Biology of Viruses

Question 1

What is unique about negative RNA?

Answer 1

RNA of negative polarity cannot be translated directly into protein. The RNA must first be transcribed into mRNA. This process creates a complimentary strand of RNA, called positive RNA, which can be translated into protein.

Question 2

What is an indication of acute viral infection?

Answer 2

Detection of IgM specific to the virus during the acute stage of illness is frequently used in diagnosis.

Question 3

What is an indication of the convalescent stage of viral infection?

Answer 3

Detection of IgG specific to the virus is a good indicator of previous exposure to the virus.

Question 4

What is the ultimate function of interferon in host defense against viruses?

Answer 4

Interferon leads to inhibition of protein synthesis and virus replication

Question 5

Lytic Infection

Answer 5

The cell acts as a factory for virus replication. Hundreds to thousands of virus particles are produced and the cell dies.

Question 6

Latent Infection

Answer 6

The viral nucleic acid resides in the cell as either an extrachromosomal element (herpesviruses) or becomes integrated into the host cell chromosome (retroviruses). This can lead to important consequences if the viral genetic information is reactivated. Reactivation can lead to recurrence of disease (herpes) or may result in transformation of the cell (retroviruses).

Question 7

Persistent Infection

Answer 7

Characterized by a continual shed of virus particles after the acute illness has passed. The amount of virus produced is generally lower than in lytic infections and virus production does not kill the host cell.

Question 8

Cytopathic Effect

Answer 8

A recognizable cytopathic effect (CPE) is obtained through the killing of cells by some viruses. Different cells produce different cytopathic effects:

•  cell lysis
•  cell fusion (syncytia)
•  vacuolation

Question 9

What genome are Picornaviradae?

Answer 9

Single strand positive RNA

Question 10

What is the transmission of Picornaviradae?

Answer 10

Fecal-oral - except for Rhinovirus

Question 11

What is the pathogenesis of poliovirus?

Answer 11

•  Poliovirus enters via the intestinal mucosa and infects the underlying lymphatic tissue.
•  In the absence of serum antibody, poliovirus spreads by viremia to cells of a receptor-bearing target tissue.
•  The infected target tissue determines the subsequent disease

Question 12

What is the most severe consequence of poliovirus and how is it caused?

Answer 12

Paralytic Polio.

The virus spreads from the blood to the anterior horn cells of the spinal cord and the motor cortex of the brain. The severity of the paralysis is determined by the extent of the neuronal infection and the neurons affected.

Question 13

Salk vaccine

Answer 13

Contains inactivated poliovirus of all three serotypes. The vaccine was given intramuscularly and little or no duodenal IgA was generated.

Question 14

Sabin vaccine

Answer 14

Live, attenuated vaccine of all three serotypes. It is given orally and induces good duodenal IgA response.

Question 15

What is the risk of the Sabin (oral) polio vaccine?

Answer 15

Paralytic poliomyelitis that is more likely in immunodeficient persons. For this reason, the IPV is preferred over the OPV.

Question 16

The mechanism of action of interferon involves:

A. Induction of enzymes to degrade mRNA and inhibit protein synthesis
B. Upregulation of the immune response to viral antigens
C. Stimulation of the cycle to cause cells to divide before they are infected
D. Shutdown of splicing activity in the virus infected cells.
E. Killing of virus infected cells by NK cells

Answer 16

A. Induction of enzymes to degrade mRNA and inhibit protein synthesis