Viruses are the most common cause of acute infections in humans
What are viruses?
• Obligate intracellular parasites
o They cannot perform metabolism on their own.
• Viruses are simple Darwinian machines. They survive because they make huge amount
of mutants. Selection removes the non-fittest.
• Many viral diseases can be viewed as a failure of the virus to adapt to its host.
The Origins of Virology
• A hieroglyphic found in 3700 BC, Memphis ancient Egypt. Typical clinical signs of
• Ramesses V’s preserved mummy shows that he died of smallpox at about the age of 35
in 1143 BC.
• The Chinese suffered from small pox in 1000 BC, China. They realized they can do
something about it. Variolation.
• 1519 A.D Smallpox was transferred from Europe to the Americas
• The Year 1796. Edward Jenner vaccinated a boy against smallpox boy, with material
from a cowpox lesion.
• The Year 1892. Dmitri Iwanowski, showed that extracts from diseased tobacco plants
can transmit disease to other plants by infectious agent smaller than a bacteria.
• The 1918 Spanish Flu