Virology Flashcards
What is a virus?
- collection of genetic information inside a protective protein coat
- obligate intracellular pathogen -> needs host cell machinery to replicate;
cannot divide/replicate on their own
What can viruses be repurposed for?
- Therapeutics (e.g., gene therapy)
- Research tools
What are the common vaccines and the way they’re transmitted?
- HIV-1 -> blood, sexual
- hepatitis C-> blood, sexual
- herpes simplex virus-1, 2-> skin contact/sexual
What are the rare vaccines and the way they’re transmitted?
- hantavirus -> aerosol
- lassa fever -> aerosol
- west nile -> mosquitoes
What are the purposes of the virus structure?
- To protect the viral genome.
- To detect the appropriate host cell for infection.
- To deliver the genome to the correct subcellular site for replication.
- To carry enzymatic activities necessary for initiating viral infection.
What are the characteristics of a non-envoloped virus structure?
- a genome surrounded by protein shell (capsid)
- stable to environment
- ex: poliovirus, adenovirus, FMDV
What are the characteristics of an envoloped virus structure?
- have a capsid (nucleocapsid) surrounded by a lipid bilayer that has viral proteins protruding from it
- sensitive to environment
- produced by budding
- ex: HIV-1, VZV (chicken pox), influenza
What are the 2 types of capsid symmetry?
icosahedral & helical
What are the characteristics of icosahedral symmetry?
- not stable in environment
- 20 triangular faces
12 vertices - 2, 3 and 5-fold axes
of rotational symmetry.
formed from subunits - “Closed” structure
Why are subunits important?
- Necessity: genome size limits amount of available coding sequence.
- Self assembly: subunits can come together spontaneously.
- Fidelity: smaller chances for mutations within small genes.
- Economy: misfolded proteins cannot be used to form structure (less waste).
- Complexity: larger number of subunits results in more contacts (stability).
What are the characteristics of helical symmetry?
- Rodlike or filamentous structures
- Generally enveloped viruses
- “Open” conformation (adjustable size)
What was the criteria used for viruses?
- structure
- type of genome: segmented vs non-segmented
- disease
- host
- containment level
- range: tropism - what cell type does the virus affect?
How can you classify a new virus?
- high thorughout nucleic acid sequencing -> cultured virus; samples from infected individuals
- PCR -> highly conserved proteins
- serology -> serum from infected individuals; neutralization
- electron microscopy -> identify shape, size, symmetry, enveloped vs non-enveloped
How can you classify an existing virus?
- genetic material -> RNA or DNA
- capsid symmetry -> icosahedral, helical, complex
What is the ICTV classification?
- based on biological classification system
- order: general genome organization
- family: genome organization/gene arrangement
- genus: genome organization/size & sequence homologies
- species: ecological niche
- serotype: antigens
- strain: group in specific geopgraphy
What is the genetic content for RNA viruses?
- usually single stranded
- plus -> icosahedral capsids
- minus -> ALL helical capsids; some non-segmented & segented genomes; must be transcribed first!!
- double
What is the genetic content for DNA viruses?
- usually double stranded
- exceptions -> parvoviruses & hepadnavirus (HepB)
- linear or circular
- have icosahedral symmetry
What are the characteristics of category A CDC select agents?
- easily disseminated or transmitted person-to-person.
- cause high mortality, with potential for major public health impac -> no way of treating
- might cause public panic and social disruption.
- require special action for public health preparedness.
What are the characteristics of category B CDC select agents?
- moderately easy to disseminate
- cause moderate morbidity and low mortality
- require specific enhancements of CDC’s diagnostic capacity and enhanced disease surveillance
What are the characteristics of category C CDC select agents?
- readily available
- easy to produce and disseminate.
- potential for high morbidity and mortality and major health impact
What are the initial stages of infection?
- reservoir
- transmission
- site of infection
- host range
- productive infection
What are the host responses to a viral infection?
- Natural barriers ->ucous membranes, skin
- Innate immunity -> cells, secreted factors
- Adaptive immunity -> cellular immunity, humoral immunity
What are the 3 patterns of infection & disease?
- Acute infection followed by viral clearance
- Acute infection followed by latent infection
- Acute infection followed by chronic infection
What are examples of acute infections followed by viral clearance?
- Colds and respiratory infections -> rhinoviruses, coronaviruses, mild disease (fever, rhinitis)
- Influenza -> 3 major types (A, B, C), moderate disease (fever, rhinitis, bronchiolitis, pneumonia)
- Variola (smallpox) -> 2 forms of disease (major, minor), severe disease (fever, skin lesions, death)
What are the characteristics of acute infections followed by viral clearance?
- either localized or disseminated
- ultimately eradicated
What problems can arise with an acute infection followed by a viral clearance?
- infection of “non-target” tissue
- not primary tissue of replication
- “dead end” or non-replicating infection
- causes atypical disease
- examples: polio, rubella
What are the characteristics of an acute infection followed by latent infection?
- initial infection and apparent clearance
- viral genomes maintained in specific tissues, cell types
- reactivation by physiological responses to external stimuli
- ex: herpes simplex 1
What are the characteristics of an acute infection followed by chronic infection?
- initial infection
- partial clearance
- persistent infection and production of virus
- ex: HIV & tumors
What are the potential consequences of a chronic infection?
tumors (cancer) & autoimmune diseases
How do viruses spread through a population?
- Endemic: continuous transmission within a population
- Epidemic: peaks of disease above baseline or expected rate
- Pandemic: worldwide epidemic
