Introduction to Viruses Flashcards
Describe the possible shapes of a virus
Icosahedral : 20 faces, equilateral triangle
Helical: Protein binds around DNA/RNA in helical fashion
Complex: Neither helical or icosahedral
What are obligate intracellular pathogens?
only replicate inside host cell
Ex. Viruses
What can virus families be classified according to?
Virion shape / Symmetry
Presence or absence of envelope
Genome structure
Mode of replication
Define virion
Complete, infective form of virus, outside host cell, core RNA and capsid
What encapsulates the nucleic acid of a virus?
protein capsid
What surrounds the protein capsid?
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 infectious agent - occurs when a vector bites or touches a person
Zoonotic (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 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 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 restricted (produces few antigen and no viral particles)
What can reactivation cause?
May or may not cause disease
When is reactivation most likely to occur?
immunocompromisd - most severe
How can some viral infections lead to cancer?
Modulation of cell cycle control - driving cell proliferation
Modulation of apoptosis
Persistent inflammatory processes lead to cancer via reactive oxygen species
What are the three aspects of a virus that you can detect?
Whole organism - microscopy
Antigen, nucleic acid - PCR
Immune response to pathogen (recent/prior infection or response to vaccination)
What is common in all antiviral agents?
Virustatic
None are virucidal
Only inhibit virus growth and replication
Why are their limited target proteins for antiviral drugs?
Virus uses host cell enzymes to replicate
Give a reason why antiviral therapy is not used very commonly
Toxicity to host cell
Give examples of when antiviral therapy may be used
Prophylaxis (prevents infection)
Pre-emptive therapy (evidence of but no symptoms)
Overt disease
Suppressive therapy
Suppressive therapy (keeps viral replication below 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)
Prophylaxis after exposure
Screening - blood, tissues and organs
Antenatal screening
Infection prevention and control measures (isolation of symptomatic patients, PPE, Safe disposal of sharps)
When can viruses be eradicated?
No animal reservoir or ability to amplify in environment
Clearly identifiable in diagnosis
No chronic state carrier (don’t miss those who are infected)
Efficient and practical intervention
Political and social support
