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
Lipid Envelope Nucleic Acid Protein Capsid Virion Associated Polymerase Spike Projections Virion Structure
Virion Morphology • Simple Structure • Repetitive Structure • High Level of Redundancy
Helical Icosahedral Virus Morphology
1 Virus attachment and entry 1 2 Uncoating of virion 3 Migration of genome nucleic 5 acid to nucleus 4 Transcription 4 2 5 Genome replication 6 Translation of virus 3 mRNAs 7 Virion assembly 7 8 Release of new virus particles 6 8 Virus Replication
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 Properties of the virus • Enterovirus. • Possesses a RNA genome. • Transmitted by the faecal oral route. • Cause of gastrointestinal illness and poliomyelitis.
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
Other Viral Infections • Herpes • Hepatitis • Rhinovirus • HIV • Ebola • Measles • Mumps • Smallpox • Chickenpox
Human H2N2 Human H3N2 Genetic Reassortment Avian H3N8 Point mutation of HA and NA genes Generation of Novel Influenza A Viruses ANTIGENIC SHIFT ANTIGENIC DRIFT
Antiviral Targets • Attachment/Entry • Nucleic acid replication • Virus protein processing • Virus maturation
Problems with Antivirals • Identification of virus-specific target. • Generation of resistant variants.