General virology.pdf

Level 1, Semester 2  Instructor Information Instructor Information Contact Official email Mobile Prof. Niveen Adel Mohamed El- [email protected] 01280064464 wakeel Dr. M...

Level 1, Semester 2  Instructor Information Instructor Information Contact Official email Mobile Prof. Niveen Adel Mohamed El- [email protected] 01280064464 wakeel Dr. Mona Abd Elhamid Abd [email protected] 01007277575 Elraouf Abd Elhamid Dr.Amany Elmatbouly Elsayed [email protected] 01097247264 Dr.Aya Ahmad Elnegery [email protected] 01060345452 Dr. Ayah Mahmoud Fathy [email protected] 01159551168 Dr. Nada Hamid Qandeel [email protected] 01019584306  Explain general characters of viruses, discuss viral structure and list function for each viral structure. Predict the replication cycle of a virus based on the genes it carries. Learning Outcomes Explain the effects of viral infection on host cells. Compare and contrast the different methods used in the laboratory diagnosis of viral infections. Outline the classification of viruses.  Agenda 1. General characters of the virus 2. Viral structure and Symmetry 3. Viral classification 4. Viral replication cycle 5. Laboratory diagnosis  Case scenario A previously healthy 9-month-old infant presented with a 2-day history of irritability, fever, and upper respiratory congestion. The mother reported that over the previous 24 hours the child had difficulty breathing with coughing and wheezing. On examination the child was feverish (38.6°C), tachypnic with tachycardia. Examination shows the child to be in moderate respiratory distress. Laboratory diagnosis for bacterial and fungal infections were excluded by negative culture results What is the likely infectious cause of her respiratory illness? What are methods of laboratory diagnosis of the case ? General characters of viruses  They are the smallest infectious agents know, range from 20 to 300 nm in diameter. Can be seen only by Electron Microscope.  They infect man, animals, plants and bacteria.  In contrast to bacteria, fungi and parasites, viruses are not cells  They contain one kind of nucleic acid (RNA or DNA).  They do NOT have ribosomes, so they are obligate intracellular parasites, hence they can not grow in artificial medium  Structure and assembly of viruses  Structure of viruses: Each virus particle or “virion” is composed of – Protein coat (capsid). – Nucleic acid core. – Envelope: many viruses are naked, some are enveloped. Capsid + Nucleic acid= Nucleocapsid Many viruses are naked but some viruses are enveloped 1- Viral capsid: - Surrounds viral nucleic acid - Made up of subunits called capsomers - Each capsomer consists of one or several proteins -The capsid with the enclosed nucleic acid is called nucleocapsid Functions of the capsid: 1) Protects the viral genome against inactivation by nuclease enzymes. 2) Gives shape ‘symmetry’ of the virus (icosahedral, helical or complex) 3) Role in viral replication “attachment step” 4) Determines the antigenicity of the virus. Viral Symmetry: 1- Icosahedral (enveloped and non enveloped) 2- Helical (enveloped) 3- Complex (enveloped)  2-Viral Nucleic Acid (genome): - DNA or RNA - Single or double stranded - linear or circular - Segmented or non segmented - It is the infectious part of the virus (Codes viral structural and non- structural proteins) 3- Viral envelope: in some viruses - Lipoprotein in nature:  Lipid from host cell membrane.  Protein is virus specific - Contains ‘glycoproteins’ which are spike-like projections on the surface of the virus, which attach to the host cell receptors during infection (attachment) -Determines virus specificity & antigenicity  Quiz!!! What is the basic structure of virus? The infectious part of the virus is the capsid (true or false) Virus Replication cycle  Steps of viral replication Recognition and adsorption. Entry (Penetration). Uncoating. Viral gene expression (transcription) and protein synthesis (translation). Viral nucleic acid synthesis (Replication). Assembly. Release.  Viral Replication 1 Recognition and adsorption: – Attachment of the virus to the host cell. – It is receptor specific. 2 Entry (Penetration): – In non enveloped viruses: penetration occurs by crossing the plasma membrane directly or by receptor mediated endocytosis. – In enveloped viruses: penetration occurs by fusion of viral envelop with cell membrane or with membrane of endosome at cell surface.  Viral Replication 3 Uncoating: – Release of viral nucleic acid by cellular enzymes. – This renders viral nucleic acid accessible for transcription and replication. 4 Viral gene expression  transcription= mRNA synthesis  translation = protein synthesis 5 Viral nucleic acid synthesis (Replication): – By using a strand of parental nucleic acid as template for the production of progeny DNA or RNA molecules.  Viral Replication 5 Assembly: Assembly of viral nucleic acid and protein coats to form mature virus particles 6 Release: Virus particles are released from the cell - In enveloped viruses: by budding through the cell membrane - In non enveloped viruses: Rupture of the cell membrane and release of the mature particles  Effects of viral infection on host cells  a. Lytic infection b. Persistent infection Host cell death Host cell survive but altered antigenically. Production of progeny viruses  c. Abortive infection d. Latent infection No production of progeny Viral genome is present inside viruses a host cell without production Due to defect in either the of progeny viruses. virus or host cell (non- Can be reactivated months or permissive). years in the future leading to productive infection e. Transformation and oncogenesis: By some oncoviruses. e.g. Human Papilloma virus and Epstein Barr virus (EBV).  Quiz!!! What are the steps of viral replication? Mention 5 effects of viral infection on host cell Laboratory diagnosis of the viral infection  Direct detection Serological detection Tissue culture of antibodies Viral isolation Embryonated egg Animal inoculation 1- Direct detection: of a. Virus particles: by electron microscope b. Inclusion bodies (sites of viral replication) by inverted Light microscope c. Viral antigens: by ELISA d. Viral nucleic acid: by PCR 2. Virus isolation: Viruses are obligate intracellular parasites and can be cultivated on: A. Tissue culture: Pieces of animal or human tissues are trypsinizied to get separate cells. Cells are grown in media containing amino acids, vitamins, calf serum and antibiotics A monolayer (sheet) of cells is formed on the flat side of the container (flask) within few days.  Viruses are inoculated on the monolayer. Tissue culture flasks and plates  Types of tissue culture: – Primary cell lines from organ fragments e.g. monkey kidney. – semi-continuous cell line (Human diploid cell lines ): fibroblasts derived from human embryo lung. – Continuous cell lines: from tumor cell e.g. HELA cells. B. Embryonated eggs: influenza virus C. Animal inoculation: was used in the past. It is still used for: – Studying viral oncogenesis – Pathogenesis of viral diseases – Immune response to viruses 3. Serologic detection of antiviral antibodies: By ELISA, Radioimmunoassay (RAI), Immunofluorescence (IF) technique.  Virus Classification  Quiz!!! Viruses can grow on agar media (true or false) All DNA viruses are enveloped (true or false)  Case scenario A previously healthy 9-month-old infant presented with a 2-day history of irritability, fever, and upper respiratory congestion. The mother reported that over the previous 24 hours the child had difficulty breathing with coughing and wheezing. On examination the child was feverish (38.6°C), tachypnic with tachycardia. Examination shows the child to be in moderate respiratory distress. Laboratory diagnosis for bacterial and fungal infections were excluded by negative culture results What is the likely infectious cause of her respiratory illness? What are methods of laboratory diagnosis of the case ? General Virology