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Introduction to Virology
Dr Thanda Kyaw
Department of Virology
UL(Medunsa)/NHLS
Objectives
• At the end of the lecture the learner will be able to
– Draw, label and describe the structure & morphology of viruses
– Describe the important characteristics of viruses
– Understand the different classifications of viruses
– Understand the nomenclature of viruses
– List the steps for viral replication of enveloped and non-enveloped viruses
Virus (Latin, poison)
Viruses are very small <300nm
They can infect all living cells Plants, animals, bacteria
Viruses cannot grow outside the living cell (intracellular parasite)
Viruses do not grow like bacteria, they assemble proteins and genome before being released
They can adapt the environment and change very rapidly
Virus (Virion)
• Acellular particle
• Innermost part is a genome which can be RNA or DNA
• Genome is protected by protein capsid which is made up of small identical protein sub-units called capsomers
• Some viruses has lipid bilayer envelope
• Outermost projections from capsid or envelope is called peplomers
Hellical Nucleocapsid
• Nucleocapsid
• Nucleic acid (genome, RNA or DNA) plus capsid
Virus Classification
• Based on – Nucleic acid (DNA or RNA)- RNA viruses, DNA
viruses
– Morphology: Icosahedral virus, helical virus, enveloped & non-enveloped etc
– Replication strategy (Baltimore classification):group 1-7
– Host species: animal viruses, human viruses etc
– Diseases caused: hepatitis viruses, haemorrhagic fever viruses etc.
Taxonomy of Viruses
• Naming and placement of viral species into the framework
– Order (-virales)
– Family (-viridae)
– Subfamily (-virinae)
– Genus (-virus)
– Species (-virus)
Stages of Viral Replication
• Adsorption
• Entry
• Uncoating
• Transcription (genome is transcribed)
• Synthesis of viral components
• Assembly
• Release
HIV virions are released from the
cell wall by budding
Virus Taxonomy- Example
• Family Herpesviridae
• Subfamily Alfaherpesvirinae
• Genus Simplexvirus
• Species Human herpesvirus 1