Segmented Viruses Flashcards
Orthomyxoviridae characteristics?
-Group 5–>(-)ssRNA
-enveloped
-helical
-segmented
-replicates in NUCLEUS not cytoplasm
-cap-snatching
What is an advantage and disadvantage to being segmented?
Adv: Genes can be individually transcribed b/c diff promoters
Disadv: All segments need to be in genome to be infectious–>if missing even just 1 segment = NOT INFECTIOUS
Where does influenza virus replicate?
NUCLEUS
How many segments does influenza virus usually have?
7 or 8 segments
How do segmented viruses rapidly evolve?
Reassortment of segments
Genetic drift (Antigenic drift in flu)
Changes that happen because of error prone polymerase
-point mutations, insertions, deletions
Genetic shift (Antigenic shift in flu)
Changes that happen because of reassortmnet
Which causes bigger changes, genetic drift or shift
Genetic shift
What pathogens are in Orthomyxoviridae?
Influenza A, B, and C
Which strain of influenza are pandemic and why?
Influenza A because it has animal hosts and can get new segments through antigenic shift
Why was the Spanish flu unique?
Infected mostly healthy adults
How does influenza enter?
Hemagglutinin (HA) binds to sialic acid
How does influenza exit?
Neuraminidase (NA) cleaves sialic acid
What is the reservoir for influenza?
Water fowl
True or false: Birds can directly infect humans
FALSE
-Birds have 2,3 sialic acid bond while humans have 2,6 so they cannot infect
-Need intermediate host like pigs that have both 2,3 and 2,6
-Bird infect–>pig infects–>human
True or false: Novel influenza strains (pandemic) come from reassorted strains
True
Why do we need a new flu vaccine every year?
Flu viruses evolve through antigenic drift which causes 1 strain of flu to be selected and take over every year
Where does influenza make its proteins and packaging?
Cytoplasm
True or false: Proteins can get translated in nucleus
False
-there are no ribosomes in nucleus
-mRNA translation/proteins are made in cytoplasm
What is cap-snatching?
Segmented viruses steal 5’ ends from host (10-20 bp) to start their transcription
What are 3 advantages of cap-snatching?
- Don’t have to encode capping machinery
- Nor recognized by immune system
- Shuts off host translation
Where does alternative splicing only happen?
Nucleus
What is an advantage for influenza by replicating in nucleus?
Can use host alternative splicing machinery to make more different types of proteins
How can we inhibit influenza?
-Zanamivir
-Tamiflu
-act as sialic acid–>NA will bind to this instead of actual sialic acid–>sialic acid will not be cleaved–>virus cannot exit & replicate
Bunyavirales characteristics
-Group 5–>(-)ssRNA
-segmented
-enveloped
-cap snatch
-helical
-replicates in CYTOPLASM
-only 2-3 segments
What pathogens are in Bunyavirales?
-Lassa virus (mouse)
-Haantan and Sin Nombre ( mouse)
Rift valley fever (Arbovirus-mosquito)
-Crimean-Congo hemorrhagic fever (Arbovirus-tick)
True or false: Lassa spreads human to human
False
-Does not spread person to person
-Get it by coming into contact with mouse urine/feces
Reoviridae characteristics
-GROUP 3–>dsRNA
-segmented
-replicates in cytoplasm
-non enveloped
-icosahedral
-transcription happens INSIDE CAPSID
-10 to 12 segments
Why do reoviridae need to replicate inside capsid?
If dsRNA was in cytoplasm the cell would do an immune response so it stays in the capsid shell
How do reoviridae enter and exit?
Non enveloped
-Entry: penetrate membrane
-Exit: lysis
Is it surprising that reoviridae can cause diarrhea?
No since it is non enveloped it is environmentally stable and can live in GI tract
What pathogens are in reoviridae?
Rotavirus
