Respiratory Viruses Flashcards
what is the virus family, genome, and virion of influenza?
- orthomyxoviridae
- segmented (-)ssRNA
- enveloped
what is the virus family, genome, and virion of adenovirus?
- adenoviridae
- dsDNA
- non-enveloped
what is the virus family, genome, and virion of rhinovirus?
- picornavirus(childhood viral section)
- (+)ssRNA
- non-enveloped
out of the 3 types of influenza (A, B, C) which is the most common and associated with greatest concerns?
type A influenza
what proteins are associated with type A influenza?
- HA: hemagglutinin, cell attachment
- NA: neuraminidase, viral budding and release
- M1: matrix
- M2: ion channel
- PB1, PB2, PA: transcription complex
which of the type A influenza proteins is often the target of antivirals?
NA
which type A influenza protein is the major determinant for human to human transmission?
HA
what type of reservoir does type influenza have?
animal
how is type A influenza viral replication initiated?
- attachment brings cell and virus membranes into close proximity
- conformational change triggered after cell attachment by pH change in endosome
- causes membrane fusion
- model for all enveloped viruses
where does transcription and replication occur for type A influenza?
- nucleus (EXCEPTION)
- protected genome (RNP core) escapes nucleus and buds from cell surface
- NA critical to budding (cleaves connections to free virus so go to extracellular space)
how is influenza transmitted?
-aerosol, large and small droplets
*infectivity greatest for particles <10 microns
**ID50 as low as 0.3-6, 50% egg infectious doses (IED50)
=every 10 particles for 1 egg infectious dose so 0.3 =~3 particles so why it is possible to be enough to cause illness
what is the incubation time for influenza?
1-4 days: contagious day before symptom onset to 5 days later
T/F: infection from influenza causes the innate immune response to come into play early
true
describe seasonal (interpandemic) flu
- fever, malaise, nonproductive cough, sore throat
- lasts 3-7 days after symptoms develop
what are some complications from seasonal flu?
- viral pneumonia
- bacterial pneumonia
- reye syndrome (type B + aspirin)
- otitis media
how is influenza virus prevented?
- attenuated live vaccine:
- virus mutations require new vaccine development every year- antigenic shift
- long lead time
- usually contains an H3N2, H1N1 and Type B strain
- type A strain generated thru reassortment via coinfection with PR8 strain
how is influenza treated?
- antiviral treatment:
- amantidine: inhibits acidification of endosome so HA has conformational change
- blocks entry of ions, and inhibits M2 activity (described above)
- development of resistance common
- zanamivir or oseltamivir (tamiflu):
- blocks release of budding virions
- development of resistance is not common
-supportive care
what are the 4 major influenza pandemics?
- 1918 spanish flu
- 1957 asian flu
- 1968 hong kong flu
- 2009-2010 H1N1
what strains of influenza are pandemics thought to arise from?
avian
describe avian influenza (H5N1)
- highly pathogenic avian influenza: H5 or H7 strains
- lethal in >75% of 6-8 week old susceptible chicks
- HPAI strains have multi-basic residues at HA cleavage site allowing replication thru out the body
- skin lesions, necrotic & swollen combs, systemic infection
- low pathogenic avian influenza: asymptomatic to slight respiratory infection, no lesions
- H5 and H7 strains can mutate to HPAI strains
how did H5N1 become passable between animals through airborne droplets?
the dutch did an experiment with ferrets and after 10 generations virus was capable of airborne transmission between animals
how is adenovirus characterized?
- by their serotype
- diff serotypes associated with different diseases
- Ad 2 & 5 most frequently studied
what are the proteins associated with adenovirus?
fiber: cell attachment
penton base: cell entry
hexon: capsid
how does adenovirus enter into a host?
- via coxsackie-adenovirus receptor (CAR)
- pH triggered capsid disassembly
- moves to nucleus
how is the adenovirus gene expression in 3 phases?
- immediate-early: E1A portion of genome- 2 transcriptional regulators (cell & virus), necessary to reach early stage
- Early: 5 genome sections - E1B, E2. E3, E4 and L1, DNA replication & post transcriptional events
- Late take over of cellular mRNA
where does adenovirus replication occur?
dsDNA so replication in nucleus
how does adenovirus exit the host cell?
weakly lytic because doesn’t have proteins lysing membrane so need cell to die and rupture
describe the genome replication process of adenovirus
- initiated on either end, identical end sequences
- replication in 5’-3’ direction, one strand displaced
- displaced strand circulizes to allow template copy to be made
- primed by the protein pTP, unusual priming strategy
when does DNA replication occur in the mitotic cycle for adenovirus?
s phase, not all cells are actively replicating
how does DNA replication occur specifically with the genome sections?
- E1A inactivates pRb leading to s phase gene expression
- E1B inactivates p53 leading to s phase and preventing apopotosis
- similar to oncogenic processes
what does the E3 genomic component of adenovirus do?
-produces proteins important to host immune evasion
**what can adenovirus block?
- MHC class I expression reducing CTL cell killing
- TNF induced apoptosis
- IFN-alpha and IFN-beta action keeping protein translation active
what kind of clinical diseases does adenovirus cause?
- resp infections very common
- typical symptoms of common cold
- acute resp disease (ARD): severe pneumonia seen in miliary; serotypes 4&7; vaccine for military
T/F: adenovirus is a frequently used vector
T
what virus is the frequent cause of mild upper resp infections?
rhinovirus
does rhinovirus have many serotypes and therefore large antigenic diversity?
yes over 100 serotypes
what is the only known reservoir for rhinovirus?
humans
how does rhinovirus enter the host?
attaches to intercellular adhesion molecule 1 or the very low density lipoprotein (VLDL) receptor
DIRECT INJECTION
what is the incubation period for rhinovirus?
1-4 days
how long is virus shedding detectable for rhinovirus?
2-3 days but sometimes detected up to 3 weeks afterwards
what are the symptoms of rhinovirus?
red nose, blood vessel dilation, nasal discharge that become mucopurulent (neutrophils), epithelial damage likely due to immune response
how is rhinovirus prevented?
no vaccines b/c too many serotypes and no antivirials b/c resistant mutants
