2- Classification and Replication

Question 1

What is a prion?

Answer 1

Not a virus, or any other recognized infectious agent
- it is a misfolded protein

Question 2

What is the purpose of the capsid and envelope (when present)?

Answer 2

Serve to protect the genome (DNA &RNA)

Question 3

What are the components of a virus?

Answer 3

• nuclei acid core
• capsid (an outer glycoprotein coating)
• an outer envelope (sometimes)

Question 4

The function of the capsid is to protect the fragile nucleic acid genome from:

Answer 4

• physical damage: shearing my mechanical forces
• chemical damage: UV irritation leading to chemical modification
• enzymatic damage: nucleases derived from dead or leaky cells or deliberately secreted by vertebrates as defense against infection

Question 5

List some properties of viruses that are important relative to disinfection and transmission

Answer 5

• heat sensitivity
• pH sensitivity
• lipid solvents
• chemicals
• radiation and UV light
• humidity

Question 6

What are the two types of symmetric viral structure?

Answer 6

Isometric (icosahedral): constructed of 20 equilateral triangular faces
Helical: tubular construction with the subunits arranged around the nucleic acid in a coil

Question 7

What are the two viral structures with no recognized symmetry?

Answer 7

Complex (looks like a little rocket)
Filamentous (Ebola, looks like Mickey mouse with a tail)

Question 8

Viral taxonomy is based upon what 4 characteristics?

Answer 8

• morphology of iron, capsid, and envelope
• genome (RNA, DNA, SS, DS etc)
• serological relationships (stereotypes)
• replication strategy

Question 9

What are some characteristics of structural proteins in a virus

Answer 9

• important for viral stability and attachment
• antibodies are generally formed against the structural proteins

Question 10

What are some characteristics of non-structural proteins in a virus

Answer 10

• enzymes involved in viral replication
• when antibodies are found against the non-structural proteins this may help in differentiating animals vaccinated with inactivated recombinant vaccines from those naturally infected (DIVA principle)

Question 11

The capsid and envelope of the virus is responsible for what?

Answer 11

Recognition of the host cell (Receptor binding)

Question 12

Differentiate between promiscuous and plastic

Answer 12

• promiscuous: capable of infecting several species
• plastic: exhibiting adaptability to change or variety in the environment

Question 13

A well characterized virus is known as a ______.

Answer 13

Strain

Question 14

Different strains may have different properties, such as ______.

Answer 14

Virulence

Question 15

An ____ refers to the virus recovered from a specific host or location

Answer 15

Isolate

Question 16

________ generally means that immunity is not conferred by previous exposure to a different type

Answer 16

Serotype

Question 17

How are enteric viruses acquired?

Answer 17

By ingestion (fecal-oral transmission) and replicate primarily in the intestinal tract

Question 18

How are respiratory viruses acquired?

Answer 18

Acquired by inhalation or fomites (inanimate objects carrying virus contagion) and replicate primarily in the respiratory tract

Question 19

How are arboviruses transmitted?

Answer 19

Replicate in their hematophagous (blood-feeding) arthropod hosts and are then transmitted by bite to vertebrate hosts

Question 20

How are oncogenic viruses transmitted?

Answer 20

Acquired by close contact, injection fomites, and unknown means

Question 21

What are the steps of virus replication

Answer 21

Attachment
Penetration
Uncoating
Transcription
Translation
Replication
Assembly (maturation)
Release