Clinical Presentation
Which symptoms most commonly distinguish influenza from the common cold?
Sudden onset of high fever, myalgia, and profound fatigue.
Which influenza type can infect both humans and animals?
Influenza A.
Which part of the respiratory tract does influenza primarily infect?
Upper and lower respiratory epithelium.
What type of nucleic acid is in the influenza genome?
Single-stranded negative-sense RNA.
What receptor does hemagglutinin bind to on host cells?
Sialic acid receptor.
What is the typical duration of influenza symptoms in healthy adults?
About 5–7 days.
Why does influenza B not cause pandemics?
It has no animal reservoir; only infects humans.
What host immune response contributes to flu symptoms like fever and myalgia?
Cytokine release (e.g., IL-1, TNF-α).
How many segments make up the influenza genome?
Eight RNA segments.
Where in the host cell does influenza replication occur?
In the nucleus (unique for an RNA virus).
Which populations are at highest risk of influenza complications?
Elderly, young children, pregnant women, and immunocompromised patients.
What global event does influenza A cause approximately every 10–40 years?
Pandemics due to antigenic shift.
How does viral destruction of epithelial cells affect the respiratory system?
Impairs mucociliary clearance, predisposing to secondary bacterial infections.
Name the two major surface glycoproteins of the influenza virus.
Hemagglutinin (HA) and neuraminidase (NA).
What process allows influenza to leave the host cell after replication?
Budding, assisted by neuraminidase.
What complication is more associated with influenza B, especially in children?
Reye’s syndrome (when aspirin is used).
Which hemisphere experiences flu season from May to October?
The Southern Hemisphere.
What is the main difference in pathophysiology between influenza A and B?
A can reassort its genome with animal strains (shift), while B cannot.
What is the function of the M2 protein?
Acts as an ion channel aiding in viral uncoating.
Which step in the life cycle is blocked by amantadine?
Uncoating (via inhibition of M2 ion channel).
Describe how the clinical presentation differs between influenza A and B.
Influenza A often more severe and widespread (pandemics); Influenza B typically milder and seasonal.
Explain the difference between epidemic and pandemic influenza.
Epidemic = localized outbreak; pandemic = global spread due to major antigenic change (shift).
What secondary infection is a common cause of death following influenza?
Bacterial pneumonia (often Streptococcus pneumoniae or Staphylococcus aureus).
Which structural feature of the virus allows antigenic shift to occur?
Segmented genome enables reassortment between strains.
Why must influenza bring its own RNA-dependent RNA polymerase?
Because host cells cannot transcribe negative-sense RNA.