lecture #1-2 introduction to microbial pathogens
Post on 22-Dec-2015
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Recent microbes in the news
• Severe acute respiratory syndrome (SARS)
• West Nile virus• Viral or bacterial meningitis• Human immunodeficiency virus (HIV)
• Tuberculosis (drug resistant)
• Cholera and Malaria • Bovine sphongiform encephalitis (Madcow
disease)
• Salmonella
Microbial infection and pathogenesis
Types of microbes
- Bacteria, fungi and protozoa
- Viruses, viroids, prions
Pathogenesis - interactions of molecular events in replication of a microbe and host responses that can result in disease
Microbial infection + immune response = pathogenesis
• Patterns of infection or disease
. acute - short-lived
. persistent - continuous
. latent - reoccurs
. subclinical - carrier state, no symptoms
Unifying concepts for replication and pathogenesis
Microbe structure (eg. morphology, genome type and size, species or variant) • determines how it interacts with- . host or host cells to replicate • . the host immune response
• Knowledge of the interaction of microbe with cells provides insights into:• clinical manifestations of infections and• how to control or interfere with these
Impact of viruses
• Many discovered in the last 20 years
• Viral infections cause estimated 50% of all absenteeism from work and school
• Bacteriophages affect drug resistance and molecular biology eg. restriction enzymes and reverse transcriptase for cloning
• Study as tools to explore biological processes
Three things all microbes must do
– 1 - Make more progeny– 2 - Spread and transmission– 3 - Evade host defenses
• Outcomes of these determine
• pathogenesis
How do these microbes spread?
• Severe acute respiratory syndrome (SARS)
• West Nile virus• Viral or bacterial meningitis• Human immunodeficiency virus (HIV)
• Tuberculosis (drug resistant)
• Cholera and Malaria • Bovine sphongiform encephalitis (Madcow
disease)
• Salmonella
Reservoirs of infectious agents
• Carriers (asymptomatic or subclinical)
• Zoonotic diseases
• Environmental
Transmission
• Modes of transmission to humans
- human to human
- animal to human
- insect to human
• Infection can be localized or systemic
- replicates, remains in local area of entry - replicates, spreads by viremia to other sites
Modes of transmission to or from a host
Sites of microbe entry or shedding
– Respiratory (secretions, aerosols)
– Oral/enteric (food, water)
– Urogenital (sexually transmitted)
– Vectors (insects, needles, animals)
– Contaminated tissues or body products
Some specific modes of virus transmission
Skin infections - for most, skin lesions not significant means of
transmission
- exceptions are HSV in genital herpes, chicken pox from shingles, small pox in dried crusts- infectious for months, up to a year
Respiratory tract infections- transmission in air depends on coughing, sneezing
or infected secretions
Some specific modes of virus transmission (cont.)
Semen• - HIV- much less for CMV, hepatitis B
- Human milk or colostrum• - CMV, HTLV by mother to child • - not a major transmission mode for• hepatitis B, encephalitis viruses, mumps,
rubella
Some specific modes of virus transmission (cont.)
Salivary secretions• - EBV, rabies- rare possibility for CMV, hepB
- Gastroenteric transmission- stools eg. enteric virus, poliovirus, - rotavirus, hepatitis A• - childcare centers, institutions, military camps• - contaminated water from poor waste disposal• - urine is not a major means of transmission
Host factors that affect susceptibility
• age of host• underlying physiological conditions• malnutrition• genetic determinants• gender• environmental conditions
• others eg. stress, personal behavior
Trends in disease• Reduction and eradication of disease
• Emerging diseases
Epidemiology• The study of factors that influence
disease frequency and distribution
Nosocomial infections
• Hospital acquired disease
• Hospitals are reservoirs of infectious agents
• Hospitals enable transmission of infectious agents
• How to prevent nosocomial infections ?
Reservoirs
• Other patients
• Hospital environment
• Health care workers
• Patient’s own normal flora
What procedures are used in dentistry?
Survival strategies of microbes
• Gain entry into host• 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
? Questions to consider
• What is the clinical disease manifestation?• What microbe(s) causes the disease(s)?• How does the microbe enter or leave the host?• What is the target tissue(s) and means of
replication?• Is there damage from replication or immune
response?• What are the disease patterns?• What are the controls, preventions or therapies?• Specific distinguishing features
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