Introduction to Viruses

Question 1

What are viruses made of?

Answer 1

Inside to Outside:

• Nucleic Acid Genome
• Capsid Protein Shell
• Possible Envelope

Question 2

Why were polio+smallpox eradicated but influenza wasn’t?

Answer 2

Polio+Smallpox
-narrow tropism, limited # of strains, good vaccine

Influenza
-Broad tropism and large number of strains

Question 3

What occurred in 1918-1919?

Answer 3

Spanish Flu

-30 million people dead

Question 4

Who were the three responsible for the discovery of the first viruses? What was the significance?

Answer 4

Ivanosky (1892)
-observed that the causative agent of Tobacco Mosaic Virus (TMV) wasn’t retained in filters that captured bacteria

Beijerinck (1896)
-concluded the causative agent must be distinct from bacteria and small enough to pass thru filter

Loeffler & Frosch (1898)
-observed causative agent of foot and mouth disease was also filterable

These agents passed through filters and were able to replicate and cause disease in host

Question 5

What were the first three viruses discovered?

Answer 5

Yellow fever virus (1901)
-first discovered, by Walter Reed

Bacteriophages (1915)

Influenzavirus (1933)

• Infected ferrets w/ throat washings of sick ppl
• virus replicated and researchers able to isolate

Question 6

What enabled scientists to view viruses for the first time?

Answer 6

Electron microscope

Question 7

What are viruses?

Answer 7

Very Small infectious particles consisting of nucleic acid enclosed in a protein coat and in some cases a membranous envelope

Question 8

What is the order, from smallest to largest, of an animal cell virion (viral cell) and a bacterial cell?

Answer 8

Virion < Bacterial Cell< Animal Cell

Question 9

What do viral genomes consist of?

Answer 9

Double or single stranded DNA
-dsDNA or ssDNA

Double or single stranded RNA
-dsRNA or ssRNA

The type of nucleic acid in genome determines its classification

Question 10

What are the definitive properties of viruses?

Answer 10

1. small, infectious, obligate intracellular parasite
2. viral genome either DNA or RNA
3. inside host, viral genome is replicated. genome also directs synthesis of other viral components by using host systems
4. progeny virions are formed by de novo assembly from newly synthesized components within the host cell
5. progeny virion is the vehicle for transmission of viral genome to next host cell

Question 11

How do viruses enter the cell?

Answer 11

Endocytosis
-host cell takes up virion

Direct fusion
-plasma membrane of cell and viral membrane mix and empty contents into host cytoplasm

Question 12

Where do most DNA and RNA viruses have to get in order to replicate?

Answer 12

MOST DNA viruses:
-have to get their DNA into Host Nucleus

MOST RNA viruses:
-have to replicate genome in host cytoplasm

Question 13

What are disease reservoirs?

Answer 13

Places where pathogens live, grow, replicate

Animate reservoirs
-Animals

Inanimate reservoirs
-contaminated food, water and surfaces

Question 14

Why does Dr. Frampton call influenza a hit+run virus?

Answer 14

Acute and doesn’t stick around long because it’s cleared by the body

Has to find next host quickly

Question 15

What is the difference between emerging and re-emerging diseases?

Answer 15

Emerging Disease
-certain population has not experienced this pathogen

Re-emerging Disease
-gone but came back

Question 16

How is west nile virus transmitted?

Answer 16

From bird to mosquito to Humans & Horses

Question 17

How do we fight back against viruses?

Answer 17

Vaccines

• prevent certain viral illnesses
• viral infections CANNOT be treated w/ antibiotics

Antiviral Drugs
-can help to treat but not cure viral infections

Question 18

What are the types of traditional vaccines?

Answer 18

Killed or inactivated vaccines

Live, attenuated (weakened) viruses

Question 19

What is the newer generation vaccine?

Answer 19

Made using recombinant DNA methods

-usually safer (parts not the whole virus)

Question 20

What kind of virus is HIV?

Answer 20

An RNA Retrovirus

• uses Reverse Transcriptase (RNA->DNA)
• uses Integrase to integrate its DNA into host DNA

Question 21

How are viruses used for good?

Answer 21

Used as vectors in Gene Therapy

Used in phage therapy

• bacteriophages used to combat bacterial infections
• MRSA

Question 22

What are the three funamental properties of viral propagation?

Answer 22

1. All viral genomes are packaged inside particle that mediate their transmission from host to host
2. Viral genome contains the info for initiating and completing an infectious cycle in host
3. All viruses are able to establish themselves in a host population so that virus survival is ensured

Question 23

What are the general features of viral reproductive cycles?

Answer 23

Viruses enter cells by various mechanisms

Once a viral genome has entered cell, the cell begins to manufacture viral proteins

The Virus makes use of host enzymes, ribosomes, tRNAs, amino acids, ATP and other molecules

Viral nucleic acid molecules (RNA or DNA) and capsomeres spontaneously self assemble into new viruses