Viral respiratory infections Flashcards
___ is a +ve sense, non-enveloped ssRNA virus (belongs to Picornavirus family) that mainly causes the common cold
Rhinovirus
Describe the replication cycle of rhinovirus
Basically the same as any other non-enveloped rna virus. Since its +ve sense, no need to bring its own rna polymerase, and two important things are: Rhinovirus exits the cell via lysis (makes sense coz its naked so it doesn’t need an envelope) which causes an inflammatory response and has an icosahedral capsid which is important for vaccine design/lack thereof
Where in the URT does Rhinovirus replicate?
Which component of the immune system is involved in fighting Rhinovirus infection?
In nasal epithelium
Only innate immunity involved
**also know that viral titers peak within 2 days and are gone by day 5 so I guess that’s when you’re symptomatic, and symptoms happen a day after inoculation**
What are the groups of Rhinovirus and which one is the most clinically important?
Groups A, B and C
**Group A most clinically important**
___ is a -ve sense, enveloped ssRNA virus that, like Rhinovirus, primarily causes URI but can also cause viral pneumonia in severe cases
Influenza virus
**Recall that the Influenza virus belongs to the Orthomyxovirus family and has 8 segments (the O in BOAR)**
**remember also that this family replicates in the NUCLEUS unlike the other rna viruses**
Describe the structure of the flu virus. Which 2 proteins are on the viral envelope that are crucial for its function? ___ is also an envelope protein-channel that mediates viral uncoating
Envelope is studded with various proteins including hemagglutinin, and neuraminidase (HA and NA). Envelope also has the M2 protein which is a channel that mediates viral uncoating
How is flu transmitted?
Describe the influenza vius replication cycle
HA binds to sialic acid which allows for endocytosis of viral capsid
Viral genome goes to nucleus for transcription, m-rna exported out to cytoplasm for translation and proteins meet and assemble at plasma membrane.
Resulting virion exits via budding, unlike Rhinovirus which leaves by lysis
There are currently 3 drugs used to treat flu. Name them (hint: Amanda, Tammie and a Balo-rena)
Amantadine (Symmetrel) blocks M2 (so it blocks uncoating mediated by acidification of the endosome) – all strains currently resistant to this
Oseltamivir (Tamiflu) blocks neuraminidase (which cleaves sialic acid on the membrane from which the virion is budding so it can actually leave the cell)
Baloxavir/Xofluza – blocks the virus’ cap snatching process (so basically the virus steals a 5’ cap from the host m-rna and places it on its own m-rna so the drug blocks the virus’ cap-dependent endonuclease)
Explain the difference between antigenic drift and antigenic shift
Antigenic drift: point mutations in the viral genome that results in variations in HA and NA proteins – so that’s why we need a new vaccine every year
Antigenic shift: when segments are shared (and recombine) between different spp of influenza virus
Describe the current flu vaccines that are out there
There’s a standard inactivated vaccine from various strains, then a live attenuated vaccine made from recombinant HA and NA proteins from same genomic backbone
Contrast the 2 theories behind a universal flu vaccine
Headless HA theory: you remove the head of the HA protein which is highly variable and you make antibodies against the stalk, which doesn’t change as much
Stalk - diff head antibodies: you make antibodies to one stalk type you also boost with antibodies against same stalk but different HA heads
Describe the characterstics of parainfluenza virus
-ve sense ssRNA virus; member of the Paramyxovirus family; enveloped
What is a key difference betweent the replication cycles of flu and paraflu?
Parainfluenza most commonly causes __ and __
Difference between Paraflu and flu is that this has a Fusion surface protein that allows it to fuse with the plasma membrane and release its genome that way without the endosome acidification that’s required by flu
Parainfluenza most commonly causes Croup and bronciolitis
Describe the replication cycle of parainfluenza virus
Effectively the same as other rna viruses
*virus fuses with membrane via the F protein at NEUTRAL pH, and replication takes place in the CYTOPLASM, unlike flu*
How is parainfluenza virus transmitted?
Where does the virus replicate (hint: this is why infants are acutely susceptible to infection)
PIV is transmitted via droplet transmission/person-person contact
It replicates in ciliated epithelial cells, and infants are more suscpetible b/c they don’t make enough mucus/layer is more fragile and their cilia are less developed
Describe the replication cycles of RSV and HMV
Why is RSV called RSV?
Both the same as other rna viruses: replicate in the cytoplasm. Difference: binds to cells using the G protein but fuses to membrane with F protein
Basically, cells neighboring the virally infected cell will also have the virus’ receptor and the fusion protein so somehow that can causes the cells to stick together and form syncytia, which are generally weaker, burst more easily and can lead to a more serious inflammatory response/disease
Describe the characteristics and replication cycle of Adenovirus
F fibers on the virus dissociate from its surface which allows for new proteins to bind inside and traffic the viral genome to replicate in the nucleus
**its a ds dna virus, non-enveloped (the A in DNA viruses are HHAPPPPy)
A 2 year old child, who began attending day care shortly after the New Year holiday, comes home with a runny nose but is otherwise active and well. Two days later, in the middle of the night, the child wakes up with a sharp “barking” cough, fever, and is very irritable.
What is the syndrome and the virus that causes it?
Acute Laryngotracheobronchilitis (Croup) caused by Parainfluenza spp
**note that the infection has moved lower down the respiratory tract from larynx to main bronchi region**
How do you Dx croup?
At what point in the year does parainfluenza infection peak?
Seasonality: mainly winter time and is gone by summer
Dx: need to see steeple sign on neck x-ray (aka tracheal narrowing)
others:
nasal wash for viral culture, immunofluorescence, PCR
serological test, IgG and IgM
A 2 month old infant, born in October, experiences worsening fevers, cough with profuse nasal secretions, and some mild wheezes. After a week the infant has worsening symptoms and is hospitalized because oxygenation is worse.
What is the syndrome and which virus causes it?
Syndrome: Bronchiolitis caused by Respiratory Syncytitial Virus (RSV)
**note that this infection is lower down in the airways**
An older adult nursing home patient has sudden onset of fever, chills, headache, cough, sore throat, myalgia, and malaise. For the next week he eats very little and sleeps most of the day.
What is the syndrome and which virus causes it?
Grippe aka influenza-like illness (don’t know about virus, probably Influenza)
**know that this is a more systemic infection (hint from malaise, fever etc)
Describe the treatments for influenza and where in the viral replication cycle the drugs work
What tools are used to Dx flu?
See image below**
Flu Dx: for the most part, molecular diagnostics
Rapid Ag test
Nucleic acid detection test
RT-PCR Detection test
