Lecture 15: Introduction to Viruses

Tobacco Mosaic Virus was identified in the 1930s.
Viral diseases such as rabies have affected humans for many centuries.
The first written record of a virus infection is shown in hieroglyphs from Memphis, drawn in approximately 3700BC, which depicts a temple priest called (Ruma) showing typical clinical signs of paralytic poliomyelitis.
Pharaoh Ramses V (died 1196 BC) had Pox marks on mummy suggests he may have died from Smallpox
In the late 18th century, Edward Jenner observed a milkmaid who had previously caught Cowpox and was subsequently found to be immune to Smallpox.
May 1796, Jenner used cowpox-infected material obtained from the hand of the milkmaid to successfully vaccinate an 8-year-old boy.
July 1796, Jenner challenged the boy by deliberately inoculating him with material from a real case of smallpox. The boy did not become infected!

Demonstrated that extracts from infected tobacco plants could transmit disease to other tobacco plants
Filtering extract with Chamberland filter, a porcelain filter developed by Chamberland to remove bacteria from drinking water, did not prevent transmission
Postulated that there was a novel “very small” infectious agent much smaller than bacteria

Confirmed the same findings and showed that the filtrate contained a new form of infectious agents.
Demonstrated that the agent multiplied only in living dividing cells because filtrate retained infectivity even after dilution.
He called it a contagium vivum fluidum (soluble living germ) and used the term filtrable agent to describe it (considered the father of virology).
- Diluted filtrate 1/10, 1/100, 1/1000 sprayed onto healthy Tobacco leaves all caused infection

Repeated the TMV experiments and demonstrated Foot and Mouth Disease in cattle was caused by similarly small infectious agents, Foot and Mouth Disease Virus (FMDV) (picornavirus family)

A Cuban physician, first conducted and published research that indicated that mosquitoes were carrying the cause of yellow fever.
So, the first human virus to be identified was the yellow fever virus.

Phages were first mentioned in 1915 by an English doctor called Frederick Twort
He described how a phage infection of Staph gave rise to clear zones of lysis as phages appeared to destroy the bacteria.
In 1917, the French Canadian microbiologist, Félix d’Herelle was first to isolate Phages.
He described them as bacteriophage (as they ‘eat’ bacteria).

Disease
- CORONAVIRUS DISEASE 2019 (COVID-19)
- Smallpox
- ZIKA VIRUS
- HIV
- Hepatitis
- Poliomyelitis
- Influenza
- Cervical cancer
- Viral Disease
  - Human Papilloma Virus
  - Polio virus
  - Coronavirus
  - Smallpox
  - Influenza
  - Ebola
  - Zika virus
  - HIV
  - Hepatitis B virus (HBV)
Therapeutics
- Gene delivery
- Targeted therapy
- Gene editing
Technology
- siRNA
- Detection
- Novel therapies
- Virus like particles
- CRISPR
Vaccines
*Antiviral Drugs
*Understanding the Viral Life Cycle Allows Development of Antiviral Drugs

Capsid
RNA
Envelope (with glycoproteins)
Glycoproteins on the viral envelope bind to specific receptor molecules on the host cell, promoting viral entry into the cell.
The capsid and viral genome enter the cell. Digestion of the capsid by cellular enzymes releases the viral genome.
Complementary RNA strands also function as mRNA, which is translated into both capsid proteins (in the cytosol) and glycoproteins for the viral envelope (in the ER and Golgi apparatus).
Vesicles transport envelope glycoproteins to the plasma membrane.
A capsid assembles around each viral genome molecule.
New copies of viral genome RNA are made using complementary RNA strands as templates.
Each new virus buds from the cell, its envelope studded with viral glycoproteins embedded in membrane derived from the host cell.