Exam #4: Viral Infections of the Resp. Tract II Flashcards
List the characteristics of the Influenza virus.
- Orthomyxovirus
- -ssRNA
- Segmented,
- Enveloped (the envelope contains H & N)
- Hemagluttinin= viral attachment protein
- Neurominidase= cleaves sialic acid to aid in virion spread
What is the function of Hemagglutinin (H)?
- Attachment to host
- Agglutinates RBCs
What is the function of Neuraminidase (N)?
- Cleaves sialic acid
- Virion release
- Virion spread
What is antigenic drift?
- Small changes in virus e.g. H & N in Influenza
- Driven by point mutations made by RNA polymerase
- Significant changes occur every 2-3 years
*Why there are changes to the Influenza vaccine each year
What is antigenic shift & how is it different from antigenic drift?
- Large changes in H & N
- Driven by re-assortment of two viruses
- Requires co-infection of the same cell (less common than antigenic drift)
*The cause of pandemics
Describe the mechanism of re-assortment.
- Two different strains of a virus infect the same cell
- Replication occurs
- Assembly of virions is a “re-assortment” of viral particles
What kind of re-assortment is the most concerning in influenza?
Animal & Human strains re-assorting
E.g. Avian flu & Human flu reassortment
What are the barriers to re-assortment of human & animal species of Influenza?
Specializations for infection of humans vs. animals make it difficult for infection to occur simultaneously
I.e. human flu is good at infecting humans, avian flu is good at infecting birds, they’re both not very good at infecting the opposite. Since reassortment requires that a cell be infected with BOTH at the same time, this is a significant barrier.
What are the three different types of Influenza virus?
A, B & C
What are the characteristics of Influenza virus A? Specifically address # of genome segments, host range, disease severity, epidemic potential, and antigenic change.
- 8 segments
- Host= Humans, swine, avian, equines, marine mammals
- Disease often severe
- Causes Epidemics & Pandemics
- Undergoes antigenic drift & shift.
What are the characteristics of Influenza virus B? Specifically address # of genome segments, host range, disease severity, epidemic potential, and antigenic change.
- 8 segments
- Host= Humans ONLY
- Disease is occasionally severe
- Can cause outbreaks and occasional epidemics
- Undergoes antigenic drift ONLY
What are the characteristics of Influenza virus C? Specifically address # of genome segments, host range, disease severity, epidemic potential, and antigenic change.
- 7 segments
- Host= humans & swine
- Disease is usually mild
- Causes limited outbreaks
- Undergoes antigenic drift ONLY
So mild that vaccines are not even generated against Type C.
Which is the only type of influenza virus to be associated with antigenic shift?
Influenza A (most severe)
How are influenza viruses named clinically?
Serotype Location Isolate Year Hemagglutinin Subtype Neuraminidase Subtype
Which parts of the influenza virus are associated with antigenic shift?
H & N subtypes
What parts of the influenza virus are associated with antigenic drift?
Location
Isolate
Year
Outline the algorithm for antiviral treatment in influenza.
1) Mild or uncomplicated illness?
2) Does the patient have any Risk Factors?
Risk Factors= Treat with antiviral
No Risk Factors= If within 48 hours of the onset of symptoms, may consider antiviral
For both, provide instructions for symptomatic care, infection control, and return if no improvement in 72 hours
What are the classes of antivirals for influenza infection?
- Ion channel blockers
- Neuraminidase Inhibitors
What is the mechanism of action of Ion channel blockers?
Blocks replication prior to genome release by blocking the M2 ion channel
*Note that these are only effective against Influenza A & that most circulating Influenza A strains are resistant. CDC does NOT recommend their use.
