Study of Virus
Contents
• 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
Summary
• 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
