CSIM 1.16 Viruses and Disease Flashcards
What are the three types of viral transmission?
Horizontal transmission
• Human to human
Vertical transmission
• Mother to baby
Zoonotic transmission
• Animal to human
What are the main routes of horizontal transmission of viruses? (5)
- Respiratory
- Faecal
- Sexual
- Mechanical
- Urine
Viruses transmitted through the respiratory route cause infections where?
Can be ‘localised’ in the respiratory tract or ‘generalised’
Name the main localised respiratory transmitted viruses
Localised:
• Rhinovirus
• Influenza
Typically how large are the most efficient infectious droplets transmitted through respiratory transmission?
0.3μm
How many infectious unites are in each ml of faeces?
1x10^6 IU
Which viruses can be spread through faecal-oral route?
- Poliovirus
- Hepatitis A and E
- Enterovirus
Which common viruses exhibit vertical transmission?
- HIV
- Rubella (congenital rubella syndrome)
- Parvovirus B19 (hydrops)
Which group of viruses is used to describe viruses transmitted by arthropod vectors (ZOONOSES)?
Give examples
Arboviruses:
• Dengue fever
• Yellow fever
• Japanese encephalitis
How is rabies transmitted?
Zoonotically
Can zoonotically transmitted diseases be spread human-to-human?
No, usually humans are a ‘dead-end’ host and infected accidentally
Describe how yellow fever reaches humans
Mosquito bites infected monkey or human
The same mosquito bites another human
Define:
1) Pathogenicity
2) Pathogenicity factors
3) Virulence
1) The severity of disease caused by different viruses
2) The characteristics that disease-causing viruses possess in their pathogenesis
3) The severity of disease caused by different strains of the same virus (e.g. how many virions it requires to kill a mouse)
Define generalised and localised infection?
Localised:
• Infections at tissues at or contiguous with the site of entry
Generalised
• Infections that spread to target organs or tissues remote from the site of entry
Name the main generalised viruses
- Polio
- Measles
- Hepatitis
- Rabies
Name a localised viral infection of the GI epithelium
Norovirus
Describe the pathogenic pathways of local infections
- Entry (into host)
- Replication
- Dissemination
All local and efficient, dissemination can occur through sneezing (IMG 41)
Describe the pathogenicity of generalised infections
- Entry
- Enters regional lymphatics, to local lymph node and replicated
- Primary viraemia from lymphatics
- Further replication in other tissues (spleen, liver and bone marrow)
- Secondary viraemia due to large amount of virus that spills out of above tissues
- Distribution to target organs
- Distribution to respiratory mucosa for dissemination
What is primary and secondary viraemia?
Primary viraemia:
• First entry of virus into the blood
Secondary viraemia:
• Further entry to bloodstream due to amplification
Define the:
1) Incubation period
2) Generation time
3) Infectious period
1) The time period between viral exposure on onset of illness
2) Time period between viral exposure and onset of infectiousness
3) Onset to end of infectiousness
IMG 43
What are the four categories of incubation period and describe the common characteristics of viruses with each of these ranges of incubation period?
Short (
What is R0?
The reproduction number:
The number of subsequent infections in a susceptible population caused by a viral illness in one individual during its invective period
What are the possible disease patterns for viral diseases?
Acute infections
• Influenza, rhinovirus, rabies
Subclinical infections
• Poliovirus
Chronic persistent
• Acute or subclinical infections that are not terminated by an immune response
• Hepatitis B
Latent infections
• Acute infection followed by a persistent latent infection where virus becomes dormant within the host cell
Slowly progressive diseases
• Virus replicates at normal rates but takes many years to manifest
• Can be infectious (HIV-1, can spread to others) or non-infectious (SSPE, cannot spread to others)
Give common examples of latent infections
- Shingles in those who had chickenpox
* Coldsores in those who have HSV-1
