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Flashcards in Biology of Viruses Deck (16)

What is unique about negative RNA?

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.


What is an indication of acute viral infection?

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


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

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


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

Interferon leads to inhibition of protein synthesis and virus replication


Lytic Infection

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


Latent Infection

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).


Persistent Infection

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.


Cytopathic Effect

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


What genome are Picornaviradae?

Single strand positive RNA


What is the transmission of Picornaviradae?

Fecal-oral - except for Rhinovirus


What is the pathogenesis of poliovirus?

- 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


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

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.


Salk vaccine

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


Sabin vaccine

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


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

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


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

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

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