(+) Strand RNA Viruses

Question 1

Describe at least 5 common features of (+) Strand RNA Viruses.

Answer 1

1. replicate in cytoplasm
2. Genomic RNA serves as message and is DIRECTLY translated
3. Genomic RNA is infectious
4. Virions LACK enzymes
5. Viral proteins are translated as Polyproteins.

Question 2

List the 2 non-enveloped, viral families of (+) strand RNA viruses.

Answer 2

1. Picornaviridae (enteroviruses and rhinoviruses)

2. Caliciviridae

Question 3

Briefly describe the features of the 2 major types of Picornaviridae.

Answer 3

1. Enteroviruses grow at 37 C in the GI and are acid stable. Transmitted by fecal-oral contamination.
2. Rhinoviruses grow at 33 C in the nose and are acid labile. Can be transmitted through fomites and enters host cells via ICAM-1

Question 4

List the 3 enveloped, (+) RNA strand virus families.

Answer 4

1. Togaviruses (icosahedral)
2. Flaviviruses (icosahedral)
3. Coronaviruses (helical)

Question 5

Describe 2 special features of the viral (+) strand genome RNA.

Answer 5

1. PolyA sequence at 3’ end

2. vPg bound to 5’ end of viral RNA

Question 6

Define the purpose of the internal ribosomal entry site in 5’ UTR of viral genome.

Answer 6

Since there is no 5’ cap, ribosomes recognize viral IRES to start translating the message. Polio uses a cap-independent process.

Question 7

Describe how the virus shuts off protein synthesis of the infected cell.

Answer 7

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)

Question 8

Explain the significance of RNA-dependent RNA Polymerase in polio virus.

Answer 8

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.

Question 9

Explain the significance of anti-sense RNA strand.

Answer 9

This is made from the template (+) sense RNA strand. (+) strands are made in XS over (-) strands.

Question 10

Describe the polio paradox.

Answer 10

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).

Question 11

Explain how the MOA of poliovirus manifests clinically.

Answer 11

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.

Question 12

What is the significance of paralytic polio?

Answer 12

Only 1% of polio-virus infections result in aseptic meningitis or paralytic polio (respiratory paralysis or muscle weakness)

Question 13

Explain how the Sabin vaccine is more advantageous to the original Salk vaccine.

Answer 13

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.

Question 14

List 4 common features of enveloped (+) strand RNA viruses.

Answer 14

Flaviviruses and Togaviruses are…

1. non-segmented (+) strand genome
2. Enveloped
3. Most are “arthropod-borne”
4. Bud off from internal organelles

Question 15

Explain what is meant by “accidental” or “dead-end hosts” as it relates to alphaviruses.

Answer 15

Dead-end hosts have blood levels of viral particles that aren’t high enough for mosquito vectors to transfer the virus to another organism.

Question 16

Define some features of the Chikungunya virus.

Answer 16

1. Humans and primates are hosts, mosquitoes are vectors
2. Outbreaks occur in Africa, Asia and Europe (only recently did they come to the US, Florida)
3. Presents as arthritis-related ailments (joint pain, headaches and rashes).

Question 17

These types of alpha-viruses feature humans and horses as accidental hosts. Which is more severe?

Answer 17

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)

Question 18

Define the mode of transmission, symptoms and vaccine for the Rubivirus.

Answer 18

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

Question 19

For what 3 types of Flaviviruses are humans the accidental hosts?

Answer 19

Japanese Encephalitis Virus, Saint Louis Encephalitis Virus and West Nile Virus

Question 20

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.

Answer 20

Japanese Encephalitis virus

Question 21

This type of flavivirus appears in the elderly, in which 20% of those infected are symptomatic (fever, headaches, muscle weakness (GBS)); 10% fatality rate.

Answer 21

West Nile Virus

Question 22

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

Answer 22

Saint Louis Encephalitis Virus

Question 23

Compare and contrast Classic Dengue Fever from Dengue Hemorrhagic Fever and Shock Syndrome.

Answer 23

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.

Question 24

Describe the MOA for Dengue Hemorrhagic fever and Shock Syndrome.

Answer 24

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.

Question 25

Compare and contrast the 2 types of Yellow Fever and how they spread.

Answer 25

1. Jungle yellow fever is spread from monkey to monkey via Haemagogus mosquitoes.
2. Urban yellow fever is spread from human to human via Aedes mosquitoes.

Question 26

Briefly describe the transmission and symptoms of someone infected by Zika virus.

Answer 26

Flavivirus transmitted by Aedes mosquito; asymptomatic/ mild fever, rash, arthralgia in person; microcephaly of child from pregnant mother

Question 27

Briefly describe the replication strategy, serology, symptoms and treatment of Hepatitis C.

Answer 27

Replication strategy similar to Flaviruses; > 6 serotypes that are constantly changing the hyper-variable region on glycoprotein envelope; transmitted by blood (IV use, sex or transplacentally); Can present as acute hepatitis in 25% of cases or hepatocellular carcinoma years later; Treatment with Acyclovir

Question 28

Explain how the onset of Hepatitic C can put someone at risk of developing liver cancer.

Answer 28

Viral killing of hepatocytes and immune response causes the liver cells to regenerate. Chronic infection can lead to enhanced hepatocellular carcinoma in the future. Cirrhosis and alcoholism can put people at risk of developing this too.

Question 29

Describe some features of the Corona-viruses.

Answer 29

1. Glycoprotein spikes appear as a crown
2. Helical nucleocapsid
3. Respiratory tsm and the presentation of common cold

Question 30

Briefly describe 2 examples of corona-viruses.

Answer 30

1. SARS = presents as pneumonia, spread quickly by respiratory aerosols, 10% fatality
2. MERS-CoV = Severe acute respiratory illness; spread by close contact, 40% fatality; recently introduced to USA.

Question 31

Describe the transmission, clinical features and prophylactic treatment of: Rubivirus (Rubella)

Answer 31

Tsm: Respiratory droplets (not an arbovirus);
Cx: fever, headache, sore throat, lymph nodes, rash;
Prophylaxis: MMR live attenuated vaccine

Question 32

What are the TORCHeS infections?

Answer 32

Toxoplasma gondii,
Rubella,
CMV,
HIV/HSV,
Syphillis

Question 33

Name at least 3 symptoms that can be experienced with Congenital rubella syndrome (CRS).

Answer 33

1. Patent ductus arteriosus
2. Cataracts
3. Sensory-neural deafness
4. Jaundice, Blue-berry muffin rash

Question 34

Describe the transmission, clinical features, diagnosis and treatment for: Coronavirus

Answer 34

Tsm: respiratory;
Cx: common cold, SARS, MERS-CoV (40% fatality!);
Dx: PCR without antibodies;
Tx: Corticosteroids, Ribavirin

Question 35

How do Flaviviruses and Togaviruses differ?

Answer 35

Transcriptional pattern;

Transmission: Flaviviruses via mosquitoes; Togaviruses via mosquito (except Rubella virus via respiratory route)

Question 36

What accounts for the repeated outbreaks of Norovirus (Norwalk) on cruise ships?

Answer 36

Stability of virus within the environment and relative resistance to disinfection. It causes explosive watery diarrhea. Those at risk are children, raw shellfish eaters, and cruise ship attendants.

Question 37

Describe at least 4 features of Picornaviruses.

Answer 37

1. Small
2. Icosahedral
3. Naked (non-enveloped)
4. Transmitted via digestive tract or respiratory tract

Question 38

What type of virus is Coxsackievirus? Name a few symptoms.

Answer 38

Enterovirus within the Picornavirus family. Results in Meningitis, Hand-foot-and-mouth Disease, pleurodynia and dilated cardiomyopathy.

Question 39

Define the 2 major types of Togaviruses.

Answer 39

1. Arbovirus - Eastern, Western and Venezuelan Equine viruses (spread by mosquitoes)
2. Rubella - Rubivirus (spread by respiratory transmission)

Question 40

How does Polio virus genome differ from typical mammalian mRNA? What is the significance of this feature?

Answer 40

Has a small protein (IRES) covalently bound to the 5’ (UTR) end of the mRNA. This allows polio viruses to translate viral message in a cap-independent manner.

Question 41

What type of Flavivirus is transmitted by Aedes Egyptian mosquito and manifests as “Breakbone fever”?

Answer 41

Classic Dengue Virus - Dengue fever (terrible joint and bone pain, even after recovery); Hemorrhagic fever -> thrombocytopenia

Question 42

What type of Flavivirus is associated with a lot of dead birds (reservoir) in which humans are the dead end host? List the symptoms.

Answer 42

West Nile Virus - 20% symptomatic for fever, headaches, muscle weakness; <1% encephalitis/paralysis