8. What Viruses Are Flashcards
What is a virus?
The viral gennome contains the infomation for initiating and completing an infectious cycle. What does this cycle include?
Give 3 characteristics of viruses that differentiate them from other microorganisms.
A package of genetic information protected by a protein shell for delivery into a host cell to be expressed and replicated.
Attachment, entry of particle, decoding of genome information, translation of viral mRNA by host ribosomes, genome replication, asssembly and release of particles containing the genome.
Nucleic acid (DNA or RNA), lack of nuclear membrane and external cell wall, very small genomes (produce limited numbers of proteins and don’t posess many intracellular systems i.e. they’re parasites).
NB mimivirus has much bigger genome.
What are some global emerging/re-emerging infectious diseases? (viral)
Describe the basic viral structure.
What are the 3 possible arrangements of nucleocapsids?
Describe lipid enveloped viruses.
SARS, Enterovirus, Hep C, Ebola, HIV, Denge, Yellow fever
Capsomeres (structural subunits containing several proteins) aggregate to produce the viral capsid, which associates with the viral nucleic acid to produce a nucleocapsid.
Cubic (e.g icosahedral - herpes), helical (influenza), complex
Lipid envelopes derived from cellular membranes, studded with surface projections (spikes/peplomers), usually glycosylated by host systems prior to make them sticky
Describe HPV and the types.
What are virus-like particles?
Describe how the HPV vaccine works.
Small DNA tumour viruses - about 200 genotypes in humans. Circular dsDNA. Infect epithelial tissue. Types: mucosa-associated (low-risk HPV 6, 11: genital warts. High-risk HPV 16,18: squamous anogenital neoplasias and oropharyngeal cancer) cutaneous (HPV 5,8: cause epidermodysplasia verruciformis and skin cancer)
For vaccination, empty shell - no genome.
Based on hollow VLPs assembled from recombinant HPV coat proteins. Target the 2 most common high-risk HPVs - types 16 and 18 (Cause about 70% cervical cancer).
How is the virus genome protected?
How is the genome delivered?
List 3 of its interactions with the host?
Stable, protective protein shell. Specific recognition and packaging of nucleic acid genome. In some: interaction with host cell membranes to form envelope.
Specific binding to external host cell receptors. Transmission of signals induce genome uncoating. Induction of fusion with host cell membranes. Interaction with internal components of host cell to direct transport of the genome to appropriate site.
Interacts with: cell host components (ensure infectious cycle), cellular components (transport to intracellular assembley site), host immune system
What are the different types of viral nucleic acids?
Describe viral replication.
RNA viruses: ssRNA (+ve (e.g. poliovirus) or -ve polarity), dsRNA (one piece or segmented (e.g. rotavirus))
DNA viruses: ssDNA, dsDNA (e.g. herpes) (hep B = dsDNA circular)
Describe measles.
What are some complications of measles?
Respiratory virus, 10-14 days incubation period. Growth in nasopharynx and regional lymph nodes. 10 viremia 2-3 days after infection. 20 5-7 days afeter with spread to tissue. Airbourne/droplet transmission. Single infection confers lifelong immunity. Vaccine.
Otitis media, diarrhoea, pneumonia, convulsions.
Describe HIV replication.
How can viruses be classified?
How is virus evolution defined?
What are the 4 mechanisms of virus evolution?
Tree, starting with nucleic acid (DNA or RNA) and going down through: symmetry of capsid, naked/enveloped, genome architecture, Baltimore class. Then properties e.g. virion diameter, genome size.
In terms of a population, not an individual virus particle. Populations comprise diverse arrays of mutants produced in huge quantities.
Mutation, recombination, re-assortment, selection.
List some random viral mutations that would be selected for.
Give an example of re-assortment.
Adaptive fine tuning to establish infection in (new) host (cross-spp transmission). Immune evasion (need better/updated vaccines). Resistance to treatment (concerns RNA viruses more).
Pandemic H1N1 (swine origin, Influenza A virus subtype H1N1 virus)
