Viruses PDF

VIRUSES By: Dr. Nagat Balaman (MD, PhD). Aesthetic doctor Medical & Clinical Microbiologist GAU Faculty of Pharmacy  Smallest infectious agents (18-600 nm). Filterable agents. Can not be seen by ordinary microscope.  Can not synthesize their own proteins thus they can not form t...

VIRUSES By: Dr. Nagat Balaman (MD, PhD). Aesthetic doctor Medical & Clinical Microbiologist GAU Faculty of Pharmacy  Smallest infectious agents (18-600 nm). Filterable agents. Can not be seen by ordinary microscope.  Can not synthesize their own proteins thus they can not form their own energy. Obligate intracellular parasite -----Need a host Non-living infectious agents. Viral genome can be RNA or DNA (But not both). Virus Cell nucleus  Virus Taxonomy According to ICTV, the classification is as follows: Order – virales (suffix) Family – viridae Subfamily – virinae Genus – virus Species –(trivial name preserved) (ICTV) International Committee on Taxonomy of Viruses. Nomenclature of Viruses:  Structure of viruses: ▪ The complete, infective form of a virus outside a host cell is called a Virion: Nucleic acid genome (single- or double- stranded RNA or DNA). Protein coat (Capsid): which is made up of capsomeres. The nucleic acid genome Enveloped virus Naked plus the protective protein virus coat is called the nucleocapsid. Structure of viruses: Envelope: viruses obtain Enveloped virus their envelope by budding through a host cell membrane/ internal cell membranes such as those of the Golgi body or the nucleus. *Compose of lipids, protein and glycoprotein (may/ may not has). Viral attachment protein (VAP): They are surface structures of the envelop Naked virus and the capsid. Classification: A. Viral structure. Naked enveloped B. Genome Structure. DNA or RNA, Single-stranded or double-stranded Segmented / nonsegmented. C. Capsid Symmetry. A. Viral structure Naked Enveloped  Naked Viruses Ressistant to the environmental conditions – Heat, acid, proteases, detergants , dryness Easily transmitted – (object and surfaces, hand-to-hand transmission) Many can be transmitted via fecal-oral route Nacked virus Enveloped viruses They cannot withstand conditions that naked viruses are resistant to. Enveloped viruses are comparatively fragile. Most are labile to treatment with acid and detergents, a feature that precludes their being transmitted by the fecal-oral route. They must remain wet and spread – In respiratory droplets, blood, mucus, saliva and semen, – By injection, or – Organ transplants Retroviridae B. Genome structure. DNA or RNA, Single-stranded or double-stranded Segmented / non-segmented. RNA viruses Medically important viruses: DNA viruses o Parvovirus o Polyomavirus o Papillomavirus o Adenovirus o Herpesvirus o Hepadnavirus o Poxvirus Medically important viruses: ▪ RNA viruses o Picornavirus o Astrovirus o Calicivirus ▪ RNA viruses o Reovirus o Arenavirus o Togavirus o Coronavirus o Flavivirus o Retrovirus o Bunyavirus o Orthomyxovirus o Paramyxovirus o Rhabdovirus o Filovirus  DNA viruses Enter the nucleus and gets integrated into the genome Uses host cell machinery for protein synthesis and replication Larger, more complex viruses (Parvoviruses, Hepadna virus) encode their own polymerases. Viral polymerases are usually faster but less precise than host cell polymerases. Poxviruses have their enzymes in their nucleocapsid as they replicate in cytoplasm  (+) sense RNA viral genome The viral (+)sense RNA can directly act as cellular mRNA. Can bind to ribosomes Can be used directly in protein synthesis. Sufficient to start infection itself i.e. infectious. After the virus-encoded , RNA-dependent RNA polymerase is produced, a negative strand RNA template is synthesized. The template can then be used to generate more mRNA and to replicate the genome. (+) sense RNA viral genome Picornaviruses Caliciviruses Coronaviruses Flaviviruses Togaviruses  (-) sense RNA virus They are not sufficient to start infection on their own i.e. non-infectious by itself A polymerase must be carried into the cell with the genome. A full-lenght (+) strand RNA must also be produced by the viral polymerase to act as a template to generate more copies of the genome. Transcription and replciation of (-)stranded RNA viruses occur in cytoplasm. (Except for influenza viruses). (-) sense RNA virus Rhabdovirus Orthomyxovirus Paramyxovirus Filovirus Bunyavirus Segmented viruses: a)- HIV, b)- Influenza Paramyxoviridae Non segmented C. Capsid Symmetry Icosahedral / cubic/ spherical Heical / pleomorphic Complex  Viral Replication Steps Detection of the target cell Attachment Penetration Uncoating Macromolecule synthesis Virus assembly Release Budding (For enveloped viruses)  Viral attachment proteins Rhinovirus ---VP1-VP2-VP3. Adenovirus --- Fiber protein. Rotavirus --- VP7. Rabies --- G protein. Influenza A --- Hemaglutinin. Epstein-Barr virus --- gp350 / gp220. Measles --- HA. HIV --- gp120. Viral tropism is the ability of a given virus to productively infect a particular cell (cellular tropism), tissue (tissue tropism) or host species (host tropism). Major sites of viral disease Respiratory system. Gastrointestinal system. Skin, mouth and genital mucosal sites. (Epithelial sites) Lymphoid tissues. Liver. Central nervous system. Viral Infection Types Asymptomatic Infections – Subclinical – Latent Symptomatic Infections – Acute Herpesviruses – Subacute – Chronic – Persistent  Viral diseases Viral infections: - The intensity of the viral infection & the symptoms depends: a) Host related factors. b) Viral factors. German Measles (Rubeola)