History of Viruses and Vaccination

History of Viruses

• Earliest written record of a virus infection dates back to approximately 3700 BC.
• A hieroglyph from Memphis, Egypt, depicts a priest, Ruma, exhibiting signs of paralytic poliomyelitis.
• In 1196 BC, Ramesses V, died of smallpox at around age 35.
• Smallpox was endemic in China by 1000 BC.
• Survivors of smallpox outbreaks were found to be protected.
• Variolation involved inhaling dried smallpox lesion crusts or, later, inoculating the pus into a scratch on a child's forearm.

Edward Jenner

• In the late 18th century, Edward Jenner observed a milkmaid, Sarah Nelmes, who had previously contracted cowpox and was subsequently immune to smallpox.
• On May 14, 1796, Jenner used cowpox material from Sarah Nelmes to successfully vaccinate an eight-year-old boy, James Phipps, against smallpox.
• Jenner's work led to the development of the first vaccine, and smallpox has been largely eradicated.

Koch's Postulates and Germ Theory

• Koch's postulates outline criteria for establishing a link between a microorganism and a disease: the agent must be present in every case, isolated from the host, and reproducing the disease when inoculated into a healthy host, and the same agent recovered.
• The germ theory of disease, jointly proposed by Robert Koch and Louis Pasteur in the 1880s, emphasized the role of microorganisms in causing diseases.

Filterable Agents

• In the late 19th century, Charles Chamberland developed a porcelain filter for virology research.
• Dimitri Ivanovski used this to study the tobacco mosaic virus, showing infectious agents smaller than bacteria.
• This work proved that viruses were distinct from bacteria but could still cause diseases.
• Martinus Beijerinck subsequently coined the term "virus."

Viruses in the 20th Century

• Frederick Twort discovered that bacteria could be infected by viruses.
• Felix d'Herelle demonstrated the ability of viruses to kill bacteria in cell cultures.
• Wendell Stanley crystallized the tobacco mosaic virus, revealing it was mostly protein.
• Viruses were separated into protein and nucleic acid parts.
• Electron microscopy provided the first visualization of viruses.
• John Enders, Thomas Weller, and Frederick Robbins developed human tissue culture techniques to study viruses, which helped produce the first polio vaccine.

Viruses: Filterable Agents (Animal, Human, and Plant)

• Yellow fever vaccine developed in mice - the 17D strain continues to be highly effective.

Techniques in Virology

• Cell culture
• Ultracentrifugation
• Electron microscopy
• Immunological techniques
• Radioisotopes
• Gel electrophoresis
• Recombinant DNA techniques

Definition of Viruses

• Viruses are submicroscopic particles that infect cells.
• Viruses replicate only within a host cell; they cannot reproduce independently.
• Viruses consist of genetic material (DNA or RNA) enclosed by a protective protein coat (capsid).
• Bacteriophages are viruses that infect bacteria.

Origin of Viruses

• Hypothesized origins of viruses include: regressive (degenerative), discard (escape), and coevolution theories.

Importance of Virology

• Understanding dangerous viruses is crucial.
• Some viruses are useful; for instance, in vaccine production.

Atypical Virus-like Agents

• Virions
• Viroids
• Satellites (Satellite Viruses, Virusoids)
• Prions
• Pseudovirions

Satellites and Viroids

• Satellites	Viroids
  Helper virus	-
  Proteins encoded	+
  Genome Replication	Enzymes of helper virus
  Replication Site	As helper (C or N)
  Type of NA and its length	ss circular DNA molecule, 500-2000 nucleotides

Prions and Viruses

• Prion	Virus
  NA	-
  Contain Protein	+ encoded by cellular gene
  UV and Heat effect	+
  Under E.M.	Rod/Filamentous
  Ab Production	-
  Inflammation Production	-

Are Viruses Alive?

• Most virologists consider viruses non-living, similar to obligatory intracellular parasites.
• Viruses are characterized as both living and non-living.
• Viruses are not composed of cells.