Canonical Question
Micro Pharm – Antivirals/fungals
Master answer
Baltimore Classification system (for Viruses)
| I | dsDNA viruses | mRNA is transcribed directly from the DNA template | Adenoviruses, Herpesviruses, Poxviruses |
| II | ssDNA viruses | (+ strand or “sense”) DNA DNA is converted to double stranded form before RNA is transcribed | Parvovirus (B19) |
| III | dsRNA viruses | mRNA is transcribed from the RNA genome | Rotavirus |
| IV | (+)ssRNA viruses | (+ strand or sense) RNA Genome functions as mRNA | Picornaviruses (Entero, HepA), Flaviviruses (Dengue) |
| V | (−)ssRNA viruses | (− strand or antisense) RNA mRNA is transcribed from the RNA genome | Orthomyxoviruses (Influenza) |
| VI | ssRNA-RT viruses | (+ strand or sense) RNA with DNA intermediate in life-cycle RT makes DNA from the RNA genome DNA is then incorporated into host genome mRNA is transcribed from the incorporated DNA | Retroviruses (HIV) |
| VII | dsDNA-RT viruses | DNA with RNA intermediate in life-cycle Viral DNA is replicated through an RNA intermediate, the RNA may serve directly as mRNA or as a template to make mRNA | Hep B |
Key:
ss: Single stranded
ds: Double stranded
(-): – strand or antisense
(+): + strand or sense
RT – Reverse Transcriptase
Past Classifications (now not used):
By shape:
- filamentous
- isometric (or icosahedral)
- envelopedH
- Head and tail
By Genome Structure and Core:
- RNA / DNA
- Single-stranded / Double stranded
- Linear/Circular
- Non-segmented/Segmented
By capsid structure:
- Naked icosahedral – Hep A, Polio
- Enveloped icosahedral – EBV, HSV
- Enveloped helical – Influenza, Measles
- Naked Helical – Tobacco Mosaic virus
- Complex – Herper, Smallpox, Hep B
Mechanism of Action: Oseltamivir vs Aciclovir
| Oseltamivir | Aciclovir |
|---|---|
| Neuraminidase inhibitor (Anti-Influenza) | Viral guanosine analogue |
| Prodrug | Prodrug |
| Active metabolite inhibits viral Neuraminidase | Converted to aciclovir monophosphate by viral thymidine kinase which in turn is converted to aciclovir triphosphate by host cell |
| cleaves the sialic acid (which is found on glycoproteins on the surface of human cells that helps new virions to exit the cell) | ACV-TP is HSV-specified DNA polymerase inhibitor |
| prevents viral release by infected cells (viral shedding) | inhibits nucleic acid production, incorporates into DNA resulting in chain termination |
| Active against Influenza | Active against herpesvirus family: HSV-1,2, VZV,EBV,CMV(least) |
Click to Open Pharmacopeia: Antivirals and Antifungals (Level 2)
Mooney / JC 2020
Exam appearances
| Exam | Exact wording | Relationship | Success |
|---|---|---|---|
| 2010A Q12 | Outline the classification of viruses giving examples of each class (60% marks). Describe the mechanism of action of acyclovir and oseltamivir (40% marks). | historical_member | — |