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Lecture-1 Introduction to Virology.pptx

  1. PRINCIPLES OF VIROLOGY (BSC-401) Instructor: Fahed Parvaiz, Ph.D CAS-PIFI Fellow Post-Doc (Virology & Immunology)
  2. Introduction to virology • Viruses are ubiquitous on earth. • Infect all cellular forms i.e. Prokaryotes and Eukaryotes. • Upon infection…typical symptoms. • Some viruses are non-pathogenic. • Some are active while some are in quiescent phase. • Some contain remnants of host genomes
  3. What is a virus? 1) Submicroscopic, obligate intracellular parasite. 2) Particles are produced from assembly of pre-formed components. 3) Virus particles (virions) themselves do not grow or undergo division. 4) They do not encode information for: a- energy production b- ribosomes c-tRNAs (a few exceptions) d- lipid membrane synthesis
  4. Virus diversity: From the beautiful…. Three Broken Tulips By Nicolas Robert (1624-1685) Striping patterns on tulips caused by tulip mosaic virus infection.
  5. …to the down right nasty! Smallpox lesions in a child
  6. This knowledge permits the development of effective means for prevention, diagnosis and treatment of virus diseases through the production of vaccines, diagnostic reagents and techniques, and antiviral drugs. These medical applications therefore constitute major aspects of the science of virology.
  7. • Important factors to be studied in virology: i. Nature ii. Gene expression (Transcription and Translation) iii. Mode of replication iv. Cellular internalization v. Interaction with host cellular factors/ proteins vi. Host defense mechanisms vii. Mechanism of pathogenesis viii. Virus egress
  8. Other areas of virology • Veterinary virology and plant virology are also important because of the economic impact of the many viruses that cause disease in domestic animals and crop plants: foot and mouth disease virus and rice yellow mottle virus are just two examples. • Another area where viruses can cause economic damage is in the dairy industry, where phages can infect the lactic acid bacteria that are responsible for the fermentations that produce cheese, yogurt and other milk products.
  9. Virus: A beneficial creature 1. Phage typing of bacteria 2. Enzyme production 3. Pesticides 4. Anti-bacterial agents 5. Anti-cancer agents 6. Gene vectors
  10. 1. Phage typing of bacteria • Some groups of bacteria, such as Salmonella species, are classified into strains on the basis of the spectrum of phages to which they are susceptible. • Identification of the phage types of bacterial isolates can provide useful epidemiological information during outbreaks of disease caused by these bacteria.
  11. 2. Enzyme production A number of enzymes used in molecular biology are virus enzymes.  Examples: Reverse transcriptase from retroviruses. RNA polymerases from phages
  12. 3. Pesticides  Some insect pests are controlled with baculoviruses and myxoma virus.
  13. 4. Anti-bacterial agents • Initially, bacteriophages were harvested for the treatment of bacterial infections. • Discovery of Antibiotics & eventually emergence of drug resistant bacterial strains. • Bacteriophages.
  14. 5. Anti-Cancer agents • Genetically modified strains of viruses, such as herpes simplex virus and vaccinia virus, are being investigated for treatment of cancers. • These strains have been modified so that they are able to infect and destroy specific tumour cells, but are unable to infect normal cells.
  15. 6. Gene vectors for protein production • Viruses such as certain baculoviruses and adenoviruses are used as vectors to take genes into animal cells growing in culture. This technology can be used to insert into cells genes encoding useful proteins, such as vaccine components, and the cells can then be used for mass production of the proteins.
  16. Addgene, Repository for Vectors
  17. Nature of viruses • Microscopic particles • Contain genes • Parasites
  18. 1) Viruses are microscopic particles • Evidence for the existence of very small infectious agents was first provided in the late 19th century by two scientists working independently: Martinus Beijerinck in Holland and Dimitri Ivanovski in Russia. They made extracts from diseased plants, which we now know were infected with tobacco mosaic virus, and passed the extracts through fine filters. The filtrates contained an agent that was able to infect new plants, but no bacteria could be cultured from the filtrates. The agent remained infective through several transfers to new plants, eliminating the possibility of a toxin. Beijerinck called the agent a ‘virus’ and the term has been in use ever since.
  19. • Mainly measured in nm. • Smallest group of viruses include parvoviruses (20nm). • Virology concerns with smallest yet among diverse group of microbes.
  20. 2) Viruses contain genes • Considered to be living primarily because of: DNA/RNA and its replication. • Mainly four different possibilties: • double-stranded DNA • single-stranded DNA • double-stranded RNA • single-stranded RNA.
  21. • Genome: The genomic content of the virus together makes up its genome. • Capsid: The viral coating that protects its genome and helps in the host viral interaction is known as capsid. • Virion: The combination of viral genome, capsid and other replication machinery together constitute Virion.
  22. Viruses are extensively tiny yet favor pathogenesis. How? • There are several mechanisms: i. Harboring host cell proteins ii. Efficient coding iii. Multifunctional proteins
  23. i. Harboring host cell proteins The genomes of large viruses duplicate some of the functions of the host cell, but the small viruses rely very heavily on functions of the host cell.
  24. ii. Efficient coding There may be overlapping genes and genes encoded within genes. The small genome of Hepatitis B virus is a good example
  25. iii. Multifunctional proteins A virus protein may have several enzyme activities.
  26. 3. Viruses are parasites Viruses differ from cells in the way in which they multiply. A new cell is always formed directly from a pre-existing cell, but a new virion is never formed directly from a pre-existing virion. New virions are formed by a process of replication, which takes place inside a host cell and involves the synthesis of components followed by their assembly into virions.
  27. Contd… • 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 nucleotides. 2. Protein-synthesizing machinery (ribosomes). 3. Energy, in the form of Adenosine triphosphate.
  28. Contd… A virus modifies the intracellular environment of its host in order to enhance the efficiency of the replication process. Modifications might include production of new membranous structures, reduced expression of cell genes or enhancement of a cell process. Some large phages encode proteins that boost photosynthesis in the cells of their photosynthetic bacterial hosts, thereby probably boosting the yields of virus from the cells
  29. “There is nothing so patient, in this world or any other, as a virus searching for a host.” Mira Grant