Introduction to Virology - with Notes PDF

Introduction to VIROLOGY Prepared by: Mark Raymund G. Nava, RMT, MPA, MSMT INTENDED LEARNING OUTCOMES Discuss the characteristics and major differences of viruses Identify the mode of transmission of viruses Classify viruses according to its genome, shape,and presence of protective coat...

Introduction to VIROLOGY Prepared by: Mark Raymund G. Nava, RMT, MPA, MSMT INTENDED LEARNING OUTCOMES Discuss the characteristics and major differences of viruses Identify the mode of transmission of viruses Classify viruses according to its genome, shape,and presence of protective coating Explain the pathogenicity of viruses PRE-TEST TRUE OR FALSE 1. A virion is only infectious if fully assembled. 2. Viruses are more resistant to antiseptic than bacteria. 3. The ICTV Family name of Reoviridae is now Sedoreoviridae. 4. Poxviridae is the only DNA virus family that assembles its virion in the cytoplasm. 5. There are 8 classes under Baltimore classification.  Dependency on Host Cells VIRUSES lack ribosomes, mitochondria, and other components Once inside a host cell replicate their genetic material and produce new virions (virus particles). Intracellular organism Unable to reproduce itself outside a living host cell To reproduce, a virus must: Attach to a susceptible host cell. "obligate intracellular parasites" Enter the cell or inject its genetic material. Use the host's machinery to replicate its genome and produce viral proteins. Assemble new viral particles. Exit the host cell (often damaging or killing it) to infect other cells. Viruses are highly specific  Complete Viral Particle envelope viral proteins that help the virus enter host VIRION Infectious Only When Fully Assembled cells Non-enveloped only have the genome and capsid the entire infectious unit or viral particle complete viral particle it is only infectious if FULLY assembled consist of: core – GENOME DNA or RNA protective coat – CAPSID protein shell that encases and protects the viral geno CAPSOMERES protein subunits recognizing and binding to the host cell during the infection process to protect the viral genome and aid in the infection process  Picornaviruses (e.g., Poliovirus) 20–30 nm in diameter VIRUSES Poxviruses (e.g., Variola virus) 200 nm in diameter SIZE: 20 – 200 nm HIV diploid single copy of their genetic material All viruses HAPLOID except Retrovirus Attachment to a host cell. no mitochondria acellular and do not have organelles viral replication Penetration into the host cell. Replication of viral genome and production of viral proteins using the host's machinery. do not multiply by binary fission Assembly of new virions. Release of newly formed virions to infect other cells. capable only of replicating within the cell  Resistance of Viruses resistant to antimicrobials and antibacterials more resistant to antiseptic than bacteria can survive long periods (freeze dried at -70°C) Viruses are generally more resistant to antiseptics compared to bacteria No cell wall or membrane No protein synthesis machinery Viral Structure: Antiseptic Mechanisms Environmental Resistance  Inactivation of Viruses refers to processes or agents that disrupt the viral structure or function UV and X-ray UV light causes damage to the viral genome, primarily by forming pyrimidine dimers (e.g., thymine dimers) in the DNA or RNA of the virus X-rays cause breaks in the viral DNA or RNA, leading to the loss of viral Chloroform and Ether replication ability Sodium hypochlorite and Formalin (combination) Formalin works by cross-linking proteins and nucleic acids, effectively These solvents dissolve the lipid bilayer of enveloped viruses, causing the "fixing" the viral particles and rendering them inactive virus to lose its outer protective membrane Cause direct damage to viral genetic material (DNA/RNA), preventing replication Sodium hypochlorite acts as an oxidizing agent, breaking down proteins, lipids, and nucleic acids in the virus. Act as powerful chemical disinfectants Target the lipid envelope of viruses, disrupting their outer layer and rendering enveloped viruses non-infectious  Transmission of Viruses DROPLET INFECTION Prevention of Droplet Infection: Example: Influenza virus Physical Barriers: Hygiene Measures: tiny respiratory droplets expelled when an infected person coughs, sneezes, talks, or breathes Vaccination Key Aspects of Droplet Transmission: Droplet Size Inhalation of Droplets Surface Contamination  Transmission of Viruses DIRECT CONTACT Prevention of Direct Contact Transmission Hygiene Practices Example: Papilloma virus Barrier Protection the spread of viruses through physical contact between an infected Vaccination individual and a susceptible person virus is transferred via skin-to-skin contact, bodily fluids, or contact with infected surfaces and lesions Key Aspects of Direct Contact Transmission Physical Contact Contact with Contaminated Surfaces or Objects Entry Points  Transmission of Viruses Prevention of Direct Inoculation Transmission DIRECT INOCULATION Animal Vaccination and Control Example: Rabies virus Immediate Medical Treatment bites, punctures, or injections Needle Safety in Healthcare Key Aspects of Direct Inoculation Transmission Introduction through Skin or Mucous Membranes Bites and Animal Vectors Needle Sticks and Contaminated Instruments  Transmission of Viruses TRANSPLACENTAL Example: Herpes simplex virus transfer of a virus from a pregnant individual to the Congenital Infections fetus through the placenta Prevention Mechanism of Transplacental Transmission Screening and Management Viral Entry Placental Crossing Fetal Infection  Transmission of Viruses Symptoms and Disease: INGESTION Hepatitis A primarily causes liver inflammation, leading to symptoms such as: Fatigue Example: Hepatitis A virus Nausea Abdominal pain Jaundice (yellowing of the skin and eyes) entry of viruses into the body through the oral route, usually through contaminated food or water Prevention Mechanism of Transmission via Ingestion Vaccination Source of Contamination Hygiene Practices Ingestion Food Safety Viral Replication Shedding  Transmission of Viruses INSECT-BORNE/ ARTHROPOD-BORNE Example: Dengue Virus Prevention the bites of infected insects or arthropods, such as Vector Control mosquitoes, ticks, and fleas Eliminating standing water where mosquitoes breed Using insect repellent on exposed skin. Installing screens on windows and doors. Mechanism of Insect-Borne Transmission Utilizing mosquito nets while sleeping. Infection of the Vector Viral Replication in the Vector Vaccination Transmission to Humans Infection in Humans  Transmission of Viruses Latent Example: Chickenpox virus remains in a dormant state within the host's body after an initial infection, potentially reactivating later to Prevention cause disease Vaccination Mechanism of Latent Transmission Initial Infection Clinical Manifestation Establishment of Latency Reactivation  Classification of Viruses classified based on their nucleic acid structure single-stranded or double-stranded based on nucleic acid composition Double-Stranded RNA (dsRNA) Viruses Single-Stranded RNA (ssRNA) Viruses Retroviruses use reverse transcription to contain segmented RNA convert their RNA genome into Examples: DNA DNA after entering a host cell RNA Positive-Sense RNA (+ssRNA) Viruses nucleic acid structure (single-stranded or Reoviruses: Examples: double-stranded) and the nature of their DNA Rotavirus, a Human translated into proteins (linear or circular) leading cause of Immunodeficiency Virus by the host's ribosomes gastroenteritis in main types: (HIV): Causes AIDS children Double-Stranded DNA (dsDNA) Viruses Examples: Picornaviruses: double-stranded DNA genomes Poliovirus, Rhinovirus Single-Stranded DNA (common cold). (ssDNA) Viruses Examples: Flaviviruses: Hepatitis C, Herpesviruses: Herpes Simplex Virus, Dengue Virus single-stranded DNA Varicella-Zoster Virus. genomes, which can be Adenoviruses: Cause respiratory and Negative-Sense RNA linear or circular gastrointestinal infections. (−ssRNA) Viruses Papillomaviruses: Human Papillomavirus Examples: (HPV), linked to cervical cancer RNA must be Parvoviruses Examples: converted to positive- Orthomyxoviruses: Influenza viruses. sense RNA by an Rhabdoviruses: Rabies virus. RNA polymerase before translation DNA VIRUSES RNA VIRUSES Hepadnaviridae Picornaviridae Flaviviridae Herpesviridae Sedoreoviridae Togaviridae Poxviridae Caliciviridae Retroviridae Papillomaviridae Hepeviridae Orthomyxoviridae Polyomaviridae Filoviridae Paramyxoviridae Adenoviridae Coronaviridae Pneumoviridae Anelloviridae Rhabdoviridae  Examples: Classification of Viruses Bacteriophages: Such as T4 phage, which has an based on capsid morphology icosahedral head and a helical tail used for injecting genetic Icosahedral Viruses material into bacterial Examples: hosts. Adenoviruses: Cause respiratory infections. Poxviruses: Such as Polioviruses: Cause poliomyelitis the smallpox virus, which has a brick-like structure and a Examples: complex surface. Tobacco Mosaic Virus (TMV): A plant virus with a rod-like appearance. Rabies Virus: An animal virus with a helical capsid. Examples: Examples: Adenoviruses: Non-enveloped with an icosahedral shape. HIV (Human Immunodeficiency Virus): An Noroviruses: Non-enveloped viruses that cause gastroenteritis. enveloped retrovirus. Influenza Virus: An enveloped virus with helical  DNA VIRUSES RNA VIRUSES Complex Icosahedral Helical Poxviridae Papillomaviridae Picornaviridae Orthomyxoviridae Polyomaviridae Sedoreoviridae Paramyxoviridae Adenoviridae Caliciviridae Pneumoviridae Anelloviridae Hepeviridae Rhabdoviridae Hepadnaviridae Flaviviridae Filoviridae Herpesviridae Togaviridae Coronaviridae Retroviridae  Classification of Viruses based on presence/absence of outer coat outer lipid membrane (envelope) that surrounds their protein capsid lack an outer lipid envelope and consist solely of the capsid, which encloses the Naked Enveloped viral nucleic acid lipid bilayer that contains viral glycoproteins capsid is made of protein subunits (capsomers) more sensitive to environmental factors, stable and resistant to environmental such as heat, detergents, and desiccation factors like heat, detergents, and desiccation bodily fluids (e.g., blood, saliva) or respiratory droplets contaminated surfaces, food, Examples: water, or through the air Human Immunodeficiency Virus (HIV): Causes AIDS; an enveloped Examples: retrovirus. Adenoviruses: Cause respiratory infections; have an Influenza Virus: Causes seasonal flu; icosahedral structure. has a helical structure and an Noroviruses: Cause gastroenteritis and are often envelope. transmitted through contaminated food and water. Hepatitis B Virus: A liver infection Poliovirus: Causes poliomyelitis; it is highly stable in caused by this enveloped virus. the environment. SARS-CoV-2: The virus responsible Human Papillomavirus (HPV): Associated with warts for COVID-19, which is also and certain cancers; it is also non-enveloped enveloped.  DNA VIRUSES RNA VIRUSES NAKED ENVELOPED NAKED ENVELOPED Papillomaviridae Hepadnaviridae Picornaviridae Flaviviridae Polyomaviridae Herpesviridae Sedoreoviridae Togaviridae Adenoviridae Poxviridae Caliciviridae Retroviridae Anelloviridae Hepeviridae Orthomyxoviridae Paramyxoviridae Pneumoviridae Rhabdoviridae Filoviridae Coronaviridae ENVELOPED VIRUSES NAKED VIRUSES Close contact, Oral-fecal route Sexual intercourse Less stable Stable No cell lysis required in Released by lysis of exiting the cell the host cell Easy target for the host's Less immunogenic immune system  Classification of Viruses based on site of virion assembly Cytoplasmic Nucleic Cytoplasmic assembly: Poxviruses, Togaviruses, Rhabdoviruses Nuclear assembly: Herpesviruses, Adenoviruses, Parvoviruses Mixed sites: Retroviruses, Orthomyxoviruses Membrane-associated assembly: Coronaviruses, Flaviviruses Plasma membrane assembly: Retroviruses, Paramyxoviruses  DNA VIRUSES RNA VIRUSES NUCLEIC CYTOPLASMIC Hepadnaviridae Poxviridae Picornaviridae Orthomyxoviridae Herpesviridae Sedoreoviridae Paramyxoviridae Papillomaviridae Caliciviridae Pneumoviridae Polyomaviridae Hepeviridae Rhabdoviridae Adenoviridae Flaviviridae Filoviridae Anelloviridae Togaviridae Coronaviridae Retroviridae CLASS Genome Site of Replication Example I double-stranded DNA virus Nucleus Adenoviridae, (Except For Poxviridae) Herpesviridae, Poxviridae single-stranded DNA virus II (positive strand/sense) Nucleus Parvoviridae III double-stranded RNA virus Cytoplasm Sedoreoviridae single-stranded RNA virus Picornaviridae, IV (positive strand/sense) Cytoplasm Togaviridae single-stranded RNA virus Orthomyxoviridae, V (negative strand/sense) Cytoplasm Rhabdoviridae single-stranded RNA – VI (positive strand/sense) Cytoplasm Retroviridae reverse transcribing virus double-stranded DNA – VII reverse transcribing virus Nucleus Hepadnaviridae POST-TEST 1. What do you call the protective coat of a virion? 2. Classify Poxviridae based on its site of virion assembly. 3. True or False. Enveloped viruses are heat-resistant because of the protein content of the capsid. 4. What is the Baltimore classification of Hepadnaviridae? 5. Identify the mode of transmission of Zika virus.