Introduction to viruses

Question 1

What was the first virus identified?

Answer 1

Yellow fever virus

Question 2

When was small pox introduced?

Answer 2

16th century to distinguish from great pox aka syphilis

Question 3

What causes smallpox?

Answer 3

variola virus

Question 4

What kind of virus is variola virus?

Answer 4

A poxvirus

Question 5

What is so significant about smallpox?

Answer 5

It was the first disease successfully eradicated by vaccination

Question 6

How many people did Spanish Flu kill?

Answer 6

> 50 million people

Question 7

Why is it difficult to control pandemic influenza?

Answer 7

New strains continuously emerging

Question 8

What cancer was HIV associated with?

Answer 8

Kaposi’s sarcoma

Question 9

Are new emergences of viruses rare events?

Answer 9

No, new viruses emerge regularly

Question 10

What is MERS?

Answer 10

Middle East Respiratory Syndrome, a new coronavirus disease that emerged in 2012 and by 2015 it had disseminated to 27 different countries

Question 11

How fatal is MERS?

Answer 11

Fatal in 50% of infected

Question 12

What was the origin of MERS?

Answer 12

Camel to human transmission

Question 13

What is the host range of viruses determined by?

Answer 13

Virus requirements for attachment to host cell

Availability of host cell factors required by virus to replicate

Ability of virus to evade host defences

Question 14

Can viruses cross species barriers?

Answer 14

Yes and they frequently do

Question 15

How does mode of infection determine clinical outcome?

Answer 15

The cells which can be infected will determine what is damaged. (Eg. HIV attaches to CD4 so it can only infect CD4 T cells)

Question 16

How does influenza virus A infect people?

Answer 16

It attaches to sialic acid on epithelial cells

Question 17

What is the structure of a virus?

Answer 17

3 main parts:

Nucleic acid (DNA or RNA)

Protein coat (capsid)

Lipid membrane (envelope)

Question 18

Are all viruses enveloped?

Answer 18

No

Question 19

What is a virion?

Answer 19

A single virus particle

Infectious and fully developed

Question 20

What type of structures can the viral nucleic acids be?

Answer 20

DNA or RNA

Single or double stranded

Linear or circular

Can be segmented

Size ranges from a few thousand nt to 250k or more

Question 21

How many nts can giant viruses have?

Answer 21

1m+

Question 22

What are some examples of giant viruses?

Answer 22

Mimivirus

Pandoravirus

Question 23

What is a capsid?

Answer 23

A protein coat that surrounds the nucleic acid

Question 24

What is the capsid used for?

Answer 24

It is a vehicle for transport and proteiction

Question 25

What makes up most of the mass of the virus?

Answer 25

The capsid

Question 26

What is a capsid made up of?

Answer 26

Repeated subunits called capsomeres.

Question 27

What are capsomeres made up of?

Answer 27

Single or several protein types. Arrangement is characteristic for the particular virus

Question 28

What are the types of viral morphologies that are possible?

Answer 28

Helical viruses Icosahedral viruses Complex

Question 29

What are helical viruses like structurally?

Answer 29

Rigid or flexible Nucleic acid within hollow cylindrical, helical capsid Spiral arrangement of capsomers around nucleic acid

Question 30

What are some examples of helical viruses?

Answer 30

Ebola Influenza

Question 31

When was helical symmetry of viruses first described?

Answer 31

1955 by Fraenkal, Conrat and Williams

Question 32

How are icosahedral viruses formed?

Answer 32

Capsomers assemble into 20 equilateral triangular faces

Question 33

What can regular complex viruses look like?

Answer 33

Capsids can have both helical and icosahedral symmetry. Additional structures can also be present such as the capsid (polyhedral) and the sheath (helical) Think of bacteriophages to understand this better

Question 34

What can irregular complex viruses look like?

Answer 34

Non-symmetrical capsid structure (eg pox viruses) They lack clearly identifiable capsids Several coats can be present around the nucleic acids

Question 35

What can envelope of virus be used for?

Answer 35

To group viruses

Question 36

What are viral envelopes made of?

Answer 36

Outer lipid membrane derived from host membrane and contains viral proteins.

Question 37

What does the viral envelope do?

Answer 37

Mediates viral attachment to host cells for cell entry

Question 38

What structures do enveloped viruses usually have?

Answer 38

Helical or icosahedral

Question 39

How are viruses seen?

Answer 39

EM

Question 40

How small are viruses?

Answer 40

100 times smaller than a single bacterial cell

Question 41

What did mimivirus resemble when it was first discovered?

Answer 41

Gram positive bacteria residing within amoeba

Question 42

How does sputnik replicate itself if it cannot replicate in acanthamoeba by itself?

Answer 42

It uses the machinery of another virus called mamvirus to replicate itself.

Question 43

What are the ways viruses are classified?

Answer 43

Orders (-virales) Families (-viridae) Genera (-virus) Species

Question 44

How are viruses grouped into families?

Answer 44

Morphology Nucleic acid type (RNA or DNA) Strategy of replication

Question 45

What are the criteria for grouping viruses into genera?

Answer 45

Primary criteria: Significant differences in genome sequence Minor difference in genome structure Type species: virus which has all the properties characteristic of a certain genus

Question 46

What are the criteria for grouping viruses into a certain species?

Answer 46

Separate species associated with serological differences, genomic differences, and structural + physical properties.

Question 47

What is a species when talking about viruses?

Answer 47

Defined as class of viruses with many properties that constitutes a replicating lineage and occupies a particular ecological niche

Question 48

How are new species of virus created?

Answer 48

Variant species arise as a result of minor mutations in genome

Question 49

How are species subgrouped?

Answer 49

Subtypes Clades Strains Variants Quasispecies

Question 50

What are prions?

Answer 50

Non-viral proteins that cause disease. (eg spongiform encephalopathy)

Question 51

What diseases are caused by prions?

Answer 51

Chronic wasting disease in deer Mad cow disease Cruetzfeldt-Jakob disease in humans (vCJD) Kuru - first identifiable spongiform encephalopathy

Question 52

Where are prions typically located?

Answer 52

In nervous tissue

Question 53

What do prions do?

Answer 53

Convert glycoprotein PrP(c) to PrP(Sc) [misfolds the protein]

Question 54

How is mad cow disease transmissible?

Answer 54

Surgical instruments Orally: via consumption of infected meat/nervous tissue