Microbiology- Viruses and Disease Flashcards
4 components of a virus molecule
protein spikes
protein coat (capsid)
nucleic acid
envelope
Viruses contains RNA and DNA. T/F
False
They only contain one or the other as they have a very small genome, which is limited by the capsid
What comprises the protein coat?
repeated subunits of virally encoded protein
Where is the lipid envelope derived form?
The host cell which the virus grew in
Limitation of microscopy
Only tells you the shape of a microbe, which may be indistinguishable from others in its group
How does a virus become phagocytosed?
- Attachment
- Entry
- Uncoating
- Nucleic acid and protein synthesis
- Assembly
- Release
How does a virus attach to a cell?
its ligand attaches to specific receptors on target cell
By which process may non-enveloped viruses enter the cell?
Endocytosis
How do enveloped viruses enter the cell?
By fusion of viral and cell envelopes
What is endocytosis
binding to receptor initiates internalisation of both the receptor and the virus
Uncoating
Viral nucleic acid is released from capsid due to viral ion pump
Nucleic acid and protein synthesis
Nucleic acid is used as instructions to produce new viral proteins - host ribosomes are ALWAYS used and host polymerases may be used.
Viral nucleic acid is replicated into progeny genomes
Assembly
Nucleic acid and proteins packaged together
Inclusions
crystals of assembling virus may be seen under light microscopy
Release
A piece of the host membrane ends up around capsid ie reverse of entry process
Release by budding
Mature progeny virus released with envelope derived from the host cell membrane.
NOT ALL VIRUSES RELEASED LIKE THIS
Release by lysis
virus breaks down the cell
Antibiotics are active against viruses. T/F?
False
only active against bacteria
Objective of antibiotics
Selective toxicity
How do antivirals inhibit entry?
Via fusion, mediated by viral enzyme
How do antivirals inhibit uncoating?
they inhibit the ion pump in the virus capsid
How do antivirals inhibit assembly?
No antivirals target this step yet
Rational drug design for antivirals
the use of detailed molecular analysis of viral targets to design a molecule that might inhibit its function, rather than blind testing of random molecules for antiviral properties
In which setting is antiviral resistance most seen?
long periods of treatment eg immunocompromised patients
How is antiviral resistance analysed?
genotypically
- the phenotype can be inferred from genotype
can also be done phenotypically ie green in vitro in presence of drug
How to establish if a newly discovered virus is a pathogen?
Case-control study
- One group with clinical signs of infection
- Second group as similar as possible to the first group, except that they are well
- Compare prevalence of virus in the cases and the controls
Role of cytotoxic T lymphocyte in immunity and virus infection
recognise proteins on the cell surface as being foreign and will signal the infected cell to commit suicide in order to prevent the formation of further mature virus
Examples of neutralising antibodies and their role in immunity and infection
IgG, IgM
Bind to cell receptors
Cell mediated immunity is generally more important than humoral immunity in providing recovery from viral infection, though antibodies have a clear role in long term adaptive immunity
Quiescent
Becomes latent but may reactivate
eg Herpes simplex virus, Varicella-zoster virus
Examples of continually active viruses/ chronic infections
- HIV
- Hep C
How to confirm viral infection in lab
detect antibody response to virus and the virus itself
Ways in which recent and past infection can be differentiated?
Detection of:
- virus specific IgM
- rising titre of IgG
- very high titre of IgG
Paired blood samples may be needed ie acute and convalescent
Virus detection methods
PCR
Antigen detection
- cultures, EM
