Anti Viral Agents

Question 1

What is a virus

Answer 1

An infectious obligate intracellular parasite
Dependant on cell machinery of host to replicate

Question 2

Sizes of viruses

Answer 2

From 10nm to 1 um

Question 3

What do non-enveloped viruses have as an outside layer?

Answer 3

Protein capsid e.g. adenovirus, picornavirus, calicivirus

Question 4

What do enveloped viruses have as an outside layer

Answer 4

Lipid envelope derived from host membrane

Can be pleiomorphic e.g. measles virus

OR typical shape like ebola

Question 5

Central dogma

Answer 5

DNA is converted by transcriptase into RNA which is translated into proteins by ribosomes

Question 6

Reverse transcriptase

Answer 6

Makes DNA from hosts nucleotides using virus rna

Question 7

Rna is negative sensed

Answer 7

Complementary strand of mrna
Before translating genome into proteins they copy the negative sense back into the positive sense

Question 8

Do RNA viruses & Retroviruses use their own machinery to replicate? and how does this affect their mutation rate?

Answer 8

They use their own polymerase to replicate

These lack proof reading, so higher mutation rate

Question 9

How do RNA viruses compensate for RNA genomes being shorter than DNA genomes

Answer 9

Use complex coding strategies to make more proteins than expected from small RNA genome e.g. overlapping reading frames

Question 10

Dna viruses

Answer 10

Have genomes up to 100s kb
Have accessory genes which can modify immune response so however these are often lost as there is no immune system in cultured cells

Question 11

Segemented genomes

Answer 11

Allow reassert ent

Question 12

Generic virus replication cycle

Answer 12

1. Virus contains nuclear capside which contains its genome
2. Virus attaches to specific virus receptor cell surface, infecting the cell
3. Once inside, capsid falls away, exposing genome to cell machinery
4. Genome can be converted into mRNA, or it may be mRNA itself
5. This is translated by host cell ribosomes into proteins
6. Viral genome can utuilise self polymerase or host cell polymerase to create new proteins

Question 13

HIV replication cycle

Answer 13

1. HIV virion binds to cell surface receptor CD4 with its gp120 spike protein
2. Virus is brought closer to cell surface, engages with coreceptor CXCR4 or CCR5
3. Virus membrane and host cell membrane fuse and release core of virus particle
4. This undergoes reverse transcriptaseof the RNA genome → dsDNA + integrase → spliced into host’s own DNA
5. Viral genome is transcribed into mRNA → codes for viral proteins and RNA
6. These assemble and bud out of the cell to infect other cells

Question 14

Influenza replication cycle

Answer 14

1. Virus particle spikes latches onto glycoproteins adn glycolipids
2. Virus is endocytosed into host cell
3. Viral particle fuses envelope with endosomal lipids → releasing genomic segments of negative sense RNA
4. These enter nucleus, where RNA dependent RNA polymerase turns them into mRNA → replicates them into new genomes
5. mRNA leaves nucleus and picked up by ribosomes → makes new proteins
6. New genomes move to cell surface alongside proteins of virus where they bud out of the cell
7. For every 1 virus that enters the cell 100-1000 leave the cell

Question 15

Cytopathic effect

Answer 15

Result of virus lysing the cell
Could be due to accumulation of viral proteins

Question 16

What do viruses form in cell monolayers

Answer 16

A plaque where virus kills a bunch of cells in the middle

Question 17

How can you find out how many virus particles are in a particular preparation of virus?

Answer 17

Making dilutions and putting them onto monolayers of cells

After 2/3 days, count number of plaques formed

Question 18

Syncytia

Answer 18

Some viruses with surface proteins that can fuse at neutral pH often fuse cells together

Syncytia assay is also a method of finding out how may virus particles there are in a certain sample

Question 19

How can viruses be detected

Answer 19

• Detecting viral genome PCR, RT-PCR
• Detecting viral antigen IFA, ELISA
• Detecting virus particles EM, HA
• Detecting virus cytopathic effect in cultured cells (virus isolation)

Question 20

Why is RT-PCR used to detect SARS CoV2?

Answer 20

SARS CoV2 only contains RNA

Question 21

Therapeutic index

Answer 21

Ratio between how much drug you have to use in order to control the virus and the amount that makes a person feel ill from the side effects of the drug

Question 22

Targets for antiviral drugs

Answer 22

Viral enzymes
Some act as nucleoside analogues to inhibit or interfere with nucleic acid replication
Some drugs target specific viral factors

Question 23

Acyclovir

Answer 23

Targets herpes virus
Is a nucleoside (guanine) analogue which lacks 3’ hydroxyl group preventing phosphodiester bind formation and
Onl activate in virus infected cells
The thymidine kinase that phosphorylates acyclovir monophosphate only formed by heroes family
Resistance is rare but causes by mutation in thymidine kinase

Question 24

Remdesivir

Answer 24

Analogue of adenosine causes chain termination of 3 nucleotides downstream as it twists the shape
Made for hep c tested against Ebola but didn’t work

Question 25

Amantadine/rimantadine

Answer 25

Influenza a target
Blocks M2 channel so protons from endosome can’t enter virus and so virus is locked preventing virus uncoating
Single point mutation in S31N encoding for M2 channel can cause resistance
Most H3N2, H5N1 and H1N1 strains are resistant

Question 26

Taimflu (oseltamivir)

Answer 26

Influenza
Inhibits neuraminidase enzyme that cleaves sialic acid from the infected cells surface preventing spread of new virus particles

Question 27

Baloxavir

Answer 27

Influenza
Inhibits PA endonuclease subunit of viral RNA polymerase
Resistance occurs by single point mutation I38T
It decreases viral shedding which can interrupt transmission

Question 28

Hepatitis c

Answer 28

Relied on interferon treatment with ribavirin which was only effective in 50% of patients

Question 29

Hepatitis c meds

Answer 29

NS3/4A protease inhibitors (PIs)
Inhibit post-translational processing of viral proteins by inhibiting NS3/4A serine protease

NS5A inhibitors
Inhibit viral rna replication

NS5B nucleoside polymerase inhibitors (NS5B inhibitors) and NS5B non-nucleoside polymerase inhibitors (NNPIs)
Inhibit rna dependant rna polymerase NS5B to inhibit conversion of + to - sense viral RNA

Question 30

Antivirals against HIV

Answer 30

Inhibiting entry of virus by stopping it from attaching to its receptors and co-receptors

Inhibit fusion of viral and host cell membrane

Targeting reverse transcriptase

Target integrase

Target proteases unique to viruses

Question 31

Why is there no cure for hiv

Answer 31

HIV is a retrovirus so integrates its genomic material into host cell DNA so there are always reservoir cells in HIV patients even if they take those antivirals against it that carry the viral DNA
Only two people have been cured

Question 32

How were two people cured of HIV

Answer 32

Both of these had leukemia so got bone marrow transplants → doctors transferred marrow from naturally HIV resistant people who had mutation in CCR5 coreceptor gene (a Delta 32) which means CCR5 not expressed so HIV can’t enter new cells

Zidovudine is a nucleoside analogue used to treat HIV

Question 33

Biologicals

Answer 33

Passive immunotherapy- antibodies taken from recovered individuals, or produced in the laboratory from immortalised B cells

Question 34

Dexamethasone

Answer 34

Corticosteroid used for immunosuppressants

Question 35

Toculizimab

Answer 35

Targets pro-inflammatory cytokine IL-6

Question 36

Future forantiviral therapy

Answer 36

• New antiviral therapies that target host
• Combinations of drugs with different targets
• Broad acting antivirals
• Delivery systems suitable for target population e.g. oral ones > IV in terms of what patients prefer
• Diagnostics to justify antiviral use

Question 37

HIV meds

Answer 37

CCR5 co receptor antagonist-inhibits viral entry
Fusion inhibitors-inhibit viral entry
NRTIs or NNRTIs-inhibit HIV reverse transcriptase to inhibit viral dna synthesis
INSTI-inhibit integration of viral dna into host genetic
Protease inhibitors-inhibit cleavage of hiv by proteases
PrEP is an NRTI

Question 38

Why is neuroaminidase important

Answer 38

Cleaves bond between haemagluttinins on influenza and sialic acid allowing virus to continue infecting more cells,essential for viral release