Medical Virology Course Lecture Notes PDF

MEDICAL VIROLOGY COURSE The course is composed of 20-26 lectures The 1st 5 lectures deal with basic virology. The rest of the lectures deal with medical virology. Ref. 1- Jawiet’s Medical Microbiology 2010 2-Medical Microbiology & Immunology (Exam- inatio...

MEDICAL VIROLOGY COURSE The course is composed of 20-26 lectures The 1st 5 lectures deal with basic virology. The rest of the lectures deal with medical virology. Ref. 1- Jawiet’s Medical Microbiology 2010 2-Medical Microbiology & Immunology (Exam- ination and board review) 2010. 3- Clinical and diagnostic virology 2009. 4- Human and medical virology 2010,  MEDICAL VIROLOGY LECTURE 1 General properties and Classification of Viruses  Term virus (Latin for poisonous liquid) The existence of viruses was first suspected in the nineteenth century when it was shown that filtered extract of infective material passed through filters (filterable material) ‫))الرواشح‬  Order of viruses Order (-virales) Family (-viridae) Subfamily (-virinae) Genus (-virus) Species Species names generally take the form of [Disease] virus  VIRUSES Viruses are the smallest infectious agents (20-300 nm in diameter), and contain only one kind of nucleic acid (DNA or RNA) encased in a protein shell which may be surrounded by a lipid containing membrane. They are obligate intracellular parasites.  Are Viruses living or nonlivinig?? There is an ongoing debate as to whether viruses are living or nonliving; the view taken depends on how life is defined. Viruses are therefore parasites of cells, and are dependent on their hosts for most of their requirements, including 1. building-blocks such as amino acids and nucleosides; 2. protein-synthesizing machinery (ribosomes); 3. energy, in the form of adenosine triphosphate  Definitions in virology Capsid: The protein shell (or coat) that surrounds the nucleic acid genome. Capsomeres: The morphological units that form the capsid and represent clusters of polypeptides.  Definitions in virology Nucleocapsid: The protein- nucleic acid complex representing the packaged form of the viral genome. Virion: The complete virus particle. In some instances (e.g. picornaviruses) it is identical to the nucleocapsid. In more complex viruses (e.g. herpesviruses) it includes the nucleocapsid plus the envelope.  Definitions in virology Envelope: A lipoprotein membrane that surrounds some virus particles, it is acquired during viral maturation by budding through the cellular membrane. There are frequently glycoprotein spikes on the surface, that play role in attachment of virus to host cell.  Viral Structure - Overview Nucleic acid Nucleocapsid Capsid Envelope protein Viral envelope** Membrane protein Spike protein Schematic overview of the structure of animal viruses ** does not exist in all viruses  Viral Symmetry 1-Icosahedral (cubic symmetry): the capsomeres arranged in 20 triangles that form a symmetric figure. 2-Helical: the capsomeres arranged in a hallow coil that appears rod-shaped. 3-Complex: Neither cubic nor helical but more complex. Icosahedral symmetry Helical symmetry  Viral Symmetry (a) The helical virus of rabies. (b) The segmented helical virus of influenza. (c) A bacteriophage with an icosahedral head and helical tail. (d) An enveloped icosahedral herpes simplex virus. (e) The unenveloped polio virus. (f) The icosahedral HIV with spikes on its envelope.  Viruses have either an RNA or DNA genome (never both) and are classified in families on the basis of their genome (RNA or DNA) and whether it is single or double stranded (SS or DS). Furthermore, Single-stranded RNA viruses are either a negative (_RNA) or a positive (RNA) strand as this affects their replication strategy. As a rule of thumb all DNA viruses, except those belonging to Parvoviridae and Circoviridae are double stranded, and all RNA viruses except those belonging to Reoviridae and Birnaviridae are single stranded  Differences DNA (D) vs RNA (R ) viruses DNA viruses RNA viruses 1 Almost always double stranded Almost always single stranded 2 Replicate in nucleus Replicate in cytoplasm 3 Usually rely on host DNA polymerase for Can not use host polymerases, use special RNA- replication and host RNA polymerase for dependent RNA polymerase for replication and transcription transcription 4 No such classification -ve sense ss RNA virus: the genome is template for mRNA +ve sense ssRNA virus: the genome is itself mRNA 5 Usually do not bring its polymerase -ve sense RNA virus: has to bring its polymerase enzymes with it as it rely on host enzymes enzyme with it to initiate the transcription first entirely or at least at the beginning then it kick transcribe its own +ve sense RNA virus: optional, might not bring its polymerase as the genome acts as mRNA immediately translated 6 Some viruses can integrate into the Can not unless RNA genome is reverse chromosome of the host oncogenic transcribed from RNA to DNA such as in retroviruses (eg. HIV) 7 More oncogenic less oncogenic (exception only the retroviruses)  Classification of viruses The two major components of the virus used in the classification are: 1-The type of the nucleic acid (DNA or RNA). 2-The capsid (its symmetry, size, and whether it is enveloped or not).  Classification of viruses Other viral components used in classification: 3. Molecular mass, pH stability, thermal stability, susceptibility to chemicals (e.g. ether)…etc/ 4. Antigenic properties. 5. Biologic properties, including natural host range, mode of transmission, vector relationships, pathogenicity, tissue tropisms, and pathology Baltimore classification of viruses  DNA Viruses Envelope Medically important Virus Family Capsid symmetry presence viruses Parvovirus No icosahedral B19 virus Papovavirus No icosahedral Papillomavirus Adenovirus No icosahedral Adenovirus Hepadnavirus Yes icosahedral Hepatitis B virus Herpesvirus Yes icosahedral HSV, VZV, CMV, EBV Poxvirus Yes complex Smallpox, vaccinia viruses  RNA Viruses Envelope Capsid Virus Familly Medically important viruses presence symmetry Picornavirus No Icosahedral Polio, rhino, hepatitis A virus Calicivirus No Icosahedral Norwalk, hepatitis E virus Reovirus No Icosahedral Reo, rota virus Flavivirus Yes Icosahedral Yellow fever, hepatitisC virus Togavirus Yes Icosahedral Rubella virus Retrovirus Yes Icosahedral HIV, HTLV Orthomyxovirus Yes Helical Influenza virus Paramyxovirus Yes Helical Measles, Mumps, RSV Rhabdovirus Yes Helical Rabies virus Filovirus Yes Helical Ebola virus Coronavirus Yes Helical Coronavirus Arenavirus Yes Helical Lymphocytic choriomeningitis virus Bunyavirus Yes Helical California encephalitis virus Deltavirus Yes Uncertain Hepatitis D virus RNA Viruses