Viruses

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Viruses
Sunita Kaushik Department of Botany DAVCG,
Yamunanagar
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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.
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Definition of a Virus
Obligate Intracellular Parasite
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Virion Structure
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Virion Morphology

• Simple Structure
• Repetitive Structure
• High Level of Redundancy

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Virus Morphology
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Virus Replication
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Cytopathic Effect (cpe)
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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

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In vivo Disease Processes

• Cell destruction
• Virus-induced changes to gene expression
• Immunopathogenic disease

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Acute Virus Infection
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Acute Virus Infections

• Localised to specific site of body
• Development of viraemia with widespread infection
  of tissues

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Poliovirus
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Poliovirus
Properties of the virus

• Enterovirus.
• Possesses a RNA genome.
• Transmitted by the faecal oral route.
• Cause of gastrointestinal illness and
  poliomyelitis.

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Poliovirus Infection
Non-neuronal tissues
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Incidence of Poliomyelitis
Poliovirus vaccines A Salk killed inactivated
vaccine. B Sabin live attenuated
vaccine
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Influenza A virus
Properties of the 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

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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

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Spread of influenza virus
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Respiratory Tract
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Generation of Novel Influenza A Viruses
ANTIGENIC SHIFT
ANTIGENIC DRIFT
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Viruses and Human Tumours

• Epstein Barr Virus
• Burkitts Lymphoma
• Human papillomavirus
• Benign warts
• Cervical Carcinoma
• Human T-cell Leukaemia Virus (HTLV-1)
• Leukaemia
• Hepatitis C virus
• Liver carcinoma

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Virus-induced tumours
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Virus-induced transformation
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Virus-Induced Tumours

• Virus infects cell.
• Virus nucleic acid, as DNA, integrates into
  cellular genome.
• Virus causes changes in cellular gene expression.
• Uncontrolled cell multiplication and tumour
  formation.

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Treatment and Prevention of Virus Infections

• Antivirals
• Vaccines and immunisation

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Antiviral Targets

• Attachment/Entry
• Nucleic acid replication
• Virus protein processing
• Virus maturation

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Problems with Antivirals

• Identification of virus-specific target.
• Generation of resistant variants.