CSIM 1.16 Viruses and Disease

Question 1

What are the three types of viral transmission?

Answer 1

Horizontal transmission
• Human to human

Vertical transmission
• Mother to baby

Zoonotic transmission
• Animal to human

Question 2

What are the main routes of horizontal transmission of viruses? (5)

Answer 2

• Respiratory
  
  • Faecal
  • Sexual
  • Mechanical
  • Urine

Question 3

Viruses transmitted through the respiratory route cause infections where?

Answer 3

Can be ‘localised’ in the respiratory tract or ‘generalised’

Question 4

Name the main localised respiratory transmitted viruses

Answer 4

Localised:
• Rhinovirus
• Influenza

Question 5

Typically how large are the most efficient infectious droplets transmitted through respiratory transmission?

Answer 5

0.3μm

Question 6

How many infectious unites are in each ml of faeces?

Answer 6

1x10^6 IU

Question 7

Which viruses can be spread through faecal-oral route?

Answer 7

• Poliovirus
  
  • Hepatitis A and E
  • Enterovirus

Question 8

Which common viruses exhibit vertical transmission?

Answer 8

• HIV
  
  • Rubella (congenital rubella syndrome)
  • Parvovirus B19 (hydrops)

Question 9

Which group of viruses is used to describe viruses transmitted by arthropod vectors (ZOONOSES)?

Give examples

Answer 9

Arboviruses:
• Dengue fever
• Yellow fever
• Japanese encephalitis

Question 10

How is rabies transmitted?

Answer 10

Zoonotically

Question 11

Can zoonotically transmitted diseases be spread human-to-human?

Answer 11

No, usually humans are a ‘dead-end’ host and infected accidentally

Question 12

Describe how yellow fever reaches humans

Answer 12

Mosquito bites infected monkey or human

The same mosquito bites another human

Question 13

Define:

1) Pathogenicity
2) Pathogenicity factors
3) Virulence

Answer 13

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)

Question 14

Define generalised and localised infection?

Answer 14

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

Question 15

Name the main generalised viruses

Answer 15

• Polio
  
  • Measles
  • Hepatitis
  • Rabies

Question 16

Name a localised viral infection of the GI epithelium

Answer 16

Norovirus

Question 17

Describe the pathogenic pathways of local infections

Answer 17

• Entry (into host)
  
  • Replication
  • Dissemination

All local and efficient, dissemination can occur through sneezing (IMG 41)

Question 18

Describe the pathogenicity of generalised infections

Answer 18

• 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

Question 19

What is primary and secondary viraemia?

Answer 19

Primary viraemia:
• First entry of virus into the blood

Secondary viraemia:
• Further entry to bloodstream due to amplification

Question 20

Define the:

1) Incubation period
2) Generation time
3) Infectious period

Answer 20

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

Question 21

What are the four categories of incubation period and describe the common characteristics of viruses with each of these ranges of incubation period?

Answer 21

Short (

Question 22

What is R0?

Answer 22

The reproduction number:

The number of subsequent infections in a susceptible population caused by a viral illness in one individual during its invective period

Question 23

What are the possible disease patterns for viral diseases?

Answer 23

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)

Question 24

Give common examples of latent infections

Answer 24

• Shingles in those who had chickenpox

* Coldsores in those who have HSV-1