Introduction to Virology

Question 1

Viruses are responsible for ____ disease worldwide

Answer 1

50%

Question 2

Why else are viruses important?

Answer 2

they are linked to 15-20% of cancers; they can be used as future tools for vaccines

Question 3

Virus

Answer 3

disease causing entity at the boundary of life and non-life; all of nucleic acid genome; all are obligate parasites

Question 4

Features of all viruses + features that some have

Answer 4

all = DNA or RNA + capsid
some = matrix, lipid envelope, glycoproteins

Question 5

Many viruses use what type of capsids

Answer 5

icosahedral, with 3 capsomeres per face and a minimum of 20 faces

Question 6

2 examples of naked capsid viruses

Answer 6

bacteriophage and adenovirus

Question 7

you can classify viruses by nature of capsid

Answer 7

naked capsid (which can be helical or icosahedral) or enveloped (which can be helical, icosahedral, or complex)

Question 8

you can also classify by nature of genome

Answer 8

DNA or RNA (which both break down into SS or DS)

Question 9

Group IV viruses are + strand RNA viruses…what does this mean for their infectivity and replication strategy

Answer 9

the positive strand RNA is infectious because it can be introduced into the cell and directly translated into proteins
replication strategy- they will make a negative strand to serve as a template for making more positive strands

Question 10

Group VI viruses like HIV have a particular genome that leads to their replication strategy…

Answer 10

they have a positive stranded RNA with extra sequences for genome amplification and packaging…reverse transcription into dsDNA is a must

Question 11

Group III viruses are weird (rotavirus = example)…

Answer 11

they come in a vesicle, they have their own RNA-dependent RNA pol, they make a positive strand which leaves the vesicle to be packaged or translated. In a capsid, the positive strand is used to make a negative strand (hence dsRNA). The cells can’t melt the dsRNA (which is good because you want the cells to be very good at recognizing dsRNA as foreign to maintain the IFN-innate response) but the viral enzymes can.

Question 12

sense strand

Answer 12

mRNA made from the DNA template strand (the anti-sense strand)..it is the positive strand and it will read directly the same as the complementary DNA strand to the template

So, if you have a positive mRNA sense strand, you can find the DNA template by matching the complementary bp to it

Question 13

Negative strand viruses must

Answer 13

have their RNA copied by a RNA dependent pol into a positive sense strand- it is am amplification step to make lots of mRNA and lots of protein

Question 14

Picornaviruses (polio) and flaviviruses (west nile, dengue)

Answer 14

genome = positive-strand RNA
virion RNA dependent polymerase? no
initial event in cell= translation
genome infectivity = infectious

Question 15

orthomyxovirus (flu) and paramyxovirus (measles and mumps)

Answer 15

genome = negative-strand RNA
virion RNA dependent polymerase? yes
initial event in cell = transcription
genome infectivity = non-infectious

Question 16

reovirus (rotavirus)

Answer 16

genome = ds RNA
virion RNA dependent polymerase? yes
initial event in cell = transcription
genome infectivity = no

Question 17

retrovirus (HIV)

Answer 17

genome = positive strand RNA
virion RNA dependent polymerase? yes
initial event in cell = reverse transcription
genome infectivity = no

Question 18

6 basic steps of viral replication

Answer 18

1. attachment
2. entry/ penetration
3. uncoating
4. protein expression/ gene replication
5. assembly
6. release

Question 19

Steps that have to deal with viral receptors

Answer 19

1 and 2 (attachment and entry)

Question 20

Viral receptors allow virus to:

Answer 20

1. find the appropriate host cells
2. interact with virus to allow for absorption
3. interact to facilitate entry
4. facilitate disassembly of viral capsid

Question 21

absorption is aided by charged molecules on the surface….what are they

Answer 21

sialic acid- flu, coronavirus, rhinovirus
heparin sulfate proteoglycans- herpes, dengue, adeno-associated viruses
charged lipids - VSV

Question 22

examples of cell surface proteins that serve as receptors or co-receptors for viruses

Answer 22

integrins- adenoviruses, Kaposi's sarcoma, cocksackie
NAChR - rabies
HAVCr-1 - hep a/ ebola/ dengue
CD4- HIV and herpes 7 
PVR/CD155- poliovirus

Question 23

3 main modes for uncoating

Answer 23

1. uncoating at plasma membrane (paramyoxvirus - RSV and mumps)
2. uncoating in endosomes (alpha virus- Chikungunya and semiliki forest virus)
3. uncoating at the nuclear membrane (adenovirus)

Question 24

transcription and replication of genome (step 4)

Answer 24

many different methods; can copy using viral or host enzymes; can occur in cytoplasm or nucleus

Question 25

proteins encoded by viruses

Answer 25

structural- capsid, envelope | enzymatic- proteases, integrases

Question 26

proteins encoded by viruses can be made and used within the host cell

Answer 26

enzymatic functions necessary for virus to block innate and adaptive immune responses to affect host cell growth and survival (viral oncogenes) regulate cellular or viral gene expression

Question 27

3 mechanisms of release

Answer 27

enveloped- budding non-enveloped- lysis of cell shedding into mucosal linings

Question 28

4 major ways that viruses cause disease

Answer 28

1. direct tissue damage (like in the liver with hep b or nerve damage in poilio or herpes) 2. inflammation (cytokines associated with viral infection cause flu like symptoms) 3. cancer (deregulated growth like with papilloma virus) 4. loss of immunocompetency (HIV with depletion of CD4 cells)

Question 29

Pathogenic outcomes of infection

Answer 29

cytopathic effects (CPE) death of the host cell (cytocidal) non-lethal shedding abortive infection persistent infection (latency) - herpes or HIV cellular transformation (HPV, EBV, KSHV can immortalize and transform the cell and give rise to tumors)

Question 30

Our immune system operates constantly with a background of

Answer 30

viral infection and chronic inflammation- for example ERV and CMV are common and normally with us

Question 31

Where do emerging viruses come from?

Answer 31

reassortment with existing viruses and from zoonosis (jump from animals to humans)

Question 32

Example of zoonosis

Answer 32

Ebola- fruit bats eat fruit and infect it with ebola. Duiker eat the fruit and then humans hunt the duiker

Question 33

Zoonosis is facilitated by

Answer 33

modern transport and pushing into more remote areas

Question 34

more than _____ % of infectious disease agents are zoonosis

Answer 34

60

Question 35

Explain the meaning of intermediary species

Answer 35

for example, the host of Mers-CoV is a bat, but transmission to humans is via camels and many times the intermediary between those two is a mosquito

Question 36

Bats harbor

Answer 36

``` haemorraghic fever viruses (Ebola, Marburg) respiratory viruses (SARs and MERS-CoV) Henipah viruses (hendra, Nipah) ```

Question 37

Primates

Answer 37

HIV monkeypox Chikungunya, dengue, yellow fever

Question 38

Bird

Answer 38

avian flu and west nile virus

Question 39

Rodents

Answer 39

hantavirus, lassa fever

Question 40

initiative to closely address animal-human-ecosystem interface

Answer 40

OneHealth