A virus
- Norwalk virus
- Poliovirus and other enteroviruses
- Rotavirus
What makes rotavirus special?
Lower incidence, higher mortality
Which pathways of the fecal-oral route cause contamination of food? (4)
- Flies/Fomites
- Field/Floors
- Fluids
- Fingers
Which pathways of the fecal-oral route can infect the new host directly? (3)
- Field/Floors
- Fluids
- Fingers
Fecal-oral: What causes contamination of the environment? (2)
- Vomiting
- Diarrhea
What is the biggest problem in water contamination?
Heavy rainfall causing wastewater overflow
What are examples of water contamination by wastewater overflow? (3)
- Swimming water
- Irrigation water
- Growing water for oysters
What causes the increase in norovirus contamination in the fecal-oral transmission route via contaminated water-infected food?
Climate change
True or false: ‘Norovirus is an unstable virus’
False. Norovirus is really stable. Contaminated objects can cause infections up to two weeks after contamination
What are important factors for fecal-oral transmission? (3)
- Host factors
- Virus factors
- Environmental factors
Name examples of host factors important for fecal-oral transmission (3)
- Gut microbiome
- Receptor expression in intestinal tract
- Human behaviour (hygiene, agriculture, food preference)
Name examples of virus factors important for fecal-oral transmission (3)
- Shedding in stool
- Stability in the environment
- Intestinal tract niche adaptation
- Pathogenicity
What is meant with ‘pathogenicity’ of viruses causing GI-tract infections?
Ability to cause diarrhea
Name examples of environmental factors important for fecal-oral transmission (2)
- Climate
- Environmental microbiome
Is replication in the intestine necessary for shedding in the stool?
No
Which virus has liver tropism?
Hepatitis E
Which virus uses multiple routes for human-to-human transmission?
Hepatitis E
Which routes does Hepatitis E virus use for human-to-human transmission?
- Fecal-oral
- Blood-borne
What are characteristics of viruses that transmit via the fecal-oral route? (4)
- 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
What are characteristics of the harsh environment of the GI-tract? (5)
- Acidity of the stomach
- Bile salts
- Antiviral defenses (proteolytic enzymes, secretory IgA)
- Mucus and gut mobility
- M cells
What is the function of bile salts in the GI-tract?
Destruction of lipid envelops of many viruses
Most GI tract viruses don’t have an envelop to subvert the bile salts
What is the function of M cells?
Sampling of microorganisms and antigens for delivery to DCs in PP
Cell culture models are needed to study viruses to obtain information about … (4)
- General virology
- Food and environmental virology
- Clinical medicine
- Epidemiology
What is the pitfall of cell culture models to study viruses that transmit via the fecal-oral route?
They replicate poorly in cell-culture
What are the characteristics of norovirus? (6)
- RNA virus, capsid, no lipids
- Fecal shedding extremely high levels
- Low infectious dose
- Stability outside host
- Asymptomatic infections
- Fecal-oral transmission
What indicates a possible role of the microbiome in norovirus infection?
Norovirus replicates in B cells in the presence of bacteria
Name a structure of bacteria that can stabilize virus particles in the environment
LPS from gram-negative bacteria
Which animals can be used to study fecal-oral transmission? (4)
- Mini pigs
- Dogs
- Zebrafish
- Mice
Why are in vivo experimental models build?
To find better models to investigate antivirals
What is another way by which norovirus can be transmitted?
Spread through saliva
