Introduction to Viruses Flashcards
Describe the possible shapes of a virus
Icosahedral : 20 faces, each an equilateral triangle
Helical: Protein binds around DNA/RNA in a helical fashion
Complex: Neither helical or icosahedral
What are obligate intracellular pathogens?
Can only replicate inside a host cell
Viruses are these
What can virus families be classified according to?
Virion shape / Symmetry
Presence or absence of envelope
Genome structure
Mode of replication
Define virion
The complete, infective form of a virus, outside its host cell, with a core RNA and a capsid
What encapsulates the nucleic acid of a virus?
A protein capsid
What surrounds the protein capsid?
A lipid envelope containing spike projections
What are the stages of virus replication?
Attachment Uncoating Replication of genomic nucleic acid Protein synthesis Virion assembly (insertion of virus proteins into a membrane) Budding and release
What are the methods of viral transmission?
Blood bourne Sexual Vertical Faecal - oral Droplet Airborne Close contact Vector-borne (indirect transmission of an infectious agent - occurs when a vector bites or touches a person Zoonotic ( a disease that normally exists in animals but can infect humans)
What might the coinfection of human and animal or bird strains in one organism lead to?
Recombination and generation of a new strain
What are the syndromes associated with viral infections?
Respiratory Neurological Gastroenteritis Hepatitis Skin infections Eye infections Congenital abnormalities Arthralgia - infection of a joint Lymphadenopathy (disease affecting the lymph nodes)
What are the consequences of viral infection?
No, short or long lasting immunity
Chronic infection
Latent infection (lysogenic part of the cell cycle - lies dormant)
Transformation - long term infection with altered cellular gene expression
Describe the status of the viral genome during latency
Retained in host cell - expression is restricted (produces few antigen and no viral particles are produced)
What can does reactivation cause?
May or may not cause disease
When is reactivation most likely to occur?
In the immunocompromisd - also where it is most severe
How can some viral infections lead to cancer?
Modulation of cel cycle control - driving cell proliferation
Modulation of apoptosis - preventing programmed cell death
Reactive oxygen species mediated damage - infections can cause persistant inflammatory processes which lead to cancer via reactive oxygen species
What are the three aspects of a virus that you can detect?
The whole organism - microscopy, part of the organism (antigen, nucleic acid - PCR (extraction of genetic material followed by amplification of a specific region) -
or the immune response to a pathogen (used to determine a recent infection, prior infection or a response to vaccination)
What is common in all antiviral agents?
They are virustatic none are virucidal. This means they only inhibit the growth of the virus, stops the virus replicating
Why are their limited target proteins for antiviral drugs?
Virus utilises host cell enzymes in order to replicate
Give a reason why antiviral therapy is not used very commonly
Toxicity to the host cell is not uncommon
Give examples of when antiviral therapy may be used
Prophyaxis (prevents infection)
Pre-emptive therapy (when evidence of infection is detected but symptoms are not yet apparent)
Overt disease
Suppressive therapy - keeps viral replication below the rate that causes tissue damage in asymptomatic infected patient, common in long term immunodeficiency patients.
What are the possible methods of prevention of viral infections?
Immunisation (vaccination - active and passive)
Prophylactic treatment post exposure
Infection prevention and control measures (isolation of symptomatic patients, PPE, Safe disposal of sharps)
Screening - blood, tissue s and organs
Antenatal screening
When can viruses be eradicated?
No animal reservoir or ability to amplify in the environment
Clearly identifiable in diagnosis
No chronic state carrier (so you don’t miss those who are infected)
Efficient and practical intervention
Political and social support
