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Viruses are simple, acellular entities consisting of one or more molecules of
either DNA or RNA enclosed in a coat of protein
Either single-stranded or double-stranded DNA or RNA - linear, closed circle,
or able to assume either shape.
Reproduce only within living cells
Virion
All viruses have a nucleocapsid composed of a nucleic acid surrounded by a
protein capsid that may be icosahedral, helical, or complex in structure.
Capsids are constructed of protomers that self-assemble through noncovalent
bonds. A membranous envelope often lies outside the nucleocapsid.
Classification - nucleic acid’s characteristics, capsid symmetry, the presence or
absence of an envelope, their host, the diseases caused by animal and plant
viruses
Virology
The Cultivation of Viruses
Myxoma
Mumps
Monkey kidney cell culture
Cytopathic Effect
Virus Purification
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Differential and density gradient centrifuge
Precipitation of viruses
Denaturation of contaminants
Enzymatic digestion of cell constituents
Virus Purification
Enumeration of Viruses
• PFU
• Microscope
• Hemagglutination Assay
The Structure of Viruses
Virion Size - about 10 to 300 or 400 nm in diameter
General Structural Properties
• Nucleocapsid
• Capsid
There are four general morphological types of capsids and virion structure.
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Icosahedral
Helical
Envelope
Complex viruses
Types of Viral Nucleic Acids
Virus
Taxonomy
1971 - The International Committee for Taxonomy of Viruses
3 orders, 56 families, 9 subfamilies, 233 genera, 1,550 virus species
• Nature of the host—animal, plant, bacterial, insect, fungal
• Nucleic acid characteristics—DNA or RNA, single or double
stranded, molecular weight, segmentation and
• number of pieces of nucleic acid (RNA viruses), the sense of the
strand in ssRNA viruses
• Capsid symmetry—icosahedral, helical, binal
• Presence of an envelope and ether sensitivity
• Diameter of the virion or nucleocapsid
• Number of capsomers in icosahedral viruses
• Immunologic properties
• Gene number and genomic map
• Intracellular location of viral replication
• The presence or absence of a DNA intermediate (ssRNA viruses),
and the presence of reverse transcriptase
• Type of virus release
• Disease caused and/or special clinical features, method of
transmission