DISCOVERY OF VIRUSES: AN EPIC TALE
You may have noticed that in the past two years, we have been jailed! We are sequestered in our homes, quite literally, by a small microscopic virus called COVID-19. The power of this little microscopic being is such that it can make us sick, and even cause fatality. But how did the term "virus" come into being and how far does our knowledge of it go back?
To understand what exactly a virus is, we need to understand the history of its discovery. How difficult it must have been for scientists in the 1800s to figure out a microorganism that is non-living outside the host but awakens, or comes alive, when it infects a host. How does it hijack the host reproduction facility and turn it into a virus-making factory?
It’s all very interesting, isn’t it?
Human beings didn’t know of the existence of viruses until the late 1880s. Scientists went to great lengths to understand viruses, infecting animals with viruses to learn about their mode of action.
Jacob Henle in the 1840s hypothesised that there may be infectious agents that were too small to be identified under a light microscope. However, at that time, there was no other method discovered to find those small organisms. some decades later, Dimitry Ivanofsky (1864–1921) on February 12, 1892, said his research could not satisfy Koch’s postulates and could not isolate the "causative agent" of Tobacco mosaic disease.
Martinus Beijerinck, also known as the father of virology, made a conceptual leap about an agent that could reproduce and also pass through a chamberland filter. He called it "Contagium vivum fluidum," or "a contagious living liquid."
Mayer, Ivanofsky, and Beijerinck contributed to the development of the concept of the virus. Sometimes later, the term "virus became restricted to the common parlance. The pioneering work of the TMV, Loeffler and Frosch was able to isolate and identify the agent that caused the foot-and-mouth disease.
Frederick W. Twort, in 1915, tried to culture viruses and saw plaque formation, that is, a small clearing in a lawn of bacterial culture. He hypothesised that the viruses were able to kill a colony of bacteria by producing a clear zone or a plaque. He termed these viruses "bacteriophages."
Other notable scientist working on this was Felix d’Herelle. His research on Shigella dysentery infection of French soldiers in August of 1915 showed a clear circular growth from filtered faecal emulsions. He termed them Taches vierges, or plaques. This kind of experiment also gave rise to virus titer by plaque assay tests. dHerelle’s study also brought about the concept of lysogeny and gave a brief glimpse of the host hijacking theory.
In 1936, Max Schlesinger was able to purify phages and show that they had DNA and proteins in equal proportions.
Max Delbruck, a physicist at the University of Gottingen, developed a quantum mechanical model of the gene in 1937 and started working on bacteriophages, discovering T2, T4, T6 and their replication machinery, and analysed the relation between the genetic information and how it determined the structure and function of the viruses. Delbruck, along with Emory Ellis, showed the step involved in viral replication. The one-step growth curve was formulated.
Tom Anderson, an electron microscopist, along with Delbruck, collaborated to bring forth the first clear pictures of bacteriophages.
The first human viruses were discovered by Walter Reed and his colleagues. They discovered the yellow fever virus in 1901 in Cuba.
Modern concepts of virology came about from the 1950s to the 1975s. These ideas and discoveries are still used today.Seymour Cohen and Wendell Stanley are the most noted scientists in this field of modern virology, who worked hard to research virus infection on RNA and DNA levels in infected cells. They used colorimetric analysis and also found a cessation of RNA accumulation in infected hosts, the first demonstration of mRNA and how host DNA synthesis halts for 7 minutes after infection and then resumes at a 5-to-10-fold increased rate.
Monod and Wollman researched how viral infection stops the inducible β galactosidase enzyme from being produced.
The famous Hershey and Chase experiment was performed in 1952 with the help of viruses to determine whether DNA or Protein passes on genetic information! And that’s how we know it's DNA that passes on our genetic information to the next generation.
More research is being done to gather knowledge about these intriguing microorganisms that cohabit with us. In the coming years, we can expect to see many new discoveries about viruses, as well as vaccines developed and tested by pharmaceutical companies and scientists.