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Pathology & Concerns
Pathology - scientific study of disease
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Etiology - the cause of disease
Pathogenesis - the manner in which the disease develops, changes
caused by the disease and the final effects on the body
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Infection & Disease
Normal Microorganisms
Normal microbiota (flora): microorganisms which colonize the body,
but do not produce disease under normal circumstances (those which
are present, but only temporarily, are transient microbiota)
Infection - invasion or colonization of the body by pathogenic
microorganisms
Normal microbiota can prevent disease or overgrowth of harmful
organisms through competition - called microbial antagonism
this differs from…
This can be direct competition for nutrients, or through production of
bacteriocins, proteins which inhibit other bacteria of similar species
Disease - when an infection causes a change from the normal state of
health
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Microorganisms and Disease
Opportunism
Symbiosis - the host and microbiota living together
Opportunistic pathogens are organisms which do not normally cause
disease in a healthy person, but will cause disease if the person is
weakened
This can occur in several formats…
Commensalism - one benefits and the other isn't harmed
for example, from previous disease, or immunosuppression such as
cancer therapy
Mutualism - both benefit
Parasitism - host is harmed
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Etiology
Determined via Koch's postulates
1. The same pathogen must be present in every case of the disease.
2. The pathogen must be isolated from the diseased host and grown in
pure culture.
3. The pathogen from the pure culture must cause the disease when it is
inoculated into a healthy, susceptible laboratory animal.
4. The pathogen must be isolated from the inoculated animal and must
be shown to be the original organism.
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Unculturable Organisms
Modifications to Koch's Postulates necessary for unculturable diseases.
Can use molecular methods or compare cultures from different
specimens (mouse, guinea pig etc…) for intracellular parasites
eg.
Treponema pallidum (syphilis)
Mycobacterium leprae (leprosy)
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Classifying Infectious Diseases
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Classifying Infectious Diseases
Symptoms - subjective changes in body function (pain, malaise - not
easily measurable)
Communicable disease - disease which spreads from one host to
another (ex. genital herpes)
Signs - objective changes that can be observed and measured (eg.
lesions, fever, etc.)
Contagious disease - disease which spreads easily from person to
person (ex. chickenpox)
Syndrome - a group of symptoms or signs which may always
accompany a particular disease.
Noncommunicable disease - not spread from host to host
(eg. opportunistic infections caused by normal flora, or disease such as
tetanus introduced from outside the body)
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Frequency of Disease
Occurrence of Disease
Incidence - the fraction of a population that contracts the disease
during a particular time period
Sporadic - occurs only occasionally
Prevalence - fraction of a population having the disease at a specified
time.
Endemic - constantly present
Epidemic - many people in a given area acquire a certain disease in a
relatively short time period.
Pandemic - worldwide epidemic
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Severity & Duration of Disease
Emerging Infectious Diseases
new or changing diseases showing an increased incidence in the recent
past or a potential to increase in the near future.
Acute - develops rapidly, but last only a short time (flu)
Zoonoses – disease of animals which can be transmitted to humans
(Table 14.2, p. 419)
Chronic - develops more slowly, and often is less severe, but can be
continual or recurrent
Latent - inactive for a time (may be long or short)
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Extent of Host Involvement
Classification of Infection
How much of the body is affected?
Local infection - limited to a relatively small portion of the body.
Primary infection - an acute infection that causes the initial illness.
Systemic (generalized) infection - spread throughout the body
!bacteremia - bacteria present in blood
!septicemia - microorganisms multiply in the blood
!toxemia - presence of toxins in the blood (tetanus)
!viremia - is viruses in the blood
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Secondary infection - an opportunistic pathogen taking advantage of
the weakened defenses due to the primary infection.
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Spread of Infection - Reservoirs
Transmission of Disease
Reservoirs: source of infection, can be living or non-living.
Contact transmission - direct or indirect contact, or by droplet
transmission. No intermediate. Ex. kissing, touching.
Humans - transmit from person to person. Called carriers, some of
which may not exhibit symptoms.
Indirect contact - spread to susceptible host through a non-living
object, called a fomite.
Animals - (zoonoses) Can occur through contact with the animal, with
animal waste, ingestion of animal products, or by insect vectors.
Droplet transmission - mucus droplets spread a short distance (less
than one meter) by talking, sneezing, coughing, etc.
Non-living - soil and water. (ex. fungi in soil, botulism and tetanus;
water - cholera)
Vehicle transmission - transmission of disease agents by a medium
such as food, water or air (more than 1 meter)
Vector transmission - animals which carry pathogens from one host to
another. (arthropods commonly vectors)
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Nosocomial Infections
Nosocomial Infections - those infections not evident (present or
incubating) at the time of admission to a hospital. (5-15% of all
hospital patients acquire nosocomial infections)
Factors
microorganisms in the hospital
weakened state of the patient (primary infection, drug or radiation
therapy, burns or surgery)
chain of transmission in the hospital - can transfer patient to patient,
staff to patient
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used to be mainly Gram-positive, but now mostly Gram-negatives
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Control of Nosocomials
preventative procedures
Good aseptic technique
isolation
use of disposable or carefully sterilize equipment before reusing
monitoring procedures to trace causes.
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Development of a Disease
Incubation
Period
Incubation period - time between infection and appearance of
symptoms or signs.
Death if immune response
or medical intervention fail
Disease Decline
Illness
Prodromal period - in some diseases, short period of mild symptoms.
Prodromial
Period
Convalescence
Period of Illness - most acute. Exhibits overt signs and symptoms. If
not successfully overcome, the patient dies during this period. If
overcome, then enter the
Period of Decline - signs and symptoms diminish, susceptible to
secondary infections.
Period of Convalescence - regains strength and returns to prediseased
state
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Epidemiology
CDC
Epidemiology - study of when and where diseases occur and how they
are transmitted in populations.
Case reporting of certain disease cases to the state and national level.
Used to keep track of the spread of diseases.
Descriptive epidemiology - collection of data that describe the
occurrence of the disease under study.
Centers for Disease Control and Prevention (CDC) - central source of
epidemiological information in the U.S. Publishes Morbidity and
Mortality Weekly Report.
Analytical epidemiology - analyzes a particular disease to determine
its probable cause. (risk factors, etc.)
Morbidity - incidence of specific diseases
Experimental epidemiology - makes hypothesis about a particular
disease and experiments to test this hypothesis with a group of people.
Mortality - number of deaths from these diseases.
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