Basic Characteristics of Viruses (Students Copy) PDF

What are Viruses? Viruses are infectious, obligate intracellular parasites made up of genetic materials (DNA or RNA), covered by a protein coat, at times a membrane e.g. Corona virus has membrane surrounding the nucleic acid   Virus exist before cells on the planet...

What are Viruses? Viruses are infectious, obligate intracellular parasites made up of genetic materials (DNA or RNA), covered by a protein coat, at times a membrane e.g. Corona virus has membrane surrounding the nucleic acid   Virus exist before cells on the planet  Viruses live everywhere  We eat and breathe billions of virus particles  Virus infect all living things  We carry viral genomes as part of our We live in a own genetic materials Cloud of  Viruses are necessary evils in our lives Viruses!  Viruses are not just messenger of bad Polyomavirus news (most do not carry any disease e.g. Polyomavirus)  DNA-Polyomavirus (family virus)aid tracking of human migration (from Africa, America, Asia, Australia, Europe)  Fundamentals of Viruses Are Viruses Living?  Virus amaze the learned and frighten unlearned  Virus is not a living thing, it do not think  Virus is a passive agent of infection  Virus is a chemical reacting to its environment  Virus is an organism with dual phases  Virion (infectious particle)  Infected host living cell  Fundamentals of Viruses Are Viruses Production by Replication or Binary fission? Virus replicate only in the host cell and assemble its pre-formed particles Whereas binary fission is famous among bacteria  Polyomavirus Welcome to the lecture on Virus. I trust you will all enjoy listening to me Basic Characteristics of Viruses Viruses are microscopic (100-1,000 smaller than humans' cells), infectious agents which replicate inside living host cells Characteristics 1. Non-living: They lack ability to carry out metabolic processes They do not have cells They can not produce energy They do not grow or respond to stimuli 2. Genetic material: They contain either DNA or RNA Their DNA/RNA protected by capsid (protein coat) Few viruses are protected by host cell membrane 3. Intracellular parasites: They are obligate parasite (depend on host cells to replicate and reproduce) They reproduce using host cells mechanism to make copies of themselves 4. Specificity: They infect specific host cells Each virus has specific range of host species Each virus target specific cell types 5. Reproduction: They attach to host cells penetrate host cells membrane replicate viral genetic particles assemble new viral particles release new viral particles from the host cell can not replicate outside the host cell 6. Disease-causing: Many are pathogenic They cause diseases in humans, animals, plants, bacteria Examples Flu Common cold HIV/AIDS Hepatitis COVID-19 7. Variability: Viruses have high mutation rates and genetic recombination Variability impact effectiveness of vaccines and antiviral treatments 8. Immune response: Host cells antibodies immune cells to neutralize the virus and clear infection Vaccine stimulate immune system to produce specific antibody against virus without causing disease Summary: Knowledge of characteristics of viruses is vital for developing strategies to prevent and control viral infection. Mitigation of the spread of viruses include development of vaccine, antiviral drugs and public health measures Classification of Viruses (Baltimore criteria) Virus classification is based on the following: Core content Shape Mode of replication Phenotypic characteristic Chemical composition Capsid structure Size Core content of virus Single-stranded (ss) DNA viruses Picornavirus Picornavirus Parvovirus Parvovirus Double-stranded (ds) DNA viruses Adenovirus Herpes virus Adenovirus Herpes virus Core content of virus Double-stranded (ds) RNA viruses Reovirus Reovirus Single-stranded (ss) RNA viruses  +RNA  -RNA Human Poliovirus Hepatitis A virus Examples Hepatitis A virus Influenza virus Poliovirus Rabies virus Dog Rabies virus Influenza virus Structure of virus Classification based on different shapes and symmetry of viruses are as follows: Complex virus. Poxvirus Radial symmetry virus. Bacteriophage Cubical or icosahedral symmetry shaped virus. Reovirus, Picornavirus Rod or Spiral shaped or helical symmetry virus. Paramyxovirus, orthomyxovirus Virus Classification based on replication site Host cell Virus Virus Organelle type Cytoplasm All RNA Except Influenza Nucleus & All RNA Influenza, Pox virus Cytoplasm Nucleus All DNA Except Pox virus Virus double- All DNA Retrovirus, Tumor RNA stranded DNA intermediate Virus single- All RNA Except Reovirus, Tumor RNA stranded RNA intermediate Classification of Virus based on Host Host Virus type Virus Type Animal Animal Influenza, Mumps, Rabies, cells Poliovirus, Herpes Plant Plant obligate Potato virus, Tobacco mosaic cells virus (TMV), Beet yellow virus, Cauliflower mosaic virus Bacterial Bacteriophage DNA virus, MV-11, RNA virus cells Insect Insect Ascovirus virions, Entomopox cells (biocontrol agent) virus  Classification virus based on Mode of Transmission Source of Route of Common virus transmission transmission Airborne Respiratory Swine, Rhinovirus tract Contaminated Fecal oral route Hepatitis A virus, water/food Poliovirus, Rotavirus Sex Sexual organs Retrovirus, Human papillomavirus Blood Blood Hepatitis B virus, Human transfusion Immunodeficiency Virus (HIV) Insect (Zoonoses) Bite Rabies virus, Alpha virus, Flavivirus, Ebola virus MANY THANKS FOR YOUR FOCUSED ATENTION