Magor- Lecture 2: Viral lifestyles and pathogenesis

Question 1

What does a virus need to initiate an infection?(3)

Answer 1

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

Question 2

Sites of viral entry (5) into the host and examples of diseases

Answer 2

1. Aerosol transmission
   -Coronavirus
   -Rhinovirus
   -Influenza
   -Measles
2. Oral-fecal transmission
   -Poliovirus
   -Norovirus
3. Arthropod vector
   -West Nile virus
   -Yellow fever
4. Sexually transmitted
   -HIV
   -Herpes
5. Contact with blood/secretions
   -Hepatitis B virus
   -Rabies
   -Ebola
   -Mpox

Question 3

Acute infections

Answer 3

Rapid and self limiting

Question 4

Example of acute infections

Answer 4

• rhinovirus
• rotavirus
• influenza virus
• coronavirus
• poliovirus

Question 5

TRUE or FALSE

Virus can be present before symptoms

Answer 5

TRUE

Question 6

Influenza

Answer 6

• an acute infection rapidly spread by aerosolized droplets
• the 1918 influenza pandemic killed 40 million people worldwide.

Question 7

Most SARS-CoV2 transmission occurs through

Answer 7

Aerosols- aerosolized droplets that contains particles of virus.

Question 8

Persistent infections

Answer 8

are on-going infections

ex: Hepatitis B

Question 9

Hepatitis B has 2 different lifestyles:

Answer 9

• can either be an acute infection that gets cleared
• persistent infection that never gets cleared

Question 10

TRUE or FALSE

Viruses can persist and overwhelm the immune system later

Answer 10

TRUE

Question 11

Why is it an advantage for a virus to have a persistent lifestyle?

Answer 11

The virus can just hangout and then infect the person for their entire life.

Question 12

Two types of Hepatitis B infection

Answer 12

1. Acute HBV
2. Chronic HBV

Question 13

Acute HBV

Answer 13

• fever
• loss of appetite
• nausea
• vomiting
• abdominal pain
• yellow coloring of the eyes
• dark urine
• clay colored or light stools

Question 14

Chronic HBV

Answer 14

symptomatic or not, approximately 5-10% of adults and 95% of perinatally infected infants are unable to clear the virus, thus becoming chronic carriers.

Question 15

HBV is transmitted in _________________

Answer 15

infected blood

Question 16

In many parts of Asia, there are already many chronic HBV carriers & most people get infected at birth through the exchange of blood between the mother & baby. If you get infected at birth, ____% will be chronic carriers.

Answer 16

95%

Question 17

Case Study: A patient complains of fever, nausea and loss of appetite. On examination you notice yellow whites of eyes. You also notice a tattoo that seems recent enough to still have scabs/bleeding. You suspect a hepatitis B infection.

1. What are the tools for diagnosis of this infection?
2. How long until you can make a conclusive diagnosis?

Answer 17

1. Can do blood test- PCR
2. Quickly

Question 18

Latent infections

Answer 18

an extreme persistent infection (sometimes hidden)

symptoms may not always be present while virus is infectious

viruses hide from the immune system in a latent infection

Question 19

Example of a latent, reactivating infection

Answer 19

Herpes simplex virus

Question 20

Difference between a latent and persistent virus

Answer 20

A latent virus is a persistent virus but it has times where it’s not actually replicating

Question 21

Herpes simplex I virus

Answer 21

• can remain latent for years
• forever; we don’t get rid of Herpes
• 20% of the population have recurrent symptoms
• Herpes simplex hides in the trigeminal ganglia and can reactivate when you are stressed. Nerves are typically protected from immune responses

Question 22

Slow viruses

Answer 22

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

Question 23

Examples of slow virus infection

Answer 23

• Measles SSPE= measles subacute sclerosing panencephalitis
• HIV

Question 24

Measles

Answer 24

• causes acute infection and a rare latent disease
• can be cleared
• human-only pathogen- It’s a pathogen for which we have a really good vaccine
• rash, hypersensitivity reaction, fever, cough, conjunctivitis
• only once in a lifetime
• Measles impairs B cell memory to other vaccines and pathogens

Question 25

How HIV get transmitted?

Answer 25

Many people don't know that they're infected with HIV for years

Question 26

What makes measles so contagious?

Answer 26

1. Extremely contagious for unvaccinated. Up to 90% of the unvaccinated people who come into contact with a contagious individual will also become infected. The measles virus can remain in the air for up to two hours after an infected person leaves an area. 2. Measles has long incubation period. In infected people, the time from exposure to fever is an average of about 10 days, and from exposure to rash onset is about 14 days -but could be up to 21 days. In addition, infected people are contagious from 4 days before rash starts through 4 days after. That's a long period of time where they could unknowingly infect others.

Question 27

Measles have an ________ effect where if a kid gets measles (say at 5 yrs old) it wipes out their B cell response.

Answer 27

immunosuppressant The primary repertoire of B cells that they make is not complete after a measles infection. They lost the immunity to everything that they've previously been vaccinated to.

Question 28

Andrew Wakefield

Answer 28

- connected MMR vaccine to Autism - person who started the anti-vaccine movement

Question 29

Pathogenesis: Injury caused by viruses (3)

Answer 29

1. Cytopathic effects on cells directly -cells may be lysed 2. Viruses can ne oncogenic (cause cancer) -cells lose contact inhibition and their normal interactions (anchorage-independence) and become immortal -can be transformed by virally encoded oncoproteins (v-oncogenes) -viral disruption of host genes (c-oncogenes) 3. Immunopathology- damage as a result of local inflammation

Question 30

Poliomyelitis

Answer 30

- damage caused by viruses - paralysis in 1% of infected individuals - children used to be exposed to polio from their mothers while they were still getting maternal antibodies in breastmilk. - in early 1900s there was an increased incidence because of improved sanitation. This was because infants were not exposed to poliovirus while still protected by maternal antibodies.

Question 31

Cytopathic effect in poliovirus

Answer 31

Cell rounding and lysis by poliovirus infection

Question 32

Anchorage independence

Answer 32

cancer cells lose their attachments and become mobile

Question 33

Peyton Rous

Answer 33

- In 1965, 55 years after his discovery of RSV, he was awarded a Nobel Prize in recognition of the key role that the virus has played in unlocking the secrets of cancer.

Question 34

Retroviruses

Answer 34

- can take up cellular DNA. They integrate a provirus form into the genome

Question 35

Rous sarcoma virus

Answer 35

- has taken up a src gene, called v-src to distinguish it from cellular scr.

Question 36

Src

Answer 36

- a cell signalling molecule that phosphorylates proteins involved in signal transduction. Unregulated cell signalling from v-src causes cancer