survey of viruses
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Survey of Viruses
Chapter 24
Definition of a Virus
Sub microscopic entity consisting of a
single nucleic acid surrounded by a
protein coat and capable of replication
only within the living cells of bacteria,
animals or plants.
Definition of a Virus
Obligate
Intracellular
Parasite
Virion Structure
Nucleic Acid
Spike Projections
ProteinCapsid
Lipid Envelope
VirionAssociatedPolymerase
Virion Morphology• Simple Structure
• Repetitive Structure
• High Level of Redundancy
Virus Morphology
Helical Icosahedral
Virus Replication1 Virus attachment
and entry1 2 Uncoating of virion
2
3 Migration ofgenome nucleicacid to nucleus
3
4 Transcription5 Genome replication4
5
6 Translation of virusmRNAs
6
7 Virion assembly78 Release of new
virus particles
8
Transmission of Viruses• Respiratory transmission
– Influenza A virus• Faecal-oral transmission
– Enterovirus• Blood-borne transmission
– Hepatitis B virus• Sexual Transmission
– HIV• Animal or insect vectors
– Rabies virus
In vivo Disease Processes
• Cell destruction
• Virus-induced changes to gene expression
• Immunopathogenic disease
Acute Virus Infections
• Localised to specific site of body
• Development of viraemia with widespread infection of tissues
Poliovirus
Poliovirus
• Enterovirus.• Possesses a RNA
genome.• Transmitted by the faecal
oral route.• Cause of gastrointestinal
illness and poliomyelitis.
Properties of the virus
Influenza A virus
• Myxovirus• Enveloped virus with a
segmented RNA genome• Infects a wide range of
animals other than humans
• Undergoes extensive antigenic variation
• Major cause of respiratory infections
Properties of the virus
Influenza A virus Infection• Spread by respiratory route• Virus infects cells of the respiratory tract• Destruction of respiratory epithelium
– Secondary bacterial infections
• Altered cytokine expression leading to fever
e.g interleukin-1 and interferon
Spread of influenza virus
Respiratory Tract
Other Viral Infections
• Herpes• Hepatitis• Rhinovirus• HIV• Ebola
• Measles • Mumps• Smallpox• Chickenpox
Point mutation of HA and NAgenes
ANTIGENIC DRIFT
ANTIGENIC SHIFT
Genetic Reassortment
Human H3N2
Avian H3N8
Human H2N2
Generation of Novel Influenza A Viruses
Antiviral Targets
• Attachment/Entry
• Nucleic acid replication
• Virus protein processing
• Virus maturation
Problems with Antivirals
• Identification of virus-specific target.
• Generation of resistant variants.
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