Transcript “Ancient” Viruses

Virology
 Virology
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is defined as the study of viruses.
But it involves more than just viruses.
What are the characteristics of
viruses?
• Pathogenic
• Small
• Non-living
• Parasitic
Derivation of the name
for “poison”
 Later used interchangeably for all
infectious agents
Became restricted to modern usage much
later-when every other pathogen had its
own name
Viruses were discovered last and kept the
old name
 Originally-Latin
“Ancient” Viruses
Virus Discovery Timeline
 1880s:
Adolf Mayer
discovers filtrable TMV
agent-used “candle”
filters
 1898:
Dmitry
Iwanofsky confirms
discovery
Virus Discovery Timeline
 1898:
Martinus Beijerinck realized a new
form of disease agent was involved
 1898: Loeffler and
Frosch identify
FMD agent as
a virus
 1901: Walter
Reed and others
study yellow fever
in Cuba
Criteria for Distinguishing Among
Viruses, Bacteria and Toxins
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Growth in vitro
Filtrable
Increase in vivo
Visible with light
microscope
Operational definition
Bacteria
Toxin
Virus
yes
no
yes
no
yes
no
no
yes
yes
yes
no
no
Hosts for viruses
 Plants-e.g.
tobacco for TMV
 Animals-e.g. humans for poliovirus or
smallpoxvirus or insects for nuclear
polyhedrosis virus
 Bacteria-e.g. bacteriophage lambda
 Fungi-e.g. cryptoviruses
 Your book does not do a good job on nonhuman viruses
Smallpox Eradicated
20th Century Epidemic
“Broken” tulips
Bacteriophage plaques
Viruses are Abundant
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Culture-independent methods such as microscopy or
PCR used
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Virus count varies with habitat
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3-100 million viruses per ml
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Further reading: Nature 437, 356-361 (15 September
2005) Viruses in the sea by Curtis A. Suttle
Viruses in Global Ecology
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PARIS -- Scientists on Wednesday said they had discovered deep-sea
viruses to be an unexpectedly potent driver.
of the so-called carbon cycle that sustains oceanic life and helps dampen
global warming.
Under the carbon cycle, microscopic algae at the sea surface suck up
carbon dioxide from the atmosphere.
Many of these prokaryotes, become infected by naturally-occurring marine
viruses.
When they die, their carbon-rich remains gently sink to lower depths, where
they are then cannibalistically gobbled up by other bacteria.
These prokaryotes in turn become a meal for a larger life form and so on,
up the food chain.
Researchers long ago grasped that viruses on the sea surface play a Dr.Jekyll-and-Mr.-Hyde role, killing biomass while at the same time sustaining
it.
Viruses in the lab
The ability to carry genes from cell to cell is
very useful
“Vectors” in genetic engineering and gene
therapy
The word “vector” has two meanings in
virology
Either a an animal that carries a disease or
a virus that is carrying a gene of interest in
an experiment or in gene therapy
Viruses in evolution
As agents of evolution via transduction
Remnants from an ancient and promiscuous
gene pool?