Virology Flashcards
what are viruses?
Obligate parasites that can function only after they replicate in a cell
Viruses depend on their host to survive because:
If viruses are too successful and quickly kill their hosts, they immediately eliminate themselves too e.g. omicron
If viruses are too passive and the host can stop their growth, then they also eliminate themselves
Name 3 different phases withing a virus (LEM)
Eclipse phase, here there are no viral particles yet
Maturation phase, here only cell-associated viruses are present
Latent phase, the release of the virus
The genetic material is surrounded by:
a protein capsid (helical or icosahedral)
What is the function of a capsid?
Protecting nucleic acids from chemical, physical and enzymatic damage
Why do viruses only use a limited number of designs?
Because it requires less genetic material because it repeats
How many subunits does a isohedrical capsid have?
60
Metastability =?
the ability of a non-equilibrium state to hold for a long time
Whats the difference between naked and eveloped viruses?
Naked viruses are composed of only the nucleocapsid and enveloped viruses have a layer of plasma membrane taken from the host cell that surrounds the nucelocapsid
Whats the function of spikes?
They add to the attachment of the virus to a host cell membrane
Host range =?
it defines the number of host species used by a pathogen
Whats the difference between specialists and generalists?
Specialists infect a limited amount of hosts and generalists infect a large range of hosts
Whats the difference between specialists and generalists?
Specialists infect a limited amount of hosts and generalists infect a large range of hosts
Tissue tropism =?
The different cell types that can be infected by the virus
a resistant cell has:…
no entry receptor, the the cell may or may not be able to support the viral replication
A susceptible cell has…
a functional receptor for a given virus, so the cell may or may not support viral replication
A permissive cell can…
replicate the virus, but may or may not be susceptible
A susceptible and permissive cell can…
take up a virus particle and replicate it
Primary cells…
are prepared directly from an animal or human tissue (can be subcultered)
Semi-coninuous diploid cells…
are derived from human fetal tissue
Continuous cells…
are derived from tumors of human or animal tissue
Name 4 quantification methods (pfvt)
Plaque assay, fluorescent focus assay, virus in cell culture and TCID50
Multiplicity of infection (MOI) = ?
the number of indectious particles added per cells
Name 6 physical measurements of virus particles
Heamagglutination assay, haemagglutination inhibiton assay, EM, ELISA, flowcytometry, and antigen rapid test
Name the 6 steps of the viral life cycle:
attachment, penetration, uncoating, biosynthesism assembly and release
What happens during attachment?
The virus adheres to the cell surface by electrostatics and attaches to a receptor molecule on the cell surface
What happens during penetration?
The virus is endocytosed or fuses with the host cell membrane
What happens during uncoating?
The capsid is degraded either in the cytoplasm or in the endocytic vesicle
Uncoating is triggered by the host cell enzymes
Name 4 modes of nuclear entry:
through pores, docking at pores, pushing with motor tubules or by disrupting the nuclear membrane
How to T4 bacteriophages target the bacteria?
By penetrating the cell with a needle and injecting their particles inside the cell
Name 3 modes of assembly:
self-assembly, with the help of scaffolding proteins or by precursor proteins for proteolytic cleavage
Name 2 modes of release
by budding of the plasma membrane (enveloped viruses) or by cell lysis
What happens during maturation?
Virus become infectious by proteolytic modifications to the capsid or envelope
Name 2 important events that happen after infection:
procution of virus structural proteins and enzymes, and replication of the viral genome
Why do all viral genomes must make mRNA?
So that the host ribosomes can read the viral genome
Whats the difference between + strand mRNA and - strand mRNA
+ strand has the same polarity as mRNA and - strand is complementary to the + strand and can not be translated
Where does the poxyvirus replicate?
In the cytoplasm and brings its own DNA and RNA enzymes
What is needed for DNA synthesis?
DdDp and primers
Why is RNA more prone to mutations compared to DNA
Because RdRp has no proofreading comared to DdDp
Antigenic drift =?
minor point mutations where the immune system no longer recognizes hemagglutinin and HA/NA proteins
Antigenic shift=?
A sudden and major change in surface antigens when 2 different strains inject the same cell at the same time and undergo genetic reassortent
Why is antigenic shift so dangerous?
Because the change is so drastic that it can cause pandemics or outbreaks because the virus is so new and barely anyone has any prior immunity to it
Viral virulence =…
The capacity of a virus to cause disease in a host
Clinical signs=…
Attributes of infection that are objectively measured e.g. rash, body temperature
Clinical symptoms=…
Attributes of infection that are subjectively assessed e.g. pain or soreness
Incubation period =…
The initial period before symptoms of disease are obvious
When can a virus enter an entire organism?
When there is sufficient virus particles present, cells at the primary site of infection must be accessible, susceptible and permissive, and the host immune system must be absent
Name 4 ways a virus can be present/spread in the host
- . Localized, so the virus stays at the primary site
- Dissemination, it spreads from the primary site
- Viremia, it is present in the blood
- Systemic, it spreads to multiple susceptible organs
Acute infection…
Sudden onset/short time infection
Subclinical infection…
Same as acute but there are no signs of symptoms present
Persistent infections…
Infect a few cells and produce low level of progeny
Chronic infections..
more active and have a larger yield
Latent infections…
Always start acute/subclinical and you have flare-ups of the disease
Slowly progressive infections…
Takes many years to manifest, virus particles are still produced
Virus-induced tumors…
Viruses induce transformation of genetic materual e.g. HPV
How can a virus leave the host body?
Through following the route of entry, sneezing, nasal secretions, feces, sperm etc.
Horizontal transmission:
between members of the same species, or different species (zoonotic), or via intermediate species that carry the virus
Vertical transmission
the transfer of infection between mother and child
Iatrogenic
by the activity of a health care worker e.g. injection
Nosocomial
while in the hospital or health care facility
Germline transmission
proviral DNA is transmitted as part of the genome
R-0 =….
number of secondary infections that can arise in a population of susceptible hosts from a single infected individual
