Virology IV Flashcards
Most DNA viruses contain dsDNA. What is an exception?
Parvovirus B19; adeno-associated virus (may be less important).
What is an example of an RNA virus with dsRNA?
rotavirus
What is a capsid? What are two kinds of capsids?
a capsid is a protective protein shell around a virus. usually made from repeating protein subunits. may be either helical or icosahedral. icosahedral capids are usually made of more than 1 protein
What is a viral envelope? What does it contain? What kinds of viruses have envelopes?
envelopes are made from cell membranes. contain a lipid bilayer interspersed with viral glycoproteins or other membrane proteins. Enveloped viruses tend to be less stable- usually NOT fecal/oral viruses (usually seen in direct contact viruses (blood, sex, insect/animal bite).
ourter surface proteins determine type-specificity.
What are the 4 stages of viral growth?
- adsorption
- eclipse (viral uncoating- 2-12 hrs). no infectious virus can be detected.
- synthetic phase: new virus particles are assembled- 12 hrs post infection
- latent: no extracellular viruses
eventually viruses will be detectable extracellularly. plateau level of viruses is eventually reached.
What is the difference between a receptor and a co-receptor?
time. typically, a virus will bind a receptor first (usually further from the plasma membrane), which causes a conformational change in the virus that makes it able to bind its co-receptor
In what two ways do viruses enter cells?
receptor-mediated endocytosis
direct membrane fusion
what happens during receptor-mediated endocytosis?
- ligand binds receptor
- membrane invagination with clathrin on the cytosolic side.
- pit pinches off
- vesicle fuses with early endosome
- early endosomes transported to late endosomes, which are acidic- ligands and receptors disossiate
- late endosomes fuse with lysosomes: most viruses escape before this stage (reoviruses are the only exception)
example of pH-dependent membrane fusion
hemagglutinin-neuraminidase protein of influenza virus
what happens during virus uncoating of the influenza virus?
M2 protein undergoes a conformational change at the low pH inside the endosome. this leads to activation of ion channel activity. protons enter the virus. interactions between the viral ribonucleoprotein (RNP) and the envelope protein M1 are disrupted. leads to virion disassembly.
What are some features of DNA viruses? exceptions? (ie. what do they bring with them and why)
tend to encode their own DNA polymerases
exceptions are parvoviruses and papillomaviruses (HPVs and parvovirus B19)
viruses without DNA pol must use cellular DNA pol- can only replicate in actively dividing cells.
What are the two groups of dsDNA viruses? what are some examples?
2 groups- those that replicate in the nucleus and those that replicate in the cytosol
cytomplasm example: poxviruses. need to encode factors to ensure transcription and replication of their genomes.
what is an example of a viruse with ssDNA genome? where does replication occur? what are the two classes of genes?
parvovirus
replication occurs in the nucleus
early genes are transcribed before DNA replication begins and products play a role in genome replication
late genes are transcribed after genome replication has started to form structural components of the virus
What is one important feature of dsRNA viral genomes? An example?
they tend to be segmented- each segment transcribed separately to produce individual monocistronic mRNAs (rotavirus)
What are the 2 groups of ss (+) RNA viruses? An example in each group?
- viruses with polycistronic mRNA. they produce polyprotein that must be proteolytically processed. example is the flaviviruses (west nile, dengue, etc.)
- complex transcription- 2 rounds of translation or subgenomic RNAs needed to make genomic RNA. Ex: rubella.
What are the 2 groups of ss (-) RNA viruses and examples?
- non-segmented: negative sense RNA transcribed by viral RNA pol. stop-start transcription yields monocistronic mRNAs. ex: measles, RSV (respiratory syncicial virus)
- segmended. influenza virus
Viral assembly and release: where? how?
assembly usually occurs at the site of DNA/RNA replication.
naked viruses are released from the host cell via a passive process (lysis), while enveloped viruses encode proteins that are inserted into cell membranes in patches. viral nucleocapsid is eveloped by a process of budding leading to viral release.
What two virus families cause more than half of all common colds? What kind of genome do they have? How are they spread?
rhinoviruses and coronaviruses
pos sense ssRNA
spread via sneezing (aerosol) and contaminated hands
What happens during infection with viruses for the common cold?
viral infection leads to damage to the integrity of the respiratory epithelial barrier
cells are killed and shed
bacteria colonized damaged epithelium
immune response happens (purulent fluid)
What virus most commonly causes pharyngitis and tonsillitis?
adenovirus
What viruses causes parotitis? what happens during this infection? How is it spread?
MUMPS infects the salivary glands
usually infects via resp. route and then spreads systemically. may enter the salivary glad tissue and the CNS. patients usually sow painful swelling of the parotid gland.
What virus is most often responsible for acute otitis media in kids?
RSV (resp. syncitial virus)
What is brionchiolitis? What virus causes it most frequently?
bronchiolitis: inflammation of the brionchioles that usually occurs before 2 yrs of age. epithelial cells that line the bronchioles necrose. can lead to viral spread into lung parenchyma and interstitial pneumonia.
often caused by RSV.
RSV: genome, transmission, diseases it causes, prevention
ssRNA, neg. sense
droplet transmission
kids infection, elderly infection, otitis media
prevention can involve IV admin of antiviral monoclonal antibody against viral F protein.
Influenza virus: genome, what happens
segmented neg. ssRNA
3 types of flu
viral damage to the resp. epithelium predisposes to secondary bacterial infection, which can be life-threatening.
influenza drugs
neuraminidase inhibitors (zanamavir and oseltamivir) M2 proton channel inhibition (amantadine and rimantadine_)
What are the differences between influenzas A, B, and C?
A- causes epidemics and pandemics. avian reservoirs
B- epidemics. no animal reservoirs
C- mild illness, no epidemics
human metapneumovirus: genome,
like RSV- neg sense ssRNA
infects most kids in US before age 5
may cause up to 15% of infant bonchiolits
adenoviruses: genome, illness
dsDNA virus
cause many acute resp. tract illnesses, esp. pharyngitis and tonsillitis
SARS- genome, viral family
pos ssRNA genome
coronovirus
bocavirus
ssDNA parvovirus. may cause bronchiolitis
8 viral causes of pneumonia
- RSV
- influenza
- human metapneumovirus (kids)
- adenovirus
- SARS and other coronoviruses
- Measles
7, CMV infection (immunosuppressed ppl) - Bocavirus (kids)
Measles: genome, unique features
neg ssRNA
paramyxovirus
relatively high mortality
almost all infected ppl develop the disease
immunity is lifelong and only single antigenic type of virus
very infectious
outcome worse in malnourished kids
How is measles spread? What happens once in body? What are clinical features of measles?
spread by inhalation of particles that replicate in the lymphoid tissue and then spread through the blod
clinical features: resp. illness, conjunctivitis (3Cs: cough, cold, conjunctivitis), Koplik’s spots (bright red leasions with central whit dot in buccal mucosa), and maculopapular rash that reflects T cell response.
Measles: complications and vaccination
complication: postinfectious encephalitis due to immune response against myelin
vaccine is live-attenuated
Rubella: virus type/genome, transmission, complications
pos ssRNA virus (togavirus)
transmitted by droplet infection
causes multisystem disease
used to cause deafness in congenitally infected ppl and eye and heart lesions.
