Introduction to Virology Flashcards
viruses are a ____ complex that infect cells
nucleoprotein
viruses are metabolically
inert
which is false about viruses
1. DNA viruses assemble in cytoplasm
2. mostly highly species specific
3. are metabolically inert
4. virion is the whole spreadable particle
1- nucleus
what is the nucleocapsid
genome + capsid
capsomere functions
helps define shape of capsid
viral envelopes are
1. host
2. virus
3. both host and virus
4. made from capsomeres
1
Viruses with similar structural, henomic, and replication properties are grouped into __________ (ex- suffix_________)
families
-viridae
families are sudivided into ____
genera
virus subtypes are based on
nucleotide sequence and antigenic reactivities
viral capsid forms include
helical
icosahedral
complex
basic viral envelope forms include
icosahedral nonenveloped
icosahedral enveloped
the viral envelope is involved in (4)
attachment, entry, assembly, release
envelope proteins are ___, lipids are ______
viral
host
T or F: if membrane envelope is destroyed, the virus infects all cells in its proximity by direct benetration
F- virus becomes noninfectious
3 forms of adsorption/ attachment
direct penetration
fusion
endocytosis
describe direct penetration with viral attachment
Usually nonenveloped virus penetrating host cell through receptors on side of plasma membrane = release virus directly into host cell
Capsid is left behind
describe fusion with viral attachment
only with enveloped viruses. Viral glycoproteins bind receptors of host cell = fuse envelope with membrane and releases viral capsid inside host cell
describe endocytosis with viral attachment
Host cell engulfs virus, capsid, and envelope all together- host cell mem, envelope, and capsid all disintegrate inside host cell
describe uncoating
removing all or part of viral capsid
viral genome is accessible to host cell’s transcription and translation machinery
DNA viruses replicate in
host cell nucleus mediated by viral enzymes
T or F: viruses come with some of their own enzymes to reproduce within host cell
T
T or F: all portions of DNA virus are replicated in host cell cytoplasm
F- only DNA in nucleus, rest are in cytoplasm
which virus is the exception to the DNA virus replication rule
poxvirus- DNA but synthesize in cytoplasm
____ type RNA acts as mRNA
+
viral proteins with RNA viruses are made in
cytoplasm
T or F: naked RNA nucleic acid is infectious
T
neg sense RNA must first ___________________ before it can replicate
make a + sense RNA/ mRNA
viral capsomers _______ assemble into crystal like arrays
self
describe the 3 points of viral assembly
Replication of viral genome and synthesis of proteins are complete
Viral capsomers self assemble into crystal like arrays
Newly formed capsid is filled with viral nucleic acid and buds out
enveloped viruses are typically released by
budding
is budding always lethal to the host cell?
not always, sometimes
how are nonenveloped virions released
when the cell lysis
After encountering a host cell, the virus must (3)
Enter the cells
Undergo a period of primary replication
Spread to its final target tissue- infect and successfully replicate in a susceptible population of host cells
3 types of viral infections
lytic
latent
chronic
describe a lytic infection
Multiple rounds of replication results in death of the host cell (virus factory)
Polio, influenza
describe a latent infection
No immediate production of progeny virus
Viral nucleic acid carried as extrachromosomal element or an integrated sequence in the host cell DNA
in latent infections, the viral nucleic acid is carried as an ___________ or __________
extrachromosomal element
integrated sequence in host cell DNA
describe a chronic viral infection
Virus particles continue to shed after the period of acute illness has passed
slow release of virus particles without death of host cell
4 types of virus host cell interaction
lytic
cell transformation
latent/ occult
cell fusion to form multinucleated cells
respiratory route of transmission involves
Aerosol droplets, nasal secretions, or saliva via coughing or sneezing
common cold is spread by
aerosols and fomites
GI route of viral infection is from
viral shed in feces- contaminate food or water - ingested by susceptible individual
stool tainted hands, poor hygeine
transcutaneous route of infection involves
Direct inoculation via insect, animal bites or mech devices like needles
west nile is spread
transcutaneously
why are humans a dead end for west nile
do not develop high levels of virus in bloodstream = can’t pass virus on to other biting mosquitos
iatrogenic transcutaneous infections are induced by
medical or diagnostic procedures- contaminated blood products, infected donor material, purposeful as vaccination, etc
sexual transmission of viruses may see the virus spread to
to other parts of the body or remain near the site of entry
horizontal sexual transmission is between
between members of a susceptible host population
vertical sexual transmission is
infection of fetus in utero through virus carried in germ line or infecting the placenta or in the birth canal
T or F: viruses may stay at the same site or spread to other area to produce disease
T
which has no role in primary response or acute viral infections
1. complement
2. cell mediated immunity
3. antibody response
4. 3+4
3
antibody response is very important in ______________. neutralizing antibodies reduce effectiveness by _________, _____, _______
preventing reinfections
inhibiting attachment, penetration, or uncoating of virus
viruses can trigger the activation of the ___ and _______ pathways of complement
alternate
classic
virus activated complement enhances _________ = _____________
phagocytosis of viruses = lysis of enveloped virus or virus infected cells
what happens in cell mediated immunity
infected cells are susceptible to the action of lymphocytes that recognize viral antigens on their surface = can be lysed
CPE applies to
virus induced cellular changes that are visible by light microscope
the most effective way to visualize viral changes to cells is by
staining cells with chromatic dyes
what is the basic and acidic dye in CPE
basic = hematoxylin
acidic = eosin
direct detection fluorescent antigen is used for
viruses that create lesions
how to prep sample for direct fluorescent antigen observation under UV microscope
Vigorous scraping of lesion base is essential- remove scab before sampling
dierct detection fluorescent antigen uses _______________________ for detection
Uses HSV antigen specific murine MAbs (fluorescein labeled) for detection
Direct detection fluorescent antigen is observed under
UV microscope
pros of viral culture
Can differentiate between viable and non-viable viral particles
Able to detect unknown viral etiologies
Inexpensive compared to PCR
cons of viral culture
Relatively slow
Does not support growth for all types of viruses
Toxins can resemble cytopathic effects = false +
Contamination due to bacteria, fungus and mycoplasma reduce the sensitivity of viral detection
Endogenous virus from cells can be mistaken as the infectious agent
_________: fourfold or greater increase in antibody titre to spec viral agent in acute and convalescent sera (3-4wks later)
serology
IgM antibody is a marker of
current/ acute rxn
IgG is a marker of
past infection in the last 3-4weeks
molecular studies are the
detection of even single copies of virus genome in tissues or cells from body fluids
molecular studies utilize _____ which may be visualized by ____ or _________
PCR
gel electrophoresis
real time by computer
pros of viral amplification
Can detect v low number of viruses
Rapid
High throughput
Multiplexed assays
cons of viral replication
Contamination due to high conc of amplicons
Detection of dead organisms
False + and false - results
Expensive
Special training
