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Transcript
Viruses Sarita Department of Botany DAVCG, Yamunanagar 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 Lipid Envelope Nucleic Acid Protein Capsid Virion Associated Polymerase Spike Projections Virion Morphology • Simple Structure • Repetitive Structure • High Level of Redundancy Virus Morphology Helical Icosahedral Virus Replication 1 Virus attachment 2 3 1 5 4 5 6 4 2 3 7 8 7 6 8 and entry Uncoating of virion Migration of genome nucleic acid to nucleus Transcription Genome replication Translation of virus mRNAs Virion assembly Release of new virus particles Cytopathic Effect (cpe) Adenovirus Herpes virus 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 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 • • • • Enterovirus. Possesses a RNA genome. Transmitted by the faecal oral route. Cause of gastrointestinal illness and poliomyelitis. Poliovirus Infection Virus Infection Gut Non-neuronal tissues Viraemia Neuronal tissues Virus excretion in the faeces Paralysis Incidence of Poliomyelitis A B Number of cases (in thousands) 40 Poliovirus vaccines A: Salk – killed inactivated vaccine. B: Sabin – live attenuated vaccine 30 20 10 0 1950 1960 1970 1980 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 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 and influenza-like illness: Weekly Returns Service 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 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 Liver carcinoma Virus-induced tumours Virus Infection [ ] Uninfected 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 Antiviral Targets • Attachment/Entry • Nucleic acid replication • Virus protein processing • Virus maturation Problems with Antivirals • Identification of virus-specific target. • Generation of resistant variants. Thank You…..