(+) Strand RNA Viruses Flashcards
(42 cards)
Describe at least 5 common features of (+) Strand RNA Viruses.
- replicate in cytoplasm
- Genomic RNA serves as message and is DIRECTLY translated
- Genomic RNA is infectious
- Virions LACK enzymes
- Viral proteins are translated as Polyproteins.
List the 2 non-enveloped, viral families of (+) strand RNA viruses.
- Picornaviridae (enteroviruses and rhinoviruses)
2. Caliciviridae
Briefly describe the features of the 2 major types of Picornaviridae.
- Enteroviruses grow at 37 C in the GI and are acid stable. Transmitted by fecal-oral contamination.
- Rhinoviruses grow at 33 C in the nose and are acid labile. Can be transmitted through fomites and enters host cells via ICAM-1
List the 3 enveloped, (+) RNA strand virus families.
- Togaviruses (icosahedral)
- Flaviviruses (icosahedral)
- Coronaviruses (helical)
Describe 2 special features of the viral (+) strand genome RNA.
- PolyA sequence at 3’ end
2. vPg bound to 5’ end of viral RNA
Define the purpose of the internal ribosomal entry site in 5’ UTR of viral genome.
Since there is no 5’ cap, ribosomes recognize viral IRES to start translating the message. Polio uses a cap-independent process.
Describe how the virus shuts off protein synthesis of the infected cell.
Viral proteases cleave a critical protein in initiation complex that would scan AUG codon. This disables synthesis of cellular proteins, but allows viral protein synthesis (because it is cap-independent)
Explain the significance of RNA-dependent RNA Polymerase in polio virus.
This early enzymatic RDRP enables the virus to make more RNA, since mammalian cells only make RNA from DNA. This makes an “anti-sense” (-) strand to serve as a template for (+) strand RNA.
Explain the significance of anti-sense RNA strand.
This is made from the template (+) sense RNA strand. (+) strands are made in XS over (-) strands.
Describe the polio paradox.
The worst polio outbreaks started 200 years ago in more developed parts of the world. Although, virus is highly infectious most newborns (before the hygiene advent) had maternal ABs for protection. This resulted in more severe diseases and epidemics (before the Salk vaccine).
Explain how the MOA of poliovirus manifests clinically.
Poliovirus is an enterovirus that is asymptomatic in the GI tract. Once it enters the blood it can travel to the spinal cord or lungs to result in respiratory paralysis or club foot.
What is the significance of paralytic polio?
Only 1% of polio-virus infections result in aseptic meningitis or paralytic polio (respiratory paralysis or muscle weakness)
Explain how the Sabin vaccine is more advantageous to the original Salk vaccine.
Oral Sabin vaccine had better coverage and spurred an effective IgG response in kids. The problem arose from recombination between wild-type and vaccine strain to cause activated polio in recipients.
List 4 common features of enveloped (+) strand RNA viruses.
Flaviviruses and Togaviruses are…
- non-segmented (+) strand genome
- Enveloped
- Most are “arthropod-borne”
- Bud off from internal organelles
Explain what is meant by “accidental” or “dead-end hosts” as it relates to alphaviruses.
Dead-end hosts have blood levels of viral particles that aren’t high enough for mosquito vectors to transfer the virus to another organism.
Define some features of the Chikungunya virus.
- Humans and primates are hosts, mosquitoes are vectors
- Outbreaks occur in Africa, Asia and Europe (only recently did they come to the US, Florida)
- Presents as arthritis-related ailments (joint pain, headaches and rashes).
These types of alpha-viruses feature humans and horses as accidental hosts. Which is more severe?
Eastern-Equine Encephalitis virus (wild bird-mosquito tsm; 50% fatality); Western-Equine Encephalitis Virus (less severe and more frequent); Venezuelan Equine Encephalitis (Rodent-mosquito tsm)
Define the mode of transmission, symptoms and vaccine for the Rubivirus.
Rubella is spread by respiratory tsm; symptoms include fever, sore throat and runny nose; Congenital rubella syndrome (CRS) is SEVERE for fetuses; MMR is the successful live attenuated vaccine
For what 3 types of Flaviviruses are humans the accidental hosts?
Japanese Encephalitis Virus, Saint Louis Encephalitis Virus and West Nile Virus
This type of Flavivirus is transmitted between pigs, aquatic birds. Humans are the accidental host. Severe disease presents with an altered mental status, seizures and is 20-30% fatal. In inactivated vaccine exists.
Japanese Encephalitis virus
This type of flavivirus appears in the elderly, in which 20% of those infected are symptomatic (fever, headaches, muscle weakness (GBS)); 10% fatality rate.
West Nile Virus
This type of flavivirus presents as an abrupt onset of fever, dizziness and nausea; 90% of elderly develop severe CNS disease; with a 15% fatality rate
Saint Louis Encephalitis Virus
Compare and contrast Classic Dengue Fever from Dengue Hemorrhagic Fever and Shock Syndrome.
Classic dengue = breakbone fever where terrible joint/bone pain lasts months after recovery with little mortality;
Dengue Hemorrhagic Fever = 10% fatal with shock and bleeding at GI and in skin.
Describe the MOA for Dengue Hemorrhagic fever and Shock Syndrome.
4 serotypes result in a neutralizing AB that’s not cross reactive. Ag-AB complexes form > activates complement > cytokines are released > HUGE immunological reaction ensues. Vasopermeability from complement. Shock from infection of macrophages.
