B5: influenza Flashcards
What is influenza?
An acute contagious disease of the upper and lower respiratory tracts caused by negative-strand, segmented RNA viruses of the family Orthomyxoviridae.
Where does the name ‘influenza’ come from?
The Italian phrase “un’influenza di freddo,” meaning “influence of the cold.”
Why is influenza responsible for seasonal epidemics and major pandemics?
Due to antigenic drift and antigenic shift, which allow the virus to evade immunity and cause new outbreaks.
How is influenza transmitted?
Through respiratory droplets, direct contact with infected secretions, and contaminated surfaces.
What are the primary symptoms of influenza?
Sudden onset of high fever, muscle/joint aches, exhaustion, headache, and malaise.
When do influenza infections peak?
Most common between November and February.
What factors influence an individual’s susceptibility to influenza?
Age, immune status, underlying conditions, and prior exposure to influenza viruses.
What are potential complications of influenza?
Pneumonia (primary viral or secondary bacterial), Reye’s syndrome, and multi-organ failure in severe cases.
What is Reye’s syndrome, and how is it linked to influenza?
A rare but serious condition causing encephalitis, hepatic and renal failure, often associated with aspirin use in children with influenza B.
Rank the severity of different influenza viruses in humans.
Influenza A > Influenza B > Influenza C/D.
Which family do influenza viruses belong to?
Orthomyxoviridae.
What are the four types of influenza viruses?
Influenza A, B, C, and D.
What is the basic structure of the influenza A virion?
Enveloped virus with membrane proteins (HA, NA, M2), a matrix layer (M1), and an RNP complex containing 8 RNA segments.
What type of genome does influenza A have?
A negative-sense, segmented RNA genome (8 segments)
What are the major surface proteins of influenza A?
Hemagglutinin (HA), Neuraminidase (NA), and M2 ion channel.
What is the function of HA in influenza?
HA binds to sialic acid on host cells, mediating viral entry.
What does NA do in influenza virus replication?
Cleaves sialic acid residues, allowing viral release from the host cell.
How many genome segments does influenza A have?
8 RNA segments coding for at least 17 proteins.
What does the M2 ion channel do?
Regulates pH inside the virion, aiding uncoating during entry.
How does influenza enter host cells?
Via endocytosis, mediated by HA binding to sialic acid receptors.
Why is endosomal acidification important for influenza infection?
It triggers HA conformational changes, leading to membrane fusion and RNP release.
Where does influenza genome replication occur?
In the nucleus, unlike most RNA viruses.
How does influenza produce mRNA?
The viral polymerase “cap-snatches” host pre-mRNA caps to prime viral mRNA synthesis.
