Introduction to viruses

Introduction Introduction to to viruses viruses Lecture topics - 1 Lecture topics - 1 • What is a virus?  Definition  Structure and replication • Human virus infections • Treatment  Antivirals  Vaccines Lecture topics – 2 Lecture topics – 2 • Immunity to viruses  Cell-mediated  Humoral • Role of Complement • Vaccination against viruses  Inactivated vaccines  Live vaccines • Interferon Definition of a Virus 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 Definition of a Virus Obligate Intracellular Parasite Virion Structure Virion Structure Nucleic Acid Spike Projections Protein Capsid Lipid Envelope Virion Associated Polymerase Virion Morphology Virion Morphology • Simple Structure • Repetitive Structure • High Level of Redundancy Virus Morphology Virus Morphology Helical Icosahedral Virus Replication Virus Replication 1 Virus attachment and entry 1 1 2 Uncoating of virion 2 2 3 Migration of genome nucleic acid to nucleus 3 3 4 Transcription 5 Genome replication 4 4 5 5 6 Translation of virus mRNAs 6 6 7 Virion assembly 7 7 8 Release of new virus particles 8 8 Cytopathic Effect (cpe) Cytopathic Effect (cpe) Adenovirus Herpes virus [...]... extensive antigenic variation Major cause of respiratory infections 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 Weekly consultation rates for influenza...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 Virus Tissue Tropism • Targeting of the virus to specific tissue and cell types • Receptor Recognition  CD4+ cells infected by HIV  CD155 acts as the receptor for poliovirus... cells infected by HIV  CD155 acts as the receptor for poliovirus In vivo Disease Processes • Cell destruction • Virus-induced changes to gene expression • Immunopathogenic disease Acute Virus Infection Amount of virus Symptoms Virus Time Acute Virus Infections • Localised to specific site of body • Development of viraemia with widespread infection of tissues Poliovirus Poliovirus Properties of the virus... of the Royal College of General Practitioners, 1988 to 1999 Rate per 100 000 population 600 500 Epidemic activity 400 300 200 Higher than expected seasonal activity Baseline activity Normal seasonal activity 100 0 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 Year CDR Weekly Report: 5th November 1999 Generation of Novel Influenza A Viruses Human H2N2 ANTIGENIC SHIFT Genetic Reassortment... Year CDR Weekly Report: 5th November 1999 Generation of Novel Influenza A Viruses Human H2N2 ANTIGENIC SHIFT Genetic Reassortment Avian H3N8 Point mutation of HA and NA genes ANTIGENIC DRIFT Human H3N2 Viruses and Human Tumours • Epstein Barr Virus  Burkitt’s Lymphoma • Human papillomavirus  Benign warts  Cervical Carcinoma • Human T-cell Leukaemia Virus (HTLV-1)  Leukaemia • Hepatitis C virus ... Cell ? Uncontrolled cell growth and tumour formation Virus-induced transformation Normal cells Transformed cells 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 Treatment and Prevention of Virus Infections • Antivirals • Vaccines and immunisation