Viruses and Disease Flashcards
What are viruses and their size?
Obligate intracellular paraites that contain EITHER DNA or RNA and are not susceptible to any antibiotics.
Viruses are smaller than bacteria
Describe the structure of a virus and how this limits the size of the genome
Small genome is limited by the capsid (protein coat) - made up of repeated subunits of virally encoded protein
Some viruses also have a lipid envelope - derived from host cell the virus grew in - surrounding the capsid
Viral protein spiked may protrude from capsid/lipid envelope
What is adenovirus and how does it assemble?
Cause sore throats, conjunctivitis, etc.
Has to make only 3 proteins before it self-assembles
Give an example of a virus and how it attaches to a host cell
Influenza and cell of respiratory tract:
Cell has various normal proteins inserted into membrane
Virus interacts with specific receptors in target cell using ligands
How do viruses enter host cells? How can an antiviral affect this?
Viral and cell membrane fuse
OR
By pinocytosis (if virus is not enveloped) - bind to receptor initiates internalisation of both receptor and virus.
Antiviral can inhibit entry by fusion
What does uncoating of a virus involve? How can an antiviral work here?
Viral nucleic acid released from capsid
Antiviral can work by inhibiting ion pump in virus capsid responsible for uncoating
How does the virus replicate with the cell?
Nucleic acid is used to produce new viral proteins (uses host ribosomes and maybe polymerases)
Viral nucleic acid is replicated into progeny genomes
Some viral enzymes may be used, e.g: protease, RNA dependent RNA polymerase
How is the virus assembled?
By packing nucleic acid and proteins together
No antivirals target this step
How are viruses released from a host cell?
By budding - mature progeny virus released with envelope derived from host cell membrane around capsid
By lysis - viruses accumulate until cell lyses. Large aggregations of virus (crystals) may be visible under light microscope as INCLUSIONS
What are antibiotics, their objectives and the structures they target?
Active against bacteria, not viruses and objective is selective toxicity
Structures targeted include bacterial ribosomes (with erythromycin), growing bacterial cell wall (with penicillin) and other bacterial structures, like enzymes
Viruses have few of these targets
What are anti-microbials?
More general term for drugs meant to treat infection that may be bacterial, viral, fungal or protozoal, etc
List possible targets of antiviral drugs
Viral nucleic acid polymerases
Other viral enzymes (involved in viral nucleic acid replication/protein synthesis)
Uncoating (ion pumps can be selectively blocked)
Attachment/entry
Release
Describe DNA and RNA containing viruses
Containing DNA - go to nucleus
Containing RNA - go to cytoplasm (always bring 1 enzyme used in genome replication)
What is meant by rational drug design?
Use of detailed molecular analysis of viral targets to design molecules that may inhibit viral function, rather than blind testing of random molecules for antiviral properties
What is meant by pathogenesis in relation to viruses? What mechanisms occur?
Mechanism by which viruses causes disease:
Cell death due to lysis or cell machinery hijacking
Cell death due to immune system, particularly cytotoxic T cell
Cell proliferation (viruses that cause warts)
Describe viral infection and what increases the risk of infection related cancers
Person can be infectious even if they have no symptoms. Immunosuppression increase incidence of infection related cancer, like Kaposi’s sarcoma
Virally induced cancers - HPV and cervical cancer, Hep B & Hep C and hepatocellular carcinoma
Immune response to viral infection?
Cytotoxic T lymphosytes recognise viral proteins on host cell surface as foreign and induce apoptosis of infected cell
Neutralising antibodies (IgG, IgM) can prevent virus binding to cellular receptors
What type of immunity is most important against viral infection?
Cell mediated immunity (does not involve antibodies, but does involve phagocytes, cytotoxic T cells, etc) more so than humoral immunity (involving antibodies) - antibodies however do have a role in long term adaptive immunity
What is meant by persistence?
Viruses can elude immune system and establish infection years
Infections can be intermittent, with periods of active viral replication punctuated by viral latency.
What are examples of persistent viruses and how they function?
Viruses may become latent (no active replication ) and reactivate, like Herpes Simplex virus
Viruses may remain continually active for years. Chronic infection can result, HIV and Hep C. (Patients may remain asymptomatic - no symptoms - before getting fatal complications)
How are viruses detected in the lab?
Detect antibody response against virus
Detect presence of virus itself
What specific techniques are used to detect viruses?
PCR (detects viral nucleic acid) and NAATs (Nucleic Acid Amplification Techniques)
Antigen detection
How can recent infection be differentiated from past infection?
Detection of virus specific IgM antibodies
Detection of rising titre of IgG antibodies
Detected of very high titre of IgG antibodies
