Patterns of viral infection

Question 1

Latrogenic transmission

Answer 1

Health care worker e.g. contaminated needles

Question 2

Noscomial transmission

Answer 2

Acquired in hospital

Question 3

Vertical transmission

Answer 3

From parent to offspring

Question 4

Horizontal transmission

Answer 4

All other forms

Question 5

Germ line transmission

Answer 5

Part of the host genome (e.g. intergrated retrovirus)

Question 6

Viral routes of entry to the body

Answer 6

Skin
Mucosal surfaces (Respiratory, Enteric, Genital tract)
Conjunctiva
Blood
Bites

Question 7

Arboviruses

Answer 7

Viruses spread by insects

Question 8

Dissemination from site of entry

Answer 8

Local infection
Primary viraemia
Amplification
Secondary viraemia
Target organ

Question 9

Viraemia

Answer 9

Virus in blood

Question 10

Viral rashes

Answer 10

Sign of systemic viral infection
Virus leaves blood and enters skin
Cells destroyed by virus replication

Question 11

Example of viral rash

Answer 11

Koplik spots in mouth (measles)

Question 12

When do symptoms of Varicella Zoster virus (chicken pox) appear?

Answer 12

After secondary viraemia

Question 13

Varicella zoster virus mechanism of action

Answer 13

Enters body through respiratory route
Can infect many cell types including skin cells.
Leads to mild self-limiting illness in most childhood cases.
From the skin site, it can infect sensory neurones where it remains latent.

Question 14

What happens in herpes zoster, or shingles, occurring in adulthood when cellular immunity is impaired?

Answer 14

Varicella zoster virus is reactivated in the sensory neurone and causes a painful rash at nerve endings

Question 15

Tropism

Answer 15

predilection of viruses to infect certain tissues and not others

Question 16

What 3 factors are tropisms based on?

Answer 16

Susceptibility: receptor interactions
Permissivity: ability to use the host cell to complete replication
Accessibility: ability of the virus to reach the tissue

Question 17

Describe the type of tropism exhibited by HIV

Answer 17

Viral attachment protein GP120 on HIV interacts with CD4 on the T cell
It attaches to co-receptors CCR5 and CXCR4

Question 18

What mutation confers resistance to HIV in exposed uninfected?

Answer 18

Delta 32 mutation in CCR5

Question 19

Describe the type of tropism exhibited by Measles.

Answer 19

Bind to SLAM on immune cells when entering the host

Bind to Nectin 4 on airway epithelia when leaving the host

Question 20

Describe the type of tropism exhibited by Influenza.

Answer 20

Haemagglutinin on influenza binds to sialic acid that are ubiquitous to gain entry through endosomes
Low endosomal pH allows conformational change required for virus to fuse with the endosome membrane and uncoat
The cleaving of the protein of the virus is essential for the viral genome to gain access to the host cell genetic material
So can only infect cells with the necessary proteases to cleave the protein

Question 21

Pathogenicity

Answer 21

ability of the virus to cause disease

Question 22

Virulence

Answer 22

capacity of a virus to cause disease

Question 23

Patterns of virus infection

Answer 23

Acute infection followed by viral clearance
Acute infection but ‘accidental’ tissue infected with permanent damage despite viral clearance
Persistent infection: latent, slow, transforming
Long incubations
Oncogenesis

Question 24

Acute infection and clearance

Answer 24

e.g. Colds and influenza.
Many unapparent or asymptomatic infections.
Adaptive immune response provides immunity
Viruses continue to circulate in populations by antigenic variation

Question 25

Acute infection and death

Answer 25

Smallpox (Variola virus) Infection of skin. Viral growth factors induce proliferation of skin resulting in pox. Dengue haemorrhagic fever. Leakage of blood plasma from capillaries. Tendency to severe bruising, and bleeding.

Question 26

Acute infection and accidental pathogenesis examples

Answer 26

Poliovirus (localised infection of small intestine) | Rubella (mild rash)

Question 27

How does poliovirus lead to accidental pathogenesis?

Answer 27

may lead to Poliomyelitis: Neurovirulent virus, infects motor neurons causing paralysis.

Question 28

How does Rubella lead to accidental pathogenesis?

Answer 28

In early stage fetus virus has a strong tropism for dividing neuronal tissue. Leads to a classic triad: 1. Deafness 2. Eye abnormalities (cataracts) 3. Congenital heart disease

Question 29

Examples of persistent viral infections | hide in places immune system struggles to reach

Answer 29

Papillomaviruses in warts. Chronic carriers of hepatitis B and C viruses. Herpes viruses e.g. Herpes Simplex, Varicella Zoster

Question 30

Strategies for viral persistence

Answer 30

Evading immune surveillance e.g. Hepatitis C | Infecting tissues with reduced immune surveillance (CNS and skin) e.g. Herpes, papillomavirus

Question 31

Describe the latency of Herpes simplex virus.

Answer 31

Can remain latent on nerve cells and then become activated in an attack of shingles The virus then moves to the end of the neurones and replicates through the skin (forming a cold sore)

Question 32

Give 4 examples of oncogenic viruses and the types of cancer that they cause.

Answer 32

HHV8: Kaposi Sarcoma HTLV-1: Leukaemia Merkel Cell Polyoma Virus: Merkel Cell Polyoma HPV: Cervical Cancer

Question 33

Why would viruses encode oncogenes?

Answer 33

Enables them to interfere with the cell cycle in order to enhance their own replication

Question 34

What type of cancer do Hepatitis B and C cause?

Answer 34

Hepatocellular Carcinoma

Question 35

What types of cancer can Epstein-Barr Virus cause?

Answer 35

Burkitt’s Lymphoma Hodgkin’s Lymphoma Nasopharyngeal Carcinoma

Question 36

What is Epstein Barr Virus?

Answer 36

A gamma herpes virus, the most common virus infection of mankind. In most, causes a lytic infection in childhood or infectious mononucleosis in young adulthood. Remains latent in B cells. Passed on in saliva.

Question 37

What effects the outcome of viral infections?

Answer 37

Viral sequence and load Host immune response, co-morbidity, genetics and age Co-infections

Question 38

Give an example of viral load affecting the outcome of an infection.

Answer 38

2nd child in a household infected with chicken pox will have a worse infection because they’ll get a large dose from the first child

Question 39

Give 2 examples of co-infections affecting the outcome of an infection.

Answer 39

HHV8 can cause Kaposi Sarcoma in people who are infected with HIV (immunocompromised) Hepatitis Delta Virus only infects people with Hepatitis B

Question 40

Give an example of viral sequence affecting the outcome of an infection.

Answer 40

2 strains of poliovirus might vary in their virulence. Single mutation in genome can mean 1 strain acts as a live attenuated vaccine (Sabin) Another invades the motor neurone & causes flaccid paralysis (poliomyelitis).

Question 41

What can determine the outcome of a hepatitis C infection?

Answer 41

KIR genotype

Question 42

Predisposing co-morbidities and conditions for severe influenza

Answer 42

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