Viral Pathogenesis

Question 1

What does a virus need to initiate an infection?

Answer 1

1. Sufficient virus at site of entry
2. Host cells must be susceptible
3. Host cells are permissive (factors needed for replication and dissemination)
4. Local antiviral defense must be breached

Question 2

What does it mean for a cell to be susceptible?

Answer 2

Susceptible cells have receptors required for viral entry

Question 3

What are some viral entry sites?

Answer 3

Aerosol transmission
Oral-fecal transmission
Sexually transmitted
Arthropod vector
Contact with blood/secretions

Question 4

What will stomach acid degrade?

Answer 4

Membrane viruses

Question 5

What is R0?

Answer 5

The number of people an infected person can pass the virus onto

Question 6

What are acute infections like?

Answer 6

Rapid and self-limiting
The virus can be present before symptoms

Question 7

What are some viruses that cause acute infections?

Answer 7

Rhinovirus
Rotavirus
Influenza
Coronavirus
Poliovirus

Question 8

How is influenza spread and what type of infection is it?

Answer 8

An acute infection spread by aerosolized droplets

Question 9

How long can viruses remain infectious on surfaces?

Answer 9

As long as they are wet

Question 10

What are persistent infections like?

Answer 10

On-going infections
Viruses can persist and overwhelm the immune system later

Question 11

What is an advantage of a virus with a persistent lifestyle?

Answer 11

The virus doesn’t have to find a new host for a long time

Question 12

What virus causes persistent infections?

Answer 12

Hepatitis B

Question 13

What type of infections can hepatitis B be?

Answer 13

Acute or persistent

Question 14

What are the symptoms of acute HBV?

Answer 14

Fever, loss of appetite, nausea, vomiting, abdominal pain, yellow colouring of the eyes, dark urine, clay-colored or light stools

Question 15

What percentage of people with acute HBV fail to clear it?

Answer 15

5%

Question 16

What percentage of people clear chronic HBV?

Answer 16

5-10% of adults
95% of perinatally infected infants

Question 17

What might people with chronic HBV develop?

Answer 17

Chronic hepatitis
Permanent liver damage
Liver cancer

Question 18

How can we diagnose an HPV infection?

Answer 18

PCR, antigen screen

Question 19

What are latent infections like?

Answer 19

An extreme persistent infection that can hide from the immune system

Question 20

What is an example of a latent, reactivating infection?

Answer 20

Herpes simplex complex

Question 21

Where does herpes simplex hide?

Answer 21

In the trigeminal ganglia and can reactive when you are stresses as nerves are typically protected from immune responses

Question 22

What percentage of the population has recurrent symptoms of herpes?

Answer 22

20%

Question 23

What is a worry with latent infections?

Answer 23

Symptoms may not always be present while virus is infectious

Question 24

What are slow infections like?

Answer 24

Slow viruses have a long latency period followed by acute infection
The virus may be present at times during latency (HIV) or undetectable for years (measles SSPE)

Question 25

What is SSPE?

Answer 25

Measles subacute sclerosing panencephalitis

Question 26

What types of infections does measles cause?

Answer 26

Acute infections and a rare latent disease

Question 27

What are the symptoms of measles?

Answer 27

Rash, hypersensitivity reaction, fever, cough, conjunctivitis

Question 28

Why is measles so contagious?

Answer 28

The virus can remain in the air for up to 2 hours after the infected person leaves an area
It has a long incubation period, people are contagious 4 days before the rash starts through four days after

Question 29

What are some injuries that can be caused by viruses?

Answer 29

1. Cytopathic effects on cells directly = cells may be lysed
2. Viruses can be oncogenic
3. Immunopathology = damage as a result of local inflammation

Question 30

How can viruses be oncogenic?

Answer 30

Cells lose contact inhibition and their normal anchorage-independence interactions and become immortal

Can be transformed by virally encoded oncoproteins

Viral disruption of host genes

Question 31

What is poliomyelitis?

Answer 31

Paralysis caused by poliovirus, affects 1% of infected individuals as the virus becomes neurotrophic and causes rupture of neurons

Question 32

Why was there an increased incidence of poliomyelitis in the early 1900’s?

Answer 32

Sanitation improved so babies were not exposed to poliovirus while still protected by maternal antibodies

Question 33

What effect can develop from poliovirus?

Answer 33

Cytopathic effect = cell rounding and lysis

Question 34

What are avian cells transformed by?

Answer 34

Two forms of Rous sarcoma virus

Question 35

What does loss of contact inhibition mean?

Answer 35

Cells normally do not pile up on each other and start piling up

Question 36

What does anchorage independence mean?

Answer 36

Cancer cells lose their attachments and become mobile

Question 37

What did the filtration of sarcomas in chickens prove?

Answer 37

That tumorigenesis was not due to a primitive transplantation-like effect but rather a virus

Question 38

What do viral oncogenes cause?

Answer 38

Cancer

Question 39

What can retroviruses do?

Answer 39

Take up cellular DNA and integrate a provirus form into the genome

Question 40

What does Rous sarcoma virus take up?

Answer 40

A src gene that is used as a cell signalling molecule that phosphorylates proteins involved in signal transduction
Unregulated cell signalling from v-src causes cancer