Download Principles of Disease

Principles of Disease
Microbiology 2314
• Every disease is a
race between a
pathogen trying to
gain a foothold and
the host defenses
trying to prevent
the pathogen from
doing so.
Disease
• Is a Process
• Is a State of Being Not In Good Health
• Involves Many Factors
- Age
- Nutrition
- Gender
- Race
• We tend to equate one pathogen with
one disease, but it is more
complicated than that.
• It is actually much more complicated
than that.
Definitions: Parasite
• Refers to Protozoans and Worms
Definition: Pathogen
• Refers to Bacteria / Virus / Fungus
• An organism with the potential to cause
disease.
More Definitions:
• Infection
A pathogen growing in or on the host
• Virulence
The degree or intensity of pathogenicity
• Invasiveness
Ability to spread to other tissues
• Infectivity
Ability to secrete toxins
• Septicemia
Blood infection
• Pathology
Scientific study of disease
• Etiology
Cause of disease
• Pathogenesis
Development of disease
• Host
Organism that shelters and
supports the growth of
pathogens.
Disease
• An abnormal process in which part or all
of the body is not properly adjusted or is
incapable of performing normal functions
often because of infection by pathogens.
Relationships Between
Microorganisms and Man
Usually germ-free in utero
Microorganisms begin
colonization in and on the
surface of the body during and
after birth
We require these organisms
David Vetter the
“Bubble Boy”
Germ-free organisms are less
healthy than organisms with
normal microbiota
Body Regions Have Characteristic
Flora
• Skin
• Mouth
• GI Tract
1012
1010
1014
Normal Flora Are Found Mostly
–
–
–
–
–
–
–
–
•
on the skin
in the eyes
in the nose
in the mouth
in the upper throat
in the lower urethra
in the lower intestine
especially in the large intestine
Note that this list basically includes all of the body surfaces
exposed to the external environment.
Microbial Antagonism
• Normal Microbiota establish permanent colonies
inside or on the body without producing disease
• Symbiosis
• Three Types
1. Commensalism
2. Mutualism
3. Parasitism
• Transient microbiota are members of the normal flora
that are not always present or are present for only a few
days, weeks, or months before disappearing.
Nitrogen Fixation -- Mutualism
Ruminants and Resident Microbes
– Mutualism
Lichen Symbiosis
-- Mutualism
Ascaris Worms /
Parasitism
• The upper respiratory tract consists of the
nostrils, nasal cavities and throat. It contains a
number of commensalistic inhabitants
including: Staphylococcus epidermidis.
Out of all types of symbiotic
bacteria, commemsalists are
the least studied.
The reason for this is
simple; if a bacteria is not
causing harm or benefit to a
host there is simply not
much reasons to studying it.
Microbial Antagonism
Microbial Antagonism or Colonization inhibition: A process
by which pathogenic microorganisms are inhibited by normal flora
from colonizing healthy organisms (a form of symbiosis)
Antagonism between the
fungus Paraconyothyrium
variabile and Fusarium
oxysporum
• Mechanisms by which this inhibition
occurs includes:
1. competing with pathogenic microorganisms
for nutrients
2. competing with pathogenic microorganisms
for space
3. producing toxins that are harmful to some
pathogenic microorganisms
Remember!
• Categorizing symbiotic relationships is
convenient, but keep in mind that under
certain circumstances the relationship can
change.
Question?
•
A colonic microorganism which bores into its
host and by doing so does it damage, competes
with its host for nutrients, but is the sole
supplier of an organic growth factor without
which the host could not survive. This symbiotic
relationship is an example of (chose the best
answer):
a. commensalism
b. mutualism
c. parasitism
Question?
•
A colonic microorganism which bores into its
host and by doing so does it damage, competes
with its host for nutrients, and is the sole
supplier of an organic growth factor without
which the host could not survive. This symbiotic
relationship is an example of (chose the best
answer):
a. commensalism
b. mutualism
c. parasitism
Question?
• A bacteria is attached to the intestinal wall
via its pili, causes its host no harm, and
secretes an antibacterial poison which limits
colonization of the intestine by other,
unrelated bacteria. With regard to the
prevention of disease, what process
specifically is this bacteria effecting?
Microbial Antagonism
Question?
•
Microbial antagonism (choose best answer)
a. is a parasitic interaction between two
organisms
b. describes generally the harm done by a
microorganism to a host
c. can be an example of mutualism
d. can be an example of parasitism
e. all of the above
Ab. none of the above
Question?
•
Microbial antagonism (choose best answer)
a. is a parasitic interaction between two
organisms
b. describes generally the harm done by a
microorganism to a host
c. can be an example of mutualism
d. can be an example of parasitism
e. all of the above
Ab. none of the above
Question?
•
A colonic microorganism which bores into its host and
by doing so does it damage. This organism has no
additional redeeming characteristics. You would
describe the symbiotic relationship it has with its host as
an example of (choose the best answer):
a. commensalism
b. mutualism
c. microbial antagonism
d. parasitism
e. none of the above
Question?
•
A colonic microorganism which bores into its host and
by doing so does it damage. This organism has no
additional redeeming characteristics. You would
describe the symbiotic relationship it has with its host as
an example of (choose the best answer):
a. commensalism
b. mutualism
c. an effector of microbial antagonism
d. parasitism
e. none of the above
Question?
•
Which is not a member of the normal flora of a
plant or an animal? (assume all are obligate
colonizers of the plant or animal host organism)
a. a bacterium
b. a virus
c. a fungus
d. a protozoa
e. all are equally likely to be members of
normal flora
Question?
•
Which is not a member of the normal
flora of a plant or an animal?
a. a bacterium
b. a virus
c. a fungus
d. a protozoa
e. all are equally likely to be members
of normal flora
Question?
• Name a part of the body that you would not
expect to have an associated normal flora.
Stomach
Kidney
Liver
Etc.
Anything Basically That Is Internal
Transient Microbiota
• Transient microbiota are members of the normal
flora that are not always present or are present for
only a few days, weeks, or months before
disappearing.
Opportunistic Microorganisms
• Do not cause disease under normal conditions but
can cause disease under special conditions.
Staph Infection
Cooperation Among
Microorganisms
• One of the organizing principles of life on
Earth is that cells cooperate.
• This is evident in the case of multicellular
organisms, from nematodes to humans, but
it also appears to apply widely among
single-celled organisms such as bacteria,
fungi, and amoeba.
• A well-studied example of intraspecies
cooperation concerns the cyanobacterium
Anabaena, which grows in long chains, in
which approximately one cell out of ten
differentiates into a heterocyst that provides
fixed nitrogen for the neighboring cells
This Cellular Cooperation Can
Increase the Virulence of a
Microorganism
Example:
Strep Infection  Scarlet Fever  Rheumatic Fever
The Etiology of Infectious Disease
Koch’s Postulates
• Robert Koch played an
important role in
determining that
specific microbes were
associated with specific
diseases.
• Four Postulates
1. Same pathogen
must be present in
every case of the
disease.
2. Pathogen must
be isolated in pure
culture.
3. Pathogen
isolated from pure
culture must cause
the same disease
in lab animal.
4. Pathogen must
be re-isolated
from inoculated
lab animal.
Exceptions to Koch’s Postulates
• Inability to grow on artificial media (Syphilis)
Exceptions to Koch’s Postulates
• Unequivocal signs and symptoms (Tetanus)
Exceptions to Koch’s Postulates
• Diseases caused by
variety of
organisms
(Pneumonia)
• Pathogens causing
variety of diseases
(Streptococcus
pyogenes)
Exceptions to Koch’s Postulates
• Diseases that occur in humans only (Smallpox)
Classifying Infectious Diseases
• Symptoms
Subjective Changes
Cannot Be Measured
• Signs
Objective Changes
Measurable Changes
Sign or Symptom?
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•
•
•
•
•
Pain
Temperature
Nausea
Swelling
Discomfort
Blood Pressure
Classifying Infectious Diseases
• Syndrome
A specific group of symptoms or signs
that always accompany a specific disease.
What is the Syndrome?
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•
Flu
Measles
Anthrax
Legionnaires
Mumps
Carbuncles
Smallpox
West Nile Virus
Communicable Diseases
• Transmitted Directly or Indirectly From
One Host to Another Host
Chickenpox
Measles
Genital Herpes
Contagious Diseases
• A communicable disease that is spread
easily from one individual to another
Name a Communicable Disease that
is Not Contagious.
Noncontagious Diseases
• Caused by microorganisms that normally grow outside the
human body and are not transmitted from one host to
another.
Tetanus
Anthrax
The Occurrence of Disease
• Incidence
Number of New Cases of Disease in a
Given Population.
The Risk of Disease
• Prevalence
Number of Existing Cases of Disease in
a Given Population at Any One Time
The Burden of Disease
Question?
• Assume a classroom of 50 students exposed to a
new strain of three-day influenza.
• Before exposure, the prevalence and incidence in
this population are both zero.
• If within one week, 5 out of the 50 students
contract the flu, what is the incidence?
• What is the prevalence for that one week period?
Continue?
• If after one more week, 5 more students become
infected, what is the point prevalence?
• What is the overall prevalence?
• What is the incidence?
Trends
• Changes in incidence and prevalence are usually
followed over a seasonal, yearly, and long-term
basis and are helpful in predicting trends.
• Statistics of concern to epidemiologists are the
rates of disease with regard to sex, race, and
geographic region.
What We See
• Infectious Diseases
High Incidence
Low Prevalence
• Chronic Diseases
Low Incidence
High Prevalence
Classification of Disease
• Sporadic
Only an Occasional Case (Typhoid Fever)
• Endemic
Constantly Present at an Expected Level
(Common Cold)
• Epidemic
Above the Normal Expected Frequency (Flu)
• Pandemic
World Wide Epidemic (AIDs)
Scope of Disease
• Acute
Develops Rapidly
Short Lifespan
Usually Severe Symptoms
Example: Flu, Measles
• Chronic
Develops Slowly
Continual, Long Lasting, or Reoccurring
Usually Less Severe
Example: Osteoporosis
• Latent
Causative Agent Remains Inactive for a
Time – Then Becomes Active and
Produces Symptoms.
Chicken Pox to Shingles
HIV to AIDS
Herd
Immunity
• The presence of
immunity to a
disease in most of
the population.
• Normally due to
Vaccination.
Herd Immunity is the Reason we
Vaccinate!
The way herd immunity works is by isolating potential hosts and
reducing virus’ opportunities to be passed on. For herd immunity to
be effective I need to vaccinate at least 90% of the susceptible
population.
If I drop below a 90% vaccination rate, the chances of passing
infection increase and I get small clusters of disease occurring.
Emerging Infectious Diseases
•
New diseases with increasing incidence.
1. SARS
2. Ebola
3. West Nile Virus
4. Bird Flu
5. Monkeypox
Emerging Infectious Diseases
EIDs
• EIDs Can Result From
1. Overuse of Antibiotics
2.
3.
4.
5.
Overuse of Pesticides
Climatic Changes
Travel
Lack of Necessary Vaccinations
The CDC, NIH and WHO are responsible for surveillance and
responses to EIDs and the world’s health.
Re-emerging Infectious Diseases
RIDs
• Old diseases that are occurring with
increasing incidence.
1. Tuberculosis
2. Hantavirus
3. Plague
The Extent of Host Involvement
Local Infection
• A local infection
affects a small area of
body
• Boil or Acne
Systemic Infection
• Infection spread
throughout the
body via the
circulatory system
• Mumps
• Systemic Infections
often lead to Focal
Infections.
• What is a Focal
Infection?
Secondary Infection
• After the host is
weakened from a
primary infection, it
is easier for them to
become infected
with a secondary
infection due to a
compromised
immune system.
Unapparent or Subclinical Infection
• An apparently
healthy individual
carries the disease
organism and
passes it on to
others without
expressing any
symptoms of the
illness.
• Poliovirus
• Hepatitis A
• HIV
Reservoirs of
Infection
For a disease to
perpetuate itself,
there must be
continual
organisms
available and a
source providing
appropriate
conditions.
Birds are Reservoirs for WNV
• Marine shellfish are the main reservoir of Cholera
Zoonoses
• Diseases that affect wild and domestic
animals and can be transmitted to humans.
• Lyme Disease
• Rabies
• Anthrax
• West Nile Virus
Transmission of Zoonoses
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Direct Contact with Infected Animals
Direct Contact with Animal Waste
Contamination of Food and Water
Contaminated Hides, Fur, and Feathers
Consuming Infected Animal Products
Insect Vectors
Some Diseases Result from Pathogenic
Microorganisms Growing in or on
Nonliving Reservoirs Such as Soil and
Water or Objects
• Ringworm
• Botulism
• Tetanus
Transmission of
Disease
• Direct Transmission
1. Close Personal Contact
2. Touching, Kissing, etc.
Indirect Transmission
1.
2.
3.
4.
Fomites
Droplets/Airborne
Vehicles
Vectors
Direct Transmission
1. Personal Contact
2. Touching
Kissing
Sex
Etc.
Indirect Transmission
• Fomites
Inanimate Objects
Tissues, Drinking Glasses, Needles
AIDS, Hepatitis
Indirect Transmission
• Transmission by a Medium
Water, Food, Air
Plague, Cholera
Indirect Transmission
• Droplet Transmission
Saliva and Mucus
Coughing, Sneezing, Laughter
Less than 1 Meter
Indirect Transmission
• Airborne Transmission
Carried on Water/Mucus Droplets
Greater than 1 Meter
Indirect Transmission
• Vectors (Often Arthropod)
1. Mechanical Means
Passive Process
Pathogens are on the body of the vector.
Ex. Fly landing on food
Can you name a Disease
Transmitted by this
Process?
this
Indirect
Transmission
• Vectors (Often
Arthropod)
2. Biological Means
Active Process
Vector must bite
or scratch or sting.
Ex. Mosquito Bite
Can you name a
Disease Transmitted
by this process?
Routes of Transmission
1. Vertical
Mother to Offspring
- Transplacental: Rubella, Toxoplasma
(Note: Humans only have two layers of separation)
- Perinatal: Listeria, Gonorrhea, Chlamydia
- Breastfeeding: HIV
2. Horizontal
Person to Person
- Contact Spread
- Common Vehicle
- Airborne
- Vector-borne
Portals of Exit (Preferred Ways to Leave
the Body and Spread Infection)
• Respiratory Tract
(Coughing or Sneezing)
• Gastrointestinal Tract
(Saliva or Feces)
• Urogenital Tract
(Secretions from the
Vagina or Penis)
Arthropods and
Syringes provide a
portal of exit for
microbes in blood.
Nosocomial Infections
• An infection that is
acquired during the
course of stay in a
health facility.
• 2 million NI Yearly
• 5-15% of All
Patients Acquire NI
• 90,000 Die
The Rate of Nosocomial Infections Is
Increasing
Trends in Nosocomial Infections
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•
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•
•
1940’s – 1950’s
1970’s
1980’s
1990’s
2000’s
Gram + S. aureus
Gram – E. coli
Gram + A.R. S. aureus
Both
No Relief in Sight
Frequency of Nosocomial
Infections
Large Number of Skin Infections Due to Newborns
The Compromised Host is Most
at Risk
1. Burns (Broken Skin)
2. Surgical Wounds
(Broken Skin)
3. Suppressed Immune
Systems (Due to Ill
Health)
The Body Defends Us
• Skin and Mucus Membranes
• T-Lymphocytes Kill Pathogens
• B-Lymphocytes Produce Antibodies
• Their Effectiveness if Altered By Many Things
-
Drugs
Radiation
Steroids
Burns
Diabetes
Stress
Poor Nutrition
Chain of Transmission:
Nosocomial Infections Are Transmitted
By Direct Contact Between Staff
Members and Patients
Fomites such as
catheters, syringes, and
respiratory devices can
transmit nosocomial
infections.
Control of Nosocomial Infections
1. Handwashing #1
2. Disinfect Equipment
3. Necessary Antibiotics Only
4. Infection Control Team
Could a copper door handle help
to beat MRSA (2009 Study)?
• Doorknobs, bath taps, toilet handles and 'grab
rails' will be ripped out and replaced with
copper versions at Birmingham's Selly Oak
hospital in a bid to beat MRSA
• MRSA has proven resistant to even the most
powerful antibiotics. But hospital superbugs
may finally have met their match - in copper
door handles.
• Copper, used in medicines for 4,000 years,
has been shown to be highly effective in
killing off pathogens such as MRSA.
• In the trial study, copper grew 95% less
bacteria.
Predisposing Factors
A Factor that Makes the Body More Susceptible
to Disease or Alters the Course of an Illness.
•
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Gender
Climate
Age
Fatigue
Poor Nutrition
Low Vitamin D
Epidemiology
• The study of the distribution and
determination of health related events
within a given population.
• The study of the transmission, incidence,
and frequency of disease
1. Descriptive Epidemiology
2. Analytical Epidemiology
3. Experimental Epidemiology
Descriptive Epidemiology
• Data about infected people are collected and
analyzed in descriptive epidemiology.
• Who, What, When, Where, How, etc.
Analytical Epidemiology
• A group of infected people is compared with an
uninfected group.
• Analytical epidemiology aims to research and
study risk and protector factors of diseases.
Relative Risk of Death on the
Titanic
Female
Male
Alive
Dead
308
154
462
142
709
851
Female
Male
Alive
Dead
308
154
462
142
709
851
Probability of Death for Females is 154 / 462 = .333 or 33%
Probability of Death for Males is 709 / 851 =.833 or 83%
RR = .833 / .333 = 2.5
There is a 2.5 greater probability of death for males than for
females.
Experimental Epidemiology
• Use of controlled experiments designed to test
hypotheses are performed in experimental
epidemiology.
• Example: In these studies normal guinea pigs
were exposed to tuberculosis cage mates in two
different degrees of crowding, some in ordinary
cages, where the food became contaminated with
the excreta, laden with tubercle bacilli, of the
inoculated animals, and some in special cages with
wire-mesh floors, where these excreta were
largely excluded as a source of contagion.
Clinical Trial
History
• John Snow
• London Cholera
Epidemic
• Broadstreet Pump
The CDC is the Main Source of
Epidemiological Information in the
United States