Viral Pathogenesis

Question 1

Why can’t viruses infect the outer layer of skin?

Answer 1

Because skin’s outer layer is keratinous so the cells are essentially dead - viruses can’t infect dead cells

Question 2

Which viruses infect the respiratory system and remain localised?

Answer 2

rhinovirus, respiratory syncitial virus, influenza virus

Question 3

Which viruses infect the respiratory system but spread systemically?

Answer 3

mumps, measels, rubella, varicella-zoster

Question 4

What are the most common viral causes of upper respiratory tract infections?

Answer 4

rhinovirus, coronavirus, adenovirus

Question 5

What is the most common viral cause of pharyngitis?

Answer 5

adenovirus

Question 6

What is the most common viral cause of croup?

Answer 6

parainfluenza

Question 7

What is the most common viral cause of bronchiolitis?

Answer 7

respiratory syncitial virus, parainfluenza 3

Question 8

What is the most common viral cause of pneumonia?

Answer 8

respiratory syncitial virus, parainfluenza 3, influenza virus, adenovirus

Question 9

What is the cytopathic effect of respiratory syncitial virus?

Answer 9

Giant cells

Question 10

What are koplick spots?

Answer 10

Spots on the inside of the mouth in measles - where lymphocytes come in to fight the virus

Question 11

How does the measles virus get from the respiratory tract to a systemic infection?

Answer 11

By infecting local macrophages, lymphocytes and dendritic cells which then drain to the lymph nodes where they amplify and then enter circulation

Question 12

How is measles transmitted to another person?

Answer 12

Because it returns to the epithelium of the lungs and mouth and is then breathed out (not coughed out)

Question 13

Why does measles cause transient immunosuppresion?

Answer 13

Because it replicates in cells of the immune system

Question 14

What kind of viruses enter via the alimentary tract?

Answer 14

Icosahedral viruses without an envelope and possibly multiple capsids - to have the best defence against the many barriers to infection

Question 15

What virus stays local in the alimentary tract?

Answer 15

rotavirus

Question 16

What viruses gain entry via the alimentary tract and then spread systemically?

Answer 16

poliovirus, hepatitis A virus

Question 17

How do viruses gain entry to the alimentary tract if they don’t have receptors for the epithelial cells?

Answer 17

By a breach of the epithelial surface e.g. abrasions in rectum can lead to HIV and hepatitis B infections

Question 18

How does rotavirus cause diarrhoea?

Answer 18

By infecting and destroying enterocytes which prevents them from absorbing water - and also by encoding for a protein NSP4 which acts like a cholera toxin to increase fluid loss

Question 19

What happens when infected with an enterovirus?

Answer 19

The virus enters via aerosol or ingestion, then replicates in the oropharynx and is then ingested and replicates in the peyer’s patches, then spread to the circulation to cause primeria viremia and then spreads to a tissue to cause secondary viremia e.g. meninges, CNS, skin, muscle

Question 20

What are the two types of viremia?

Answer 20

Where the virus is free in the plasma or where the virus is associated with a cell

Question 21

What happens in primary and secondary viremia?

Answer 21

In primary viremia there is the initial infection in the blood only in a small amount, in secondary viremia the virus replicates in a target organ and then re-enters the blood at a larger amount

Question 22

What happens if smallpox infects the foetus?

Answer 22

It will cause death of the foetus

Question 23

What happens if rubella infects the foetus?

Answer 23

Will cause developmental abnormalities

Question 24

How does infection at birth occur?

Answer 24

Through an infected birth canal, faecal contamination during birth or viremia

Question 25

Why do certain viruses infect only certain species/tissues?

Answer 25

availability of receptors for the virus

Question 26

Why does the rhinovirus only cause upper respiratory tract infections?

Answer 26

Requires a certain temperature to replicate only available in the upper airways

Question 27

What virus has stability in extreme pH?

Answer 27

rotavirus

Question 28

How do HIV and measles access many tissues?

Answer 28

By replicating in macrophages and lymphocytes

Question 29

Why is it important whether the virus exits the cell at the apical or basolateral surface?

Answer 29

Viruses that exit at the apical surface will find it more difficult to infect deeper tissues

Question 30

What enzyme does the influenza virus require?

Answer 30

tryptase Clara secreted by cells in the large airways

Question 31

How do viruses cause disease?

Answer 31

Either by direct action of virus or as a consequence of the immune response

Question 32

How does poliovirus cause paralysis?

Answer 32

By killing neurons in the spinal cord due to viral replication

Question 33

How does rhinovirus cause loss of cell function?

Answer 33

Causes cilial stasis

Question 34

What cytokines cause fever?

Answer 34

IL-1 and TNF

Question 35

How does dengue fever cause shock?

Answer 35

By internalising virus-Ab complexes into the macrophage which enhances the infection

Question 36

What is the rash in measles due to?

Answer 36

Accumulation of CD4 T cells

Question 37

How does RSV cause bronchiolitis?

Answer 37

By inducing cytokines that recruit eosionophils

Question 38

How does hepatitis B cause liver damage?

Answer 38

Leads to our own CD8 T cells killing hepatocytes

Question 39

What are the symptoms of liver damage?

Answer 39

Yellow eyes and skin

Question 40

What happens in molecular mimicry?

Answer 40

After the virus is gone antibodies attack own proteins which are similar to the virus

Question 41

What viruses lead to immunosuprresion?

Answer 41

HIV and measles

Question 42

What is the result of immunosuppresion?

Answer 42

Susceptible to secondary infections