Study of Virus

Study of Virus


• Structure of virus

• Classification of virus

• Morphological types of virus

• Cultivation of virus

– Laboratory animals

– Embryonated eggs

– Tissue culture

Intended Learning objectives

At the end of this lecture, the student will be able to:

• Explain the virus structure

• Draw and explain the different morphological types of virus

• Classify virus

• Explain the methods for viral cultivation

Discovery of virus

• The concept of a virus as a distinct entity dates back only to the very late 1800s

• In 1886, the Dutch chemist Adolf Mayer showed that tobacco mosaic disease (TMD) was transmissible from a diseased plant to a healthy plant.

• Ivanoski reported in 1892 that extracts from infected leaves were still infectious after filtration through a  Chamberland filter-candle.

• A new world of filterable pathogens wa

• Beijerinck, in 1898, was the first to call 'virus', the causative agent of the tobacco mosaic.

• He showed that the virus was able to migrate in an agar gel, therefore being an infectious soluble agent

He described the agent of mosaic disease of tobacco as a “contagium vivum fluidum”, or contagious living fluid, because he was convinced the infectious agent had a liquid nature.

• The first human disease associated with a filterable agent was yellow fever.

• By the 1930s, scientists had begun using the word virus, the Latin word for poison, to describe these filterable agents.

• Advances in the molecular biological techniques in the 1980s and 1990s led to the recognition of several new viruses including

– Human Immunodeficiency Virus (HIV)

– SARS associated coronavirus.

• Wendell M. Stanley crystallized and described the molecular structure of the tobacco mosaic virus (TMV) in 1935, showing that it has properties of both living and non-living matter.

• At about the same time, the invention of the electron microscope made it possible to see viruses


• Virus – obligate intracellular parasite

• They do not belong to prokaryotic or eukaryotic cell type

• Basically made up of nucleic acid (DNA or RNA) covered by capsid

• Envelope may or may not be present

• Morphologically virus are classified as helical, polyhedral and complex virus

• Virus can be cultivated in lab animals, embryonated eggs or in tissue culture

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