Microbiology 5

Question 1

List the types of transmission of virus

Answer 1

• Respiratory
• Fecal oral
• Contact
• Zoonoses
• Blood
• Sexual contact
• Maternal-neonatal
• Germ line

Question 2

What are fomites?

Answer 2

Snot.ect from a surface when an infected person touches them

Question 3

What is intragenic transmission?

Answer 3

Where a health worker is the cause of infection.

Question 4

What is a nosocomial infection?

Answer 4

An infection caught in the hospital.

Question 5

What is vertical transmission?

Answer 5

From parent to offspring

Question 6

What is horizontal transmission?

Answer 6

Any form of transmission not from parent to offspring.

Question 7

What is germ line transmission?

Answer 7

Where the virus is part of the host genome.

Question 8

What is viraemia?

Answer 8

Virus in the blood

Question 9

What are the stages of dissemination from the site of entry?

Answer 9

Local infection to primary viraemia to amplification to secondary viraemia to the target organ.

Question 10

What causes viral rashes?

Answer 10

• Systemic viral transmission
• Virus leaves the blood and enters the skin
• Cells are destroyed by virus replication

Question 11

Define the term tropism.

Answer 11

The predilection of viruses to infect certain tissues and not others.

Question 12

How is tropism determined?

Answer 12

• Can be defined by receptor interactions (susceptibility)
• Ability to use the host cell to complete replication (permissivity)
• Whether the virus can reach a tissue (accessibility).

Question 13

How is the tropism of HIV determined?

Answer 13

• Receptor use - CD4 and CCR5 or CXCR4 co receptors

- Delta 32 mutation in CCR5 leads to HIV resistance

Question 14

What receptors does measles use?

Answer 14

Two receptors - CD155/SLAM and Nectin 4

Question 15

Describe the pathway taken by the measles virus.

Answer 15

• Virus enters new host - binds to SLAM on immune cells resulting in ummunosuppression
• Virus exits from the infected host using nectin 4 on the airway epithelia

Question 16

What determines tropism of HA (influenza) virus?

Answer 16

• The virus enters through endosomes
• Low endosomal pH triggers fusion
• HA cleavage is required for exposure of fusion peptide (conformational change)
• Depends on availability of host proteases

Question 17

Define the term pathogenicity

Answer 17

The ability of the virus to cause disease

Question 18

Define the term virulence

Answer 18

The capacity of a virus to cause disease

Question 19

What does viral disease depend upon?

Answer 19

Viral disease depends on how much replication the virus undergoes but is affected by other factors too such as the host response.

Question 20

What are the different patterns of virus infection?

Answer 20

• Acute infection (followed by viral clearance)
• Acute infection with accidental tissue damage
• Persistence infection - latent& slow& transforming
• Long incubations
• Oncogenesis

Question 21

Define acute viral infection

Answer 21

Rapid onset of disease

Question 22

What are arboviruses?

Answer 22

Viruses spread by insects

Question 23

What is a systemic infection?

Answer 23

Infection through the whole body

Question 24

What is r0?

Answer 24

How many people will be infected by one infected person.

Question 25

What is a latent persistent infection?

Answer 25

An infection that is hiding in the cell waiting to cause an episode of reactivation.

Question 26

Give examples of acute infection

Answer 26

- Colds and influenza. - Many unapparent or asymptomatic infections. - Smallpox (variola virus) and dengue haemorragic fever causes death - Poliovirus can cause poliomyelitis by accident& as can rubella

Question 27

Give examples of persistent viral infections

Answer 27

- Chronic infection with low level replication of viruses in tissues which regenerate. Papillomaviruses in warts. - Chronic carriers of hepatitis B and C viruses.

Question 28

What are the strategies for viral persistence?

Answer 28

- Evading immune surveillance by infecting tissues unlikely to be infected - MHC downregulation - Escape by mutation

Question 29

Give some examples of viruses that use strategies for viral persistence.

Answer 29

- Measles - Herpes - Papillomavirus

Question 30

Give some examples of viruses that use latency.

Answer 30

Herpes simplex virus

Question 31

How does herpes simplex virus latency and reactivation occur?

Answer 31

- Primary site of infection (epithelial cells) - Secondary site of infection and site of latent infection (sensory neuron) - Site of recurrent infection (epithelial cells)

Question 32

How can viruses cause cancer?

Answer 32

- Viruses may encode oncogenes | - May interfere with the cell cycle to enhance their replication

Question 33

Give examples of viruses that cause cancers

Answer 33

- Papillomaviruses encode inhibitors of tumour suppressor genes. This forces the cell into S phase. - Polyoma virus - HTLV-1 causes leukaemia - Hep B and C increase chance of hepatocellular carcinoma - Epstein Barr Virus causes lymphoma/carcinomas

Question 34

What affects the outcome of virus infection?

Answer 34

- Virus sequence - Virus load - Host immune response/status - Host co-morbidity - Co infections - Other medications - Host genetics - Host age & gender

Question 35

Give an example of a virus whose sequence affects the outcome

Answer 35

- Poliovirus - A single mutation in the genome can mean that one strain acts as a live attenuated vaccine - Another invades the motor neurone and causes flaccid paralysis (poliomyelitis).

Question 36

Give an example of a virus whose viral load affects the outcome

Answer 36

First child to be infected with chicken pox has a milder sibling than the second in the family.

Question 37

Give an example of coinfections

Answer 37

- Secondary infection after influenza - HIV infected individuals more likely to get Kaposis Sarcoma - Hepatitis delta virus only affects people with hep B infection.

Question 38

Give some examples of predisposing co-mobidities and conditions for severe influenza.

Answer 38

- Asthmatics and respiratory viruses - Obesity - Immunosuppression - Immunodeficiency - Elderly - Diabetes mellitus - Pregnancy