Transcript PowerPoint Presentation - Unifying problems all viruses

Lecture #1-2
Introduction to Microbial
Pathogens
Fig 20.1.
Community water supply in a developing country
Recent microbes in the news
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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
Figs 1.5, 1.7, 1.9
Figs 1.10 and 1.11
Microbial infection + immune
response = pathogenesis
• Patterns of infection or disease
. acute - short-lived
. persistent - continuous
. latent - reoccurs
. subclinical - carrier state, no symptoms
Table 20.1
Common terms in epidemiology
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
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. 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
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- Make more progeny
- Spread and transmission
- Evade host defenses
• Outcomes of these determine
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pathogenesis
Fig 20.1
Spread of
pathogens
How do these microbes spread?
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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
Fig. 20.01a
Reservoirs
harbor
potentially
pathogenic
microbes
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
Fig. 20.01b
Modes of
transmission
of microbes
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
Fig. 20.01c
Portals of
entry
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
Figure 20.3
Air bourne transmission
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
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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
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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
Fig. 20.08
National and
worldwide
surveillance
of infectious
diseases is
critical
Fig 20.9
Child with
smallpox,
an
eradicated
disease
(polio,
bubonic
plague)
Fig. 20.09
Fig 20.10
World Map of Emerging Diseases
Nosocomial infections
Figure 20.11
Fig. 20.12
Nosocomial infections
• Hospital acquired disease
• Hospitals are reservoirs of infectious
agents
• Hospitals enable transmission of
infectious agents
• How to prevent nosocomial infections ?
Reservoirs
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Other patients
Hospital environment
Health care workers
Patient’s own normal flora
What procedures are used in dentistry?
Survival strategies of microbes
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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
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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