RNA Viruses Flashcards
why is the next supervirus expected to be an RNA virus?
because they have high mutation rates that cause antiviral resistance and barrier to vaccines
what are some common features of RNA viruses
RNA is genetic material and template for protein synthesis, dual purpose of replication to copy genome and make mRNA
what is the difference between transcription and replication in RNA viruses?
transcription is mRNA synthesis, replication is RNA genome synthesis
what are the types of genomes and what do they mean?
dsRNA, + ssRNA and -ssRNA
positive strand is the sense strand and the same as mRNA
negative strand is the nonsense strand and the mRNA template
what is the extra step of + ssRNA replication and why does it occur?
a negative strand (template strand) must be made to amplify the genome and mRNA
what is RDRP and whose genome does it come from?
it is a RNA dependant RNA polymerase that comes from the viral genome (humans cannot perform this function)
where in the cell does RDRP act and why?
in the cytoplasm on cell membranes to concentrate components and increase efficiency
why are there more mutations in RNA viruses compared to DNA viruses and how does this change the intracellular environment?
RDRP does not proofread so there is a high error rate. this means a single cell has a mixture of wild types and mutants
what is recombination in viruses and what is the product?
similar to human recombination with large segment exchange, creates hybrid viruses that may have new features
what is reassortment in respect to RNA viruses?
segmented RNA viruses can mix their segments when infected with multiple strains. leads to new variants
what is a quasispecies?
a “sort of species” with a large amount of diversity among each type of virus
what type of genome does Poliovirus have?
+ ssRNA
what does poliovirus infect and how does it spread?
infects GI tract first and may spread to muscles and neurons by acquiring mutations
what is the reservoir and transmission of poliovirus?
persists in water and infects humans by fecal-oral rout
do all people who contract poliovirus have infection of motor neurons?
95% of people only have GI symptoms. Neurons involved with 1% of the 5% of people who have disseminated diesase
when does RNA synthesis switch from mRNA synthesis to genome synthesis in Poliovirus?
when capsid proteins accumulate
why is there little collision between RDRP and ribosomes in Poliovirus?
because translation happens first (RDRP scarce) and then - RNA synthesis occurs later
what type of vaccine is there for poliovirus?
live attenuated vaccine or killed virus
how does poliovirus enter the cell?
it interacts with multiple receptors on the cell surface and is endoxytosed. The virion is uncoated in the endosome and injects the genetic material into the cytoplasm by becoming hydrophobic
how and when is Poliovirus translated?
Translation occurs before RDRP makes the negative sense strand by ribosomes. The polyprotein is then cleaved.
what is the main clinical presentation of rotavirus?
profuse diarrhea, dehydration and maladsorption. peak incidence in winter
what is the classification of rotavirus?
reovirus, dsRNA, segmented, naked icosahedron
what is the classification of influenza?
orthomyxovirus - ssRNA, segmented, enveloped helical
what is the classification of HIV?
retrovirus +ssRNA 2 copies, enveloped icosahedron
is RDRP included in the rotavirus packaged in the virion?
yes, it is a -ssRNA virus
Where does transcription and translation occur in rotavirus?
transcription occurs within the loosened capsid and translation occurs in the cytoplasm
after assembly in the virus, what is the progression of rotavirus out of the cell?
virions bud into the rough ER and are either exocytosed by vesicles or lyse the cell during egress
what event happens to rotavirus after it exits the cell?
virions mature in the gut lumen
what is the treatment for rotavirus?
oral rehydration (make sure they are not contaminated)
is there a vaccine for rotavirus?
yes, a live attenuated vaccine
what are the symptoms of uncomplicated infuenza?
upper/lower respiratory tract involvement, muscle aches, fever, headaches and weakness
what are some complications that can be caused by influenza?
primary viral or secondary bacterial pneumonia (or mixture) or rhabdomyelitis (muscle breakdown)
where does transcription and replication of influenza occur?
inside the nucleus
how does influenza egress from the cell?
it buds off and is cleaved from surface receptors by neuraminidase to release into respiratory droplets
describe the genome of influenza
-ssRNA genome that is segmented into 8 portions
what are the two types of influenza vaccines?
fluzone (trivalent inactivated vaccine with two A subtypes and one B subtype) and flumist (live attenuated vaccine that is a mist)
describe antigenic shift and antigenic drift as it refers to influenza
antigenic shift refers to segment mis-sorting while antigenic drift refers to random mutations
what are three reasons that death rates due to HIV infection decreasing?
better treatments, hope for treatment to succeed and motivation for early diagnosis
what are the stages of HIV disease?
exposure, acute (primary) infection, seroconversion, latent period, early symptomatic infection, AIDS, and advanced HIV infection
what are the classifications of AIDS and advanced HIV infection?
AIDS- CD4 count<50 cells
what is HIV’s host range and tropism?
humans
CD4 cells and macrophages
what are the two mediators of HIV disease?
chronic immune activation and depletion of T cells and macrophages
if a patient comes in presenting with esophageal candidiasis, what virus would you also test for?
HIV
what is the first thing that HIV does when the virion fuses with the plasma membrane of a cell and uncoats?
Viral reverse transcriptase turns the + ssRNA into dsDNA in the cytoplasm. This is integrated into the host genome
what is the RNA product of HIV’s integrated DNA used for and how is it transcribed?
it is both the mRNA for translation and the viral genomes that will be packaged. It is transcribed with host RNA pol 2
how does HIV egress from the cell?
viral proteins and 2 copies of the genome bud from the cell.
what happens to the HIV virion once it leaves the cell?
capsid proteins are cleaved to form the final shape
why does HIV lie latent in the cell for a long time before replication?
when the T cell begins to divide, it supplies the virus with the necessary building blocks
how is HIV diagnosed?
serologic tests for antibodies, nucleic acid assay for viral load (molecular diagnostics) and CD4 T cell count
what are 4 ways to prevent HIV?
risk avoidance, community awareness, public health measures and chemoprophylaxis (antivirals0
what is the treatment for HIV?
combination of at least 3 drugs (avoid resistance)
what are 5 goals of HIV treatment?
suppress viral load, restore immune function, prevent transmission, prevent drug resistance and improve quality of life
