Respiratory Viruses Flashcards
What are the major causes of respiratory viral disease?
Influenza
Respiratory syncytial virus (RSV)
Also: parainfluenza, rhinovirus, coronavirus, enterovirus
What are the possible spectrum of diseases caused by viral respiratory illness?
Upper airway disease (runny nose, sore throat)
Bronchiolitis
Pneumonia
Acute respiratory distress syndrome (diffuse alveolar damage, respiratory failure)
Who is at highest risk for getting severe RSV disease?
Very young infants
Premature infants
Immunocompromised
Convenital heart or lung disease
** Almost everyone gets it by age 2, but it’s not always severe
What is the structure of RSV?
neg sense ssRNA, enveloped virus
Paramyxoviridae family (includes mumps, measles)
11 proteins in the genome, including F and G protein = surface glycoproteins, targets of immune response
What does the F protein in RSV do?
Fusion protein
Responsible for synctia formation: multinucleated giant cells
What does the G protein in RSV do?
Surface glycoprotein, mediates attachment
What is the pathogenesis of RSV?
Incubation period = 3-6 days, replicates in the cells of the upper airway, cna cause upper resp tract disease
Can spread to lower airway & cause croup, bronchiolitis, pneumonia, otitis media, apnea, wheezing
No viremia!
Duration of uncomplicated illness is 1-3 weeks
Immunity following infection is incomplete
What is the immune response to RSV?
Innate: surfactant, TLRs
Cell mediated immunity = antibodies against F and G protein
Pathology is due to the immune response
How is RSV diagnosed?
Clinical diagnosis
RTPCR
Viral culture = slow
How is RSV treated?
Supportive: O2, secretion management, monitor for apnea, intubation/ventillation if necessary
Bronchodilators, steroids – not really beneficial
Ribavirin – not used, not a good drug
How is RSV prevented?
Hand washing
Monoclonal antibody for high risk infants = palivizumab, targets F glycoprotein
Who is at risk to severe illness due to influenza?
Extremes of age
Pregnancy
Immunocompromised
What are the clinical manifestations of influenza?
ILI = influenza like illness – fever, chills, HA, myalgia, arthralgia, dry cough, nasal discharge
Young kids can get sepsis like syndrome, GI, croup, otitis media
What are complications of influenza?
Pneumonia
Bacterial super infection (S pneumo, S aureus, GAS)
Myocarditis
Encephalitis
Myositis
Reye syndrome (liver damage + encephalopathy)
How long is the incubation period of influenza? Duration of illness?
1-4 days incubation period
4-8 days of acute illness
1-2 weeks of convalescence (i.e. cough)
What is the structure of influenza virus?
neg sense ssRNA, enveloped
8 segments including HA and NA (which determine serotype)
What does HA of influenza do?
Hemagglutinin: viral attachment
Think H for Hugs
What dos NA of influenza do?
Neuroaminidas: Involved in viral budding from infected cells
Think N because it releases New viruses from cell
How does influenza infect a new cell?
HA helps it bind target cell
Then endocytosis brings it into cell – this is an acidic pocket, which activates viral glycoproteins to allow release of viral materials
viral RNA dependent RNA pol transcribes + sense RNAs to make viral proteins
Host RNA polymerase makes new neg sense RNAs for new virions
Viral assembly
New viruses go to cell membrane & still attached until sialidase cleaves it –> released to infect other cells
How long does viral replication occur? How long does viral shedding continue?
1-3 days of replicatoin
Shedding for 7-10 days
What cells does influenza infect? What is the result?
Columnar epithelial cells of the respiratory tract
Result is epethelial destruction, increased mucous production, ciliarly stasis
What is antigenic shift?
Slow change of viral surface antigens over time
Due to lack of proofreading of RNA polymerase
This is why not all viruses of the same strain are identical & you get resistance to vaccine/meds
What is antigenic drift?
Sudden, rapid change i.e. H1 to h3
Responsible for pandemics
Due to reassortment of segments during viral packaging and release
What is a pandemic?
When there’s sustained human to human transmission of influenza
Why is it so bad to get influenza + superinfection?
Synergistic effect: you get so much infiltrate & its bad news
How do you diagnose influenza?
PCR
How is influenza treated?
Uncomplicated = supportive
Antiviral agents: reserved for high risk patients
Amantidine, rimantidine: block influenza A M2 channel, which promotes viral uncoating – no activity against influenza B. Give within 48 h of symptoms
Oseltamivir (tamiflu), zanamivir: Neuroaminidase inhibitors. Give within 72 h of symptoms
How is influenza prevented?
Influenza vaccine
What are the 2 types of vaccines? Who can get them? Who can’t get them?
TIV: trivalent inactivated – for anyone over age 6 months, no egg allergy
LAIV: live attenuated intranasal – 2-49 years old
Not if egg allergy, immunocompromised, taking aspirin, history of Guillain Barre syndrome, asthma, pregnant women, person in close contact with hospitalized bone marrow transplant recipients
What causes death from influenza?
- exacerbation of underlying illness
- bacterial superinfection
- sudden severe disease (fulminant) after initial mild illness
What is Guillain Barre syndrome?
Autoimmune disorder
Acute inflammatory demyelinating polyneuropathy of peripheral nervous system
Triggered by an acute infectious process
Presents as ascending paralysis
Treat wtih supportive care, plasmapheresis, IV Ig’s –> full recovery
