Introduction to medical virology

1. virus
Acellular infectious agent
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A nucleic acid surrounded by a protein coat
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Obligate parasite-they need to reproduce in host
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Does not carry out metabolism
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Lacks organelles and ribosomes.
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20 - 300 nm in size
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structure of virus
protein coat (capsid)
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have genetic material of single stranded DNA or ds RNA
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components of the virus (Genome )
Positive sense RNA (Coding Strand) : RNA that can be used for a template used for protein synthesis
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Negative sense RNA (Template Strand): Complementary to mRNA and cannot be used in protein
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synthesis
Viral structure;
1) Helical; nucleic acid surrounded by a hollow protein cylinder or capsid.
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2) icosahedral: nucleic acid surrounded by a polyhedral (many-sided) shell or capsid, usually in the
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form of an icosahedron (shaped of capsid that contains 20 faces)
3) Envelope;
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plasma membrane covering the protein coat.
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functions to protect the nucleic acid from physical damage, chemical damage and enzymatic damage
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Enveloped viruses are usually released from the host cell by exocytosis.
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Naked viruses are usually released from the host cell by host cell lysis.
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4) binal (complex) viruses; have neither helical nor polyhedral forms, are pleomorphic (irregular
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shaped), or have complex structures.
Viral replication;
1.Attachment:spikes bind to cell receptors by viral attachment proteins = receptor-ligand mediated
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2.Pentrating: virus goes from outside to inside (Viral DNA injected into host cell)
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3.Uncoating: viral nucleic materials open
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4.Sythesis: RNA used to make more RNA and make new molecule, capsomere and spikes then replicate
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a) Early Phase: mRNA and Protein Synthesis;
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Proteins to shut off host cell
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Proteins to replicate viral genome
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b) Eclipsed Phase; Replication of the genome
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c) Late Phase; mRNA and Protein Synthesis ( Structural proteins)
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5. Assembly: make nucleocapsid from RNA and capsomere
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6.Release: enveloped bud off and naked lyse the cell
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Spread
Viruses are spread basically by the same mechanism as other pathogens.
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3 Formal Taxonomic groups;
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1) Togavirus encephalitis viruses
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2) Flavivirus
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3) Bunyavirus
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3. DNA Viruses
DNA viruses are double stranded (except parvovirus).
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DNA viruses are icosahedral (Except poxvirus) and replicate their DNA in the nucleus (except poxvirus)
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1) Double-stranded DNA viruses;
Poxviridviruses
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Herpesviridviruses
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Papillomaviridviruses
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Polyomaviridviruses
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Adenoviridviruses
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2) Single-stranded DNA viruses;
Paroviridviruses
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3) Naked viruses;
Parvovirus
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Papillomavirus
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Adenovirus
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4) Enveloped;
Herpesviridviruses
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Poxvirus
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Hepadnovirus
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5) only DNA virus that replicates its DNA through an RNA intermediate;
Hepatitis B (Hepadnovirus)
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4. 6) only DNA virus that DOES NOT replicate its DNA in the nucleus and NOT
icosahedral;
Poxvirus ( only cytoplasm)
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7) Parvovirus B19 infection;
Erythema infectiosum (Fifth disease) in children, Anemia
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DNA virus Life cycle of herpes; (Syncytia Formation)
Attachment and penetration by fusion;
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Early; protein synthesis
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Active replication; Protein synthesis and genome replication
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Late; protein synthesis ( structural proteins)
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Positive sense:
viral genome directly tlned into protein.
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5. Negative sense:
viral genome must be transcribed into mRNA via viral-encoded transcriptase before tln
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