Chapter 6 Flashcards
Viruses
a non-living pathogen, submicroscopic (very tiny), infectious agents
Virology
Study of viruses
Bacteriophages
viruses that infect bacteria
Animal viruses
Viruses that attack animals (aka us)
Virion
Single virus particle
Capsid
□ Protein shell that protects the genome and accounts for virions mass
Helical capsid
look like hollow tubes
Icosahedral Capsid
looks like 3d polygons
Complex Capsid
Deviations from icosahedral and helical capids
Enveloped viruses
have a lipid-based envelope that surrounds the capsid
Naked viruses
lack an envelope
Spikes
protrude from the viral capsid or envelope, help viruses attach and gain entry to host cells
Influenza A spikes
Hemagglutinin (HA)
Neuraminidase (NA)
How many genes does a virus have?
only about 300
Viral Genomes can be
RNA + DNA
Single or double stranded
Single or segmented sections
Circular or linear
Attenuated strains
genetic changes that limit infectivity
Antigenic shift
leads to increased infectivity or expanded host range
Antigenic drift
RNA genome mutates frequently causing major changes to HA and NA spikes
Host range
collection of species that viruses can infect
Tropism
the turning of all or part of an organism in a particular direction in response to external stimulus
Viral Tropism
ability of a particular virus to infect a particular cell or host species
Lytic replication pathway: Steps
Attachment: binds to host cell
Penetration: injects genetic material to host
Replication: phage commandeers host cell factors to transcribe and translate viral genes
Assembly: ): Genome packed into capsid and phage structures assembled
Release: Bacterial cell lyses and new phages are released
Lytic replication pathway
infect the host bacterial cell, build new virions, then kill the host
Lysogenic replication pathway
infect bacterial cell, phage genome is incorporated in to host cell genome become prophage
Lysogenic replication pathway: Steps
Attachment
Penetration
Phage genome is incorporated into the host cell genome forming a prophage
As the cell divides, it copies the prophage
Host cell is stressed, the prophage may excise itself from the host genome
Phage enters the lytic replication pathway
Animal virus replication
Attachment
Penetration
Uncoating
Replication
Assembly
Release
Acute infections
infect a host cell and new virions are made
Persistent infection
viruses with replication strategies that allow them to avoid the immune system
Persistent chronic infection
when virus enters but stays dormant enough to not trigger an immune response
Persistent latent infection
has an immediate response, body tries to clear it but some stay in a dormant state until later
Oncogenic viruses
viruses that cause cancer
What is needed to grow virus samples?
host tissue, like rats for animal virus growth
Why are diagnostic tests necessary?
to make sure products and tissues are safe
Specificity
means that the test only detects the virus of interest
Sensitivity
means the test detects very low levels of the target
Agglutination tests
Purified antibodies linked to tiny latex beads
ELISA
Can detect either antigens or antibodies in a sample
Antiviral drug classification
Five main groups of antivirals based of what stage of the virus they attack
Post-exposure prophylaxis (PEP)
Mixture of antibodies that prevent viruses from binding and entering host cells
Tamiflu + Relenza
Prevents influenza A and B from budding off cell surface
Prions
infectious proteins, have no genetic material thus can’t replicate. Cause transmissible spongiform encephalopathies (TSEs)
Creuzfeldt-Jakob disease (CJD)
Rare, degenerative and fatal brain disorder
Creuzfeldt-Jakob disease (CJD): Categories
Sporadic: appears even if patient has no known signs
Hereditary: patient has a family history of disease
Acquired: Usually done by certain procedures if exposed to brain and tissue
Gerstmann-Straussler-Schienker
An extremely rare hereditary disease, the gene found in just a few families around the world
Kuru
considered an acquired prion disease
