Prevention and control of microbial infections
Domitory 2222Department of medicine
FromShandong university
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
Three things all viruses must do
1 - Replicate to make progeny2 - Spread and transmission3 - Evade host defenses
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
Types of Prevention and Control
• Natural defenses
• Host immune defenses
• Vaccines- prevent viral infection
• Antiviral chemotherapy- reduce viral
disease after infection
Types of host defenses
• Natural barrier defenses• Innate defenses
(phagocytes, complement, interferon, NK )
• Adaptive immune defenses(antibodies, NK cell)
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
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-• Dendritic cells communicate to adaptive
system by migrating to lymph node
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
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
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
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
Vaccine types• Usually provided before infection
– Live attenuated
adenovirus,measles,rubella
– Killed
influenza,rabies,cholera
– Subunit vaccines
hepatitis B ,tetanus
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
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
Some current anti-virals
– Ribavirin (virazole)– Amantadine (adamantanamine)– Azidothymidine (AZT)– WIN 51711 (Disoxaril)– Ganciclovir (DHPH)
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
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
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