Virology

Question 1

Describe the structure of a virus.

Answer 1

1. ) Nucleic acid (could be DNA or RNA)
2. ) Surrounded by a protein coat (capsid)
3. ) Lipid envelope (sometimes.

Question 2

What is a capsid? What are its components?

Answer 2

Capsid is the protein shell that encases viral nucleic acid. It is composed of capsomeres held together by non-covalent bonds.

Question 3

What is the envelope of a virus composed of and from where does it originate?

Answer 3

The envelope is usually composed of a lipid bilayer with glycoproteins present on the surface.

It’s derived from the host cell.

Question 4

Pleomorphism

Answer 4

The ability of some viruses to alter their shape or size

Question 5

Identify and describe the steps in the replication cycle of a virus.

Answer 5

1. Attachment - virus attaches to host cell.
2. Penetration - Virus penetrates the cell membrane of the host cell.
3. Uncoating - the virus injects its nucleic acid into the host cell (not the capsid).
4. Synthesis of viral nucleic acid and protein
5. Assembly and maturation
6. Release in large numbers - this usually results in death of the host cell.

Question 6

What are the impacts of viral replication on the host cell (4).

Answer 6

1. ) Cell death (via lysis, alteration in cell membrane, apoptosis).
2. ) No apparent change - latent, persistent or chronic infection
3. ) Transformation of cell to malignant cell.
4. ) Fusion of cells forming multinucleate and later hybrid cells (after mitosis).

Question 7

What is ICTV?

Answer 7

International Committee on Taxonomy of Viruses (ICTV) is the only body charged by the International Union of Microbiological Societies with the task of developing, refining, and maintaining a universal virus taxonomy.

Question 8

What considerations are made when classifying viruses?

Answer 8

1. ) Nature of the virus genome and virus genetic diversity
2. ) Virus replication strategies
3. ) Virus morphology.

Question 9

Describe serial passage of viruses to create live-attenuated virus vaccines.

Answer 9

This involved placing the virulent virus in an environment it will survive, but not thrive. Collecting it from that environment and placing it into a new environment in which it will survive, but not thrive. After repeating the process several times, the bacteria will mutate for its own survival and those mutations also end up reducing virulence its original host acting as a vaccine rather than a pathogen.

Question 10

What are non-replicating virus vaccines?

Answer 10

Vaccines produced from inactivated viruses OR parts of viruses.

Question 11

What are recombinant vaccines?

Answer 11

Vaccines produced by either mutating the virus so it’s genetic composition is severely altered OR subunit vaccines in which a small chunk of viral protein or nucleic acid is introduced to the host. This alerts the immune system with an idea of what the pathogen looks like without risking virulence.

Question 12

Define pathogenicity

Answer 12

the ability of a virus to cause disease in a host

Question 13

Define pathogeneis

Answer 13

the mechanism of development of a disease

Question 14

Define virulence

Answer 14

a measure of the degree of pathogenicity of the infecting virus

Question 15

Define Lethal Dose (LD50).

Answer 15

The dose of the virus required to cause death in 50% of animals.

Question 16

Define Primary Viremia

Answer 16

Initial entry of virus into the blood. This may occur by the spread of infection into the blood or direct injection into the blood via arthropods, needles, etc.

Question 17

Define Secondary Viremia.

Answer 17

Virus has replicated/multiplied in major organs and once more entered the circulation.

Question 18

Define Disseminated Infection

Answer 18

Infection spreads beyond the primary site of infection

Question 19

Define systemic infection.

Answer 19

a number of organs or tissues are infected.

Question 20

Define neurotropic virus

Answer 20

viruses that can infect neural cells. (Infection may occur by neural or hematogenous spread

Question 21

Define neuroinvasive virus

Answer 21

viruses that enter the CNS after infection at a periopheral site

Question 22

Define Neurovirulent virus

Answer 22

viruses that cause dz of nervous tissue, manifested by neurological symptoms and often death.

Question 23

What role do trafficking monocytes play in viral infections?

Answer 23

They can transport viruses - especially when crossing the blood-brain barrier.

Question 24

Define tropism.

Answer 24

The specificity of a virus to a particular host tissue.

Question 25

Define pantropic virus

Answer 25

Viruses that are able to replicate in more than one host organ/tissue.

Question 26

Define oncovirus.

Answer 26

A virus that causes cancer.

Question 27

What is infectious bursal disease?

Answer 27

A virus in birds in which viral replication causes atrophy of the bursa and a severe deficiency of B lymphocytes, resulting in immunosupression. (immunosuppression is a potential outcome of viral injury).

Question 28

What is DIC?

Answer 28

Disseminated Intravascular Coagulation: widespread activation of clotting mechanism first leads to small blood clots throughout the body. This eventually leads to severe bleeding because all clotting factors have been used up.

Question 29

What is immune-complex formation?

Answer 29

The complex is comprised of antigen-antibody complex. The antibody is inefficient and binds to the antigen without neutralizing it. Antibodies continue to bind to antigens forming clumps of antigen-antibody complexes which can cause these complexes to deposit in the blood vessels and cause vasculitis.

Question 30

Define teratogenic virus

Answer 30

A virus that causes developmental defects of embryo or fetus after in-utero infection.