week 9 - viruses classification, discovery + disease

Question 1

what is a virus

Answer 1

• A virus is an infectious obligate (need to take things from host cells) intracellular parasite
• Obligate intracellular: must enter a host cell to reproduce more viruses
• Parasite: relies on the host for reproduction (materials and energy

Question 2

virus
genome

Answer 2

• Genome composed of DNA and RNA
  o Serves as he template to make new viral components using cell systems
  o Viruses only known things to use RNA for genetic material (ancient origins)

Question 3

virus
protein coat

Answer 3

• Protein coat surrounds genome
  o Capsid or core
  o Protects viral genome during cell-to-cell and host-to-host transmission

Question 4

virus
membrane?

Answer 4

• Some viruses have a membrane
  o Contains spike glycoproteins

Question 5

virus:
classification
4 criteria

Answer 5

• DNA or RNA
• Symmetry of capsid
• Enveloped or not
• Dimensions

Question 6

virus:
classification
genome (7 virus genome types)

Answer 6

dsDNA
ssDNA
dsRNA
(+)RNA
(-)RNA
(+)RNA (RT)
dsDNA (RT)

Nature (DNA vs RNA) and polarity
Steps required to make mRNA
Dna –> split the copy

Rna –> need to make double strand in order to copy it
* Host cells have opportunity to stop
When have an RNA DNA hybrid
* More stable

Question 7

VIRUS DISCOVERY:
concept of microorganisms
Koch’s postulates

Answer 7

1. The microorganisms must be found in diseased but not healthy individuals
2. The microorganism must be cultured from the diseased individual
3. Inoculation of a healthy individual with the cultured microorganisms must recapitulated the disease
4. The microorganism mist be re-isolated from the inoculated diseased individual and matched to the original organism

Question 8

VIRUS DISCOVERY:
concept of microorganisms
Pastteur (1861)

Answer 8

• Term virus was used a searly as 1728 to describe an agent of infectious disease
• Virus in Latin means poison
• Pasteur “every virus is a microbe” he assumed viruses were very small bacteria

Question 9

VIRUS DISCOVERY:
concept of microorganisms
turning point

Answer 9

(before this viruses just moving through filters)
* Development of Chamberland filter (1884)
* Porcelain filter
* Allowed for the removal od bacteria from drinking water
* Allowed for the discovery of bacterial toxins (Diptheria and tetanus toxin)

Question 10

VIRUS DISCOVERY:
concept of microorganisms
First plant virus

Answer 10

Tobacco mosaic virus
* 1892 Ivanovsky and Beijernick
* Show that the virus that passes through a Chamberland filter can infect a healthy plant
* Transmissible
* Key concept:
o Too small to be bacteria (pass through 02uM filter)
o Everyone still thinks “viruses” are liquid

Question 11

VIRUS DISCOVERY:
concept of microorganisms
first animal virus

Answer 11

foot and mouth disease
* 1989 Loeffelr and Frosch
* Show that the “virus” that passes through a Chamberland Filter is infectious
* Key concept
o Agent does not replicate in brother but only in a new host

Question 12

VIRUS DISCOVERY:
concept of microorganisms
dates: viruses still considered infectious liquids

Answer 12

1901 - first human virus (yellow fever virus)
1903 - rabies virus (Pasteur)
1906 - small pox virus (Variola)
1908 - polio virus
1915 - bacteria phage
1933 - influenza virus

viruses still considered infectious liquids

Question 13

VIRUS DISCOVERY:
concept of microorganisms
dates: technological advance

Answer 13

1939: technological advance shows that viruses as particles

1933: Helmut Ruska built the first electron microscope

Finally 1939: the first virus (bacteriophage) seen

The word filterable is dropped as viruses as particles (not liquid)
* Drives the birth pf virology as a field of study

1942: first animal virus visulised Vaccina virus (smallpox vaccine)
* Vaccina becomes first virus to be grown in tissue culture
* First virus purified
* First virus chemically analyzed

Question 14

VIRUS DISCOVERY:
what do we know?

Answer 14

We have molecular details of virus structure (crystallography and cryo-electron microscopy)
* Genomic and transcriptomic sequencing has been a hige breakthrough in virus discovery (not driven by disease discovery anymore)

Estimates only 1% of virus diversity have been identified

Transcriptome analysis of 1,243 species of incest revealed novel viral genera in seven families identifying over 488 RNA polymerase genes

SarS CoV2 was first identified by sequencing and classed as a novel Coronavirus based on similarity

Question 15

VIRUSES AND DISEASE
overview

Answer 15

• Viruses are all around us
  o We breathe, eat and host billions of virus particles
• Viruses can infect all living things
  o Humans, animals (pets and wildlife) plants, insects, bacteria (page)
• There are 10^300 bacteriophage in the oceans
• We ingest a vast amount (billions) of non-animal viruses in our food
• We are chronically infected by a range of herpes viruses by age 10
  o HSV1, HSV2, VZV (chickenpox), HCMV see slides

Question 16

VIRUSES AND DISEASE
human impact

Answer 16

The vast majority of viruses that exist and infect us have little to no impact on human health and disease

Viruses are part of us
* They make up a portion of our genetic information
o Endogenous retroviruses make up 5-8% of our DNA

Question 17

VIRUSES AND DISEASE
beneficial?

Answer 17

• Mammalian placental fusion is driven by an endogenous defective retrovirus fusion protein
• Syncytia is a captive retroviral envelope protein involved in human placental morphogenesis

Question 18

VIRUSES AND DISEASE
how do we survive all these viral assaults

Answer 18

• many viruses pass right through (don’t replicate)
  o Cell Receptors
• Many replicate but don’t cause pathology
  o Don’t cause disease (don’t destroy host cell)
• We have an outstanding immune system
  o Keeps invading virus in check
  o Keeps chronic viruses in check
  o Problems: immunocompromised,, immunorepressed

Question 19

VIRUSES AND DISEASE
mortality

Answer 19

Viruses remain a major global cause of morbidity and mortality
* Top 3/4
“the single biggest threat to man’s continued domination of the planet is the virus”
* Joshua Lederberg PhD, Nobel Laureate
o Referring to emerging viral haemorrhagic fevers:
* Hantan, Ebola, Marburg, Lassa fever

Question 20

VIRUSES AND DISEASE
anti-viral drugs

Answer 20

Need more anti-viral drugs
More vaccines for existing and new

Question 21

viruses summary:
viruses are…

Answer 21

infectious, obligate intracellular microorganisms

Question 22

viruses summary:
viruses can be distinguished from other microorganisms by…

Answer 22

size and host requirements

Question 23

viruses summary:
viruses are relatively…

Answer 23

new on the time-line of microorganism discovery (driven by technological advances)

Question 24

viruses summary:
viruses infect…

Answer 24

everything, and they are part of us

Question 25

viruses summary:
most viruses do not…

Answer 25

impact human health

Question 26

viruses summary:
viruses that impact human health can be…

Answer 26

devestating

Question 27

viruses summary:
viruses have always been and will continue to be a….

Answer 27

a major player in human health and shaping populations