virol 2015
DESCRIPTION
mmmTRANSCRIPT
EMERGING VIRAL DISEASES• HIV/AIDS• Hantavirus pulmonary syndrome (HPS)• West Nile encephalitis (WNV)• Severe acute respiratory syndrome (SARS)• Monkey pox• Human metapneumovirus• 2009 H1N1 pandemic influenza• Ebola• MERS-CoV
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Consequences of viral infections
• 50% of all absenteeism• Children: 7 or more viral infections per year that
involve a visit to a physician• Suffering, followed by recovery• Persistent disease• Fatal disease• Congenital disease• Contributory factor in cancer• Contributory factor in other diseases
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SOME ARE ASYMPTOMATIC!
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VIRUSES CAN BE USEFUL
• VACCINE DEVELOPMENT
• GENE THERAPY
• TOOLS TO INVESTIGATE HOST CELLS
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BASIC STEPS IN VIRAL LIFE CYCLE
• ADSORPTION• PENETRATION• UNCOATING AND ECLIPSE• SYNTHESIS OF VIRAL NUCLEIC ACID AND PROTEIN• ASSEMBLY (maturation)• RELEASE
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What are viruses?
• Small obligate intracellular parasites• Virion
– Complete virus particle : nucleic acid + protein coat, which may be surrounded by an envelope
• Viral Genome– EITHER RNA or DNA genome surrounded by a protective
virus-coded protein coat (Capsid)• Propagation depends on specialized host cells supplying the
machinery for replication, metabolism and biosynthesis
• The DNA or RNA genome may be :– ss – single stranded or– ds – double stranded
• Genomes may be either:– (+) sense: Positive-sense viral RNA is identical to
viral mRNA and thus can be immediately translated into protein by the host cell.
OR– (-) sense: Negative-sense viral RNA is
complementary to mRNA and thus must be converted to positive-sense RNA by an RNA polymerase before translation.
• Retroviruses?
Definitions
• Bacteriophage– Virus that infects prokaryotic (bacterial) cells.
• Nucleocapsid: – viral nucleic acid + the protein coat that encloses
it.– Represents the packaged form of the viral
genome.
Viral Structure - Overview
Fig 1. Schematic overview of the structure of animal viruses
** does not exist in all viruses
Nucleic acid
CapsidNucleocapsid
Envelope protein
Membrane proteinViral envelope**
Spike protein
Virus & Bacteriophage
http://micro.magnet.fsu.edu/cells/virus.html
Viral Structure
Figure 1 An array of viruses. (a) The helical virus of rabies. (b) The segmented helical virus of influenza. (c) A bacteriophage with an icosahedral head and helical tail. (d) An enveloped icosahedral herpes simplex virus. (e) The unenveloped polio virus. (f) The icosahedral HIV with spikes on its envelope.
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HERPESVIRIDAEHEPADNAVIRIDAE
ENVELOPED
PAPILLOMAVIRIDAEPOLYOMAVIRIDAE(formerly grouped together as the PAPOVAVIRIDAE)
CIRCULAR
ADENOVIRIDAE
LINEAR
NON-ENVELOPED
DOUBLE STRANDED
PARVOVIRIDAE
SINGLE STRANDEDNON-ENVELOPED
POXVIRIDAE
COMPLEXENVELOPED
DNA VIRUSES
Modified from Volk et al., Essentials of Medical Microbiology, 4th Ed. 1991
All families shown are icosahedral except for poxviruses
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FLAVIVIRIDAETOGAVIRIDAE
RETROVIRIDAE
ICOSAHEDRAL
CORONAVIRIDAE
HELICAL
ENVELOPED
ICOSAHEDRAL
PICORNAVIRIDAECALICIVIRIDAEASTROVIRIDAE
NONENVELOPED
SINGLE STRANDEDpositive sense
BUNYAVIRIDAEARENAVIRIDAE
ORTHOMYXOVIRIDAEPARAMYXOVIRIDAE
RHABDOVIRIDAEFILOVIRIDAE
SINGLE STRANDEDnegative sense
REOVIRIDAE
DOUBLE STRANDED
RNA VIRUSES
ENVELOPED
HELICAL ICOSAHEDRAL
NONENVELOPED
Modified from Volk et al., Essentials of Medical Microbiology, 4th Ed. 1991
