MICRO: Viral Infections

Question 1

3 shapes of viruses

Answer 1

• helical
• icosahedral
• complex e.g. bacteriophage

Question 2

structure of a virus

Answer 2

• nucleic acid (DNA/RNA)
• protein coat (capsid)
• may have lipid or protein envelope

Question 3

how do viruses replicate?

Answer 3

• attach to specific receptors and enter host cell
• shed capsid to release genetic material
• host produces viral proteins which makes new viruses once capsid forms
• viruses exit the cell, some take the plasma membrane of host cell > forms envelope and some lyse the cell

Question 4

outcomes of viral infection

Answer 4

• oncogenesis: normal cells turn into tumour cells by activating oncogenes or inhibiting tumour suppressors
• cytopathy: direct destruction of cells
• immunopathology: exaggerated immune response to virus
• latent infection: no immediate harm to cell but reactivates later

Question 5

how does dengue virus hijack cells?

Answer 5

• usually infects monocytes, macrophages, dendritic cells
• Abs from a previous infection bind to virus and monocytes (via Fc region) and trick them into taking up the virus
• leads to cytokine storm

Question 6

what 4 things are the Baltimore classification based on?

Answer 6

• type of nucleic acid
• presence or absence of envelope
• replication method of mRNA (+/-)
• morphology

Question 7

+ve vs -ve sense RNA

Answer 7

• +ve can be translated straight away as mRNA
• -ve needs to be transcribed into +ve sense via RNA-dependent RNA polymerase, and then translated

Question 8

herpesviridae

Answer 8

• enveloped dsDNA
• HSV-1 = oral herpes - transmitted by skin-skin contact w/ lesion
• HSV-2 = genital (STD)
• latent virus cannot be transmitted (HSV-1 in trigeminal ganglia and HSV-2 in sacral ganglia)

Question 9

how does herpesviridae evade the immune response?

Answer 9

• glycoproteins on viral surface: binds and inactivates C3b complement. Can also bind to Fc region of host Ig, blocking it
• once inside cell: vision host shut off protein (Vhs) - degrades hosts mRNA so it only focuses on making viral proteins
• inhibits NK cells, CD8 T cells, interferons (warns other cells), degrades MHC I

Question 10

how can a virus reactivate from latency?

Answer 10

• UV light
• stress, fever, tissue damage
• further infection
• immunosuppressant meds

Question 11

HPV + 2 types + type of infection

Answer 11

• non-enveloped, dsDNA virus
• alpha: genital warts
• beta: skin/oral warts
• transmitted thru direct contact
• not cytotoxic, evades immune response = can remain latent + oncogenic

Question 12

how does HPV evade immune response?

Answer 12

• infects epithelial cells + mucous membrane
• interferes w/ Rb and p53 (tumour suppressor proteins) to prevent apoptosis = mutations and uncontrolled growth > cancer

Question 13

antigenic drift vs shift

Answer 13

• drift: mutations in virus (RNA isn’t checked so higher mutation rate)
• shift: combination of 2 viruses that have coinfected same cell

Question 14

how do DNA vs RNA viruses hijack the host machinery?

Answer 14

• DNA: goes to the nucleus for transcription and then ribosome for translation
• ssRNA: goes to the ribosome for translation (+ve sense) OR makes RNA-dependent RNA polymerase to turn into +ve sense

Question 15

SARS-COV-2

Answer 15

• ssRNA (+) enveloped virus
• corrupts ACE-2 receptor on many cells (regulates BP)
• fluid build up in lungs + cytokine storm

Question 16

hep C
- type of virus
- transmission
- Sx

Answer 16

• ssRNA (+ve) enveloped virus
• blood borne virus, infects hepatocytes
• transmitted from contaminated blood or needles and sometimes sexual contact
• Sx: jaundice, loss of appetite, fatigue, nausea

Question 17

4 outcomes of hep C infection

Answer 17

• acute infection followed by clearance
• clearance followed by superinfection
• reinfection by a 2nd type
• chronic infection

Question 18

HIV

Answer 18

• +ssRNA retrovirus
• bloodborne virus, sexually transmitted, perinatal
• causes lytic and latent infection of CD4+ cells
• causes persistent infection in macrophages

Question 19

what is a retrovirus

Answer 19

• +ssRNA viruses which reverse transcribe RNA into dsDNA
• integrase integrates dsDNA into host genome in nucleus

Question 20

influenza

Answer 20

• -ve sense ssRNA virus
• infects respiratory tract > cytokine storm
• uses haemagglutinin to enter cell and neuraminidase to exit cells > these can mutate (drift)
• has 8 pieces of RNA which can recombine w/ other viruses > antigenic shift

Question 21

ebola

Answer 21

• -ve sense ssRNA virus (enveloped)
• zoonosis from bats > apes > humans
• spread thru contact w/ body fluids
• long incubation period
• can infect >8 cell types = multisystemic infection = hypovolaemic shock = deadly

Question 22

what is a formite?

Answer 22

• inanimate objects which can have a role in the chain of infection (e.g. reservoir)