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Prevention and control of microbial infections

Prevention and control of microbial infections. Domitory 2222 Department of medicine From Shandong university. Prevention and Control of Microbial Infection . Interaction of microbes with host immune system determines - outcome of an infection and disease

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Prevention and control of microbial infections

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  1. Prevention and control of microbial infections Domitory 2222 Department of medicine From Shandong university

  2. Prevention and Control of Microbial Infection Interaction of microbes with host immune system determines - outcome of an infection and disease - ways to control those infections - effects on populations

  3. Three things all viruses must do 1 - Replicate to make progeny 2 - Spread and transmission • - Evade host defenses

  4. 3. Evade host defenses • Evade anti-viral defenses • Struggle between virus and host • Virus must evade long enough to replicate and transmit, or establish latent or persistent infection • Disease is unintended consequence of how a virus solves three problems

  5. Types of Prevention and Control • Natural defenses • Host immune defenses • Vaccines- prevent viral infection • Antiviral chemotherapy- reduce viral • disease after infection

  6. Types of host defenses • Natural barrier defenses • Innate defenses (phagocytes, complement, interferon, NK ) • Adaptive immune defenses (antibodies, NK cell)

  7. Natural host defenses - defend against a variety of microbes - include • skin epidermis layer • pH and enzymes of stomach • ciliation of respiratory tract • mucosal surfaces • blood brain barrier

  8. Activation of immune response • Natural barrier is breached • Innate immune system quick response (complement and macrophages) (natural killer, neutrophils, monocytes) • Cytokine activation eg. TNF, IFN-g • Dendritic cells communicate to adaptive system by migrating to lymph node

  9. Adaptive host defenses • Humoral immunity • antibody mediated immune responses • antibodies, IgA, IgM, IgG • interferons • Cellular immunity • cytotoxic T-cells lyse infected cells • Interferons and other cytokines

  10. Weaknesses of immune defenses • Innate - recognizes bacteria better than viruses - some viruses sneak past host detection • Adaptive - specific but slow to react - less efficient in infants and aged

  11. Preventions and controls: Vaccines • Prime immune response without causing actually viral disease • Properties of viral vaccines • given usually before disease encounter • can be given once or repeated • can vary in protection

  12. Historical perspective • Vaccine success stories • smallpox, yellow fever, measles, rubella • Criteria for eradication • - no animal reservoire • - effective vaccine available • - one stable virus strain • - easily recognizable disease • - infection provides lifelong immunity

  13. Vaccine types • Usually provided before infection • Live attenuated • adenovirus,measles,rubella • Killed • influenza,rabies,cholera • Subunit vaccines • hepatitis B ,tetanus

  14. Prevention and controls: Anti-virals • Goals of chemotherapy • - reduce severity of disease • - specifically interrupt events unique to • replication of virus • - do not adversely affect the host

  15. Anti-viral considerations - give after or during infection - selective toxicity - defined target site - side effects - duration and range of effectiveness - development of resistance - economical market

  16. Some current anti-virals • Ribavirin (virazole) • Amantadine (adamantanamine) • Azidothymidine (AZT) • WIN 51711 (Disoxaril) • Ganciclovir (DHPH)

  17. Viral survival strategies • Gain entry • Multiply at local site • Find suitable niche • Overcome or subvert host defenses - outrun - antigenic change - hide in host - mimic host component - inactivate/down-regulate host response

  18. How to determine that a virus causes a certain disease: Koch’s postulates • Microbe must be associated with infectious disease • Isolate virus from diseased host and prepare a pure culture • Inoculate pure culture into healthy host who becomes sick with the same disease • Isolate the same microbe from the new sick host

  19. Koch’s molecular postulates • Gene or factor should be associated with pathogenic condition or phenotype • Inactivate or alter this gene should lead to measurable decrease in virulence or pathogenicity • Specifically replace gene should restore virulence

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