Introduction to Virology

Question 1

What are 3 general ways you can classify a virus?

Answer 1

1. on it’s genome structure
2. general structural characteristics (enveloped/ shape?)
3. Infection characteristics - the disease it causes and how it causes it

Question 2

Wha tis the final taxonomic classification of viruses?

Answer 2

the genome sequence

Question 3

What is the capsid? What is the nucleocapsid?

Answer 3

the capsid is a protein shell that surrounds the genome of a virus particle

the nucleocapsid is the capsid complexed with the nucleic acid of the virion

Question 4

What is the capsid composed of?

Answer 4

protein subunits called capsomere

Question 5

What lies between the envelope and the capsid in an enveloped virus?

Answer 5

the integument (not all)

Question 6

What are the two main shapes of capsids?

Answer 6

helical (rod-shaped viruses)

icosahedral (spherical viruses - this is the most efficient arrangements of subunits in a closed shell)

Question 7

Give details about the measles virus…

genome (group)

segmented?

shape?

enveloped?

Answer 7

ssRNA - (group 5)

nonsegmented

helical nucleocapsid

enveloped

(paramyxoviridae, morbillivirus)

Question 8

Provide details about the Coxsackievirus B…

genome (group)

segmented?

capsid shape?

enveloped?

Answer 8

ssRNA +
(group 4)

Nonsegmented

icosahedral nucleocapsid

nonenveloped

(picornaviridae, enterovirus)

Question 9

What are the two characteristics of a virus that the baltimore classification system takes into account?

Answer 9

the type of nucleic acid it uses

the steps the nucleic acid takes to be replicated

Question 10

What are the 3 classes of DNA viruses?

Answer 10

1. 2. and 7.

1 - dsdNA with classical semiconservative replication

2 - ssDNA + with classical semiconservative replication, but you discard the negative strand when packaging

7 - dsDNA, but the mRNA is used as a template for reverse transcriptase to make genome copies to be packaged

Question 11

What do class 3 viruses have?

Answer 11

dsRNA

transcription of the minus strand gives mRNA for proteins

Question 12

What do class 4 viruses have?

Answer 12

ssRNA +

where the ssRNA+ is used directly for mRNA to translate proteins.

Question 13

What do class 5 viruses have?

Answer 13

ssRNA -

transcribe the minus strand to make mRNA

Question 14

What do class 6 viruses have?

Answer 14

they’re the retroviruses!

they have ssRNA + that is reverse transcribed to a dsDNA intermediate

the minu strand is then transcribed to make mRNA

Question 15

What determines the tropism for the virus?

Answer 15

what cells have the appropriate receptors the virus needs to bind and enter

Question 16

What are the 5 general steps in a viral infection?

Answer 16

after exposure….

1. attachment
2. penetration and absorption
3. synthesis
4. assembly
5. release

and then it continues in secondary infeections…

or you can do it this way…

1. pathogen exposure to mucosal surface
2. invasion
3. primary replication/imune reponse
4. dissemination
5. secondary infections
6. secondary replication and immune response
7. tissue destructoin
8. shedding

Question 17

What does HPV cause?

Answer 17

warts and carcinoma

Question 18

What are the characteristics of HPV?

genome/group

arrangement of genome

capsid shape?

enveloped?

Answer 18

dsDNA (group 1)

circular genome

icosahedral

nonenveloped

(papovaviridae, papillomavirus)

Question 19

How does HPV get the host cell to replicate?

Answer 19

It has two proteins - E6 and E7 - that will block p53 and Rb. Both of these would normally keep an infectec cell from entering S phase, but without them the cell will enter uncontrolled proliferation resulting in warts and carcinoma

Question 20

Describe the progression of HPV through the skin layers.

Answer 20

It enters the skin through a foriegn body or a microabrasion

In the lysogenic state it will infect basal cells and transform them using E6 and E7

In the lytic cycle the virus will either infeect the upper keratinized epithelium or it will just progress with the basal cell from below as it rises and differentiates

In the keratinized layer the virus is able to replicate its DNA and assemble new virions

Question 21

How does one diagnose HPV?

Answer 21

1% acetic acid will turn lesions white in colposcopy

you can then biopsy the white lesions or use PCR

Question 22

What strains of HPV does gardasil protect against?

Answer 22

6, 11, 16, and 18

Question 23

WHat are the general characteristics of poxviruses?

genome/group/arrangment

nucleocapsid?

envelope?

Answer 23

dsDNA (group 1)

linear genome

complex nucleocapsid

enveloped

Question 24

What is special about transmission of poxviruses?

Answer 24

can be zoonotic - form animals

Question 25

What does a complex nucleocapsid look like?

Answer 25

it's more of a barbell shape

Question 26

What are the 3 poxviruses we talk about?

Answer 26

molluscipoxvirus (mulluscum contagiosum) orthpoxvirus (smallpox) parapoxvirus (orf virus)

Question 27

What are the 4 herpesviruses we're interested in?

Answer 27

1. herpes simplex (HSV 1 and HSV2) 2. Herpes varicella (chicken pox) 3. Cytomegalovirus (CMV) 4. Lymphocyrptovirus (EBV)

Question 28

How are herpesviruses classified within the group?

Answer 28

alpha, beta, or gamma depending on where they survive in latency... alpha - in nerve cells (varicella and HSV) beta - in macrophages (CMV) gamma - in B cells (EBV)

Question 29

What are the general characteristics of herpesviruses? genome/group/arrangement? shape? enveloped?

Answer 29

dsDNA (group 1) linear icosahedral enveloped

Question 30

What does parvovirus B19 cause?

Answer 30

Fifth disease - erythema infectiosum also aplastic crisis (infection gets into bone marrow and kills precursor cells)

Question 31

WHat are the characteristics of parvovirus? genome/group/arrangement shape? enveloped?

Answer 31

ssDNA (group 2) linear genome icosahedral nonenveloped (parvoviridae, erythrovirus)

Question 32

Parvovirus is a biphasic disease, meaning...

Answer 32

has 2 phases... 1st phase: flue like symptoms with viral shedding during viremia 2nd phase: rash, arthralgia and arthritis. aplastic crisis

Question 33

What are the characteristics of picornaviruses? genome? segmented? shape? envelope?

Answer 33

ssRNA + (group 4) nonsegmented icosahedral nonenveloped (picornaviridae, enterovirus)

Question 34

What are the 5 picorna viruses we talk about?

Answer 34

1. poliovirus 2. coxsackievirus A and B 3. Echovirus 4. Rhinovirus 5. Enterovirus

Question 35

How are picornaviruses usually transmitted? What's the exception?

Answer 35

usually fecal-oral except the rhinoviruses which are respiratory droplets

Question 36

What are the characteristics of the measles virus (rubeola)? genome/group segmented shape enveloped?

Answer 36

ssRNA - (Group 5) nonsegmented helical enveloped (paramyxoviridae, morbillivirus)

Question 37

What is the pathogenicity of measles?q

Answer 37

1. infects epithelial cells of respiratory tract 2. spreads in lymphocytes and by viremia 3. replicates in conjunctiva, respiratory tract, urinary tract, lymphatics, blood vessels and CNS 4. T cell-response to the virus infected capillary endothelial cells causes the rash! (diffuse morbiliform) complications: otisi media, croup, bronchopneumonia, encephalitis, SSPE

Question 38

What are the characteristics of rubella (german measles)? geome/group semented? icosaheral enveloped?

Answer 38

ssRNA + (group 4) nosemgneted icosahedral enveloped (togavirus, rubivirus)

Question 39

What do you get with a rubella infection?

Answer 39

robeola - a rash

Question 40

What are the characteristics of flaviviruses? genome, group segmented? shape? envelope?

Answer 40

ssRNA + (group 4) nonsegmented icosahedral enveloped

Question 41

What are the two types of flaviviruses w talk about?

Answer 41

dengue fever and west nile

Question 42

How are flaviviruses transmitted?

Answer 42

moquitoes