Influenza Flashcards
Influenza viruses are called ___________. Describe their structure, transmission.
- orthomyxoviruses
- enveloped, segmented, negative-sense RNA genome
- transmitted by body fluids
- have an RNA-dependent RNA polymerase that is packaged within the virus particle
What are the 2 main surface proteins of influenza?
- Hemaglutinin (HA)
- Neuraminidase (NA)
Functions of HA and NA
- HA: mediated binding to sialic acid on cells, mediates membrane fusion and virus entry (diff types of sialic acid linkages provide a barrier between cross-species transmission)
- NA: cleaves sialic acid; releases new viruses from surface of infected cell when budding occurs
Influenza causes seasonal _________ and usually people die from ____________.
- epidemics
- secondary bacterial pneumonia
Influenza is _______ every year. Some years it is _______ and termed a “bad flu year”. Rarely it is _______.
- endemic
- epidemic
- pandemic (world wide epidemic)
T/F: There is a an episodic nature to influenza infections.
-True
What was the deadliest pandemic of influenza infection and when did this occur?
-spanish flu of 1918
How is influenza spread? How long is its incubation period? What are symptoms? Are some particularly common in children? What immune response is generated? Does it disseminate? How long is one contagiously shedding the virus?
- respiratory transmission via body fluids; replicates in respiratory epithelium
- 1-4 days incubation
- abrupt fever onset, myalgia, sore throat, nonproductive cough, generalized muscle aches and malaise
- otitis ear infection common in children
- antibody and cell mediated immunity (1-2 weeks)
- viremia is rare
- shed in respiratory secretions for 5-10 days
What can and can’t rapid diagnostic influenza kits tell us?
- use nasal swabs
- low sensitivity and high specificity
- can distinguish A from B influenza, but not the type of A
How is influenza primarily diagnosed?
-Real time PCR tests are now used and can distinguish virus strains
Compare the histology of viral vs. bacterial pneumonia
- viral: relatively little intra-alveolar inflammation, rather have interstitial inflammation with mostly chronic lymphocytes; often affects bronchioles/bronchi-sometimes without alveolar involvement; can be cytopathic
- Bacterial: grow in airspaces so have alveolar inflammation and PMNs in airspaces as opposes to lymphocytes in alveolar walls as in viral
Compaire viral vs. bacterial pneumonia on xrays
- viral: typically more diffuse, increased interstitial markings; may resemble mycoplasma or legionella
- bacterial: typically a more localized, more whiting out appearance on xray (think pneumococcus)
Name and describe the 2 major complications of influenza
- secondary bacterial pneumonia: damage to ciliated epithelial cells, decreases mucociliary clearance, increased risk of bacterial pneumonia. Leading cause of death from influenza (esp. by S. aureus); rarely see brain infection (encephalopathy), heart infection (myo or pericarditis)
- Reye’s Syndrome: combination of influenza + aspirin in an infant can result in this; fatty liver change, acute encephalitis, high mortality
Reye’s Syndrome may affect all the organs of the body, but most seriously affected __________. Why is it life threatening?
- liver (fatty) and brain (edema)
- rapid development of severe neurological symptoms like lethargy, confusion, seizures, and coma make it life-threatening
What are the 3 types of influenza and describe their range of infection.
1 Influenza C: infects only humans, no epidemics; relatively rare, only causes minor respiratory symptoms
- Influenza B: infects only humans, mostly children, milder disease; can cause minor epidemics- not many strains
- Influenza A: large animal reservoirl highly variable with many strains; cause of most epidemics and ALL pandemics
What is the only influenza flavor to cause pandemics? Which causes most epidemics? Which is the worst clinically?
- A
- A, B does a few, and none for C
- A, then B, then C
Name the 3 surface proteins on an influenza A virus
- hemagglutinin (H)
- neuraminidate (N)
- M2 ion channel
What are the 2 general therapies for the flu and what surface protein do they target?
- Vaccine which targets H
- Drugs target N (Tamiflu) and M2 (Amantadine)
When determining immunity for influenza strains, which surface protein is the only one that truly matters? Give an example of what this means.
- H (hemagglutinin)
- H1N1 infected person will be immune to all H1, but not H2 or H3
What are the natural reservoirs for Influenza A?
- Birds, especially waterfowl
- all subtypes can be found in bird populations
T/F: Influenza B and C do not have subtypes because they do not mutate/evolve.
-False; they do evolve each year, so there are different strains of each, but they are not nearly as variable as Influenza A strains to be given different subtypes
What influenza strains have been the cause of seasonal flu for the past 30 years?
- H1N1
- H3N2